Differential Diagnosis and Daubert: Preventing the Misuse of Differential Etiology to Prove Causation in Toxic Tort Cases

By: Anthony G. Hopp, Jeremy S. Goldkind and David M. Cummings

Tony Hopp is a partner in the Chicago office of Steptoe & Johnson LLP. His practice focuses on commercial, environmental and toxic tort litigation.

Jeremy Goldkind is also a partner in Steptoe’s Chicago office. His practice concentrates on complex commercial disputes and product liability matters, including toxic tort.

David Cummings is an associate in Steptoe’s Chicago office.

n , a differential the process is intended to result in diagnosis is a technique a . I sometimes use to The term “differential identify the of a patient’s diagnosis” has often been used in symptoms. As its name indicates, toxic tort litigation to mean something completely different. A 2 DEFENSE COUNSEL JOURNAL | JANUARY 2017

plaintiff who files a toxic tort case such opinions. The goal of this should already have a medical article is to place defense counsel in diagnosis. Indeed, it should be the the best position to exclude diagnosis which leads the plaintiff differential etiology opinions and, if to file the lawsuit in the first place. the opinions survive the defense The toxic tort “differential challenge, to cross examine the diagnosis” is not a diagnosis at all, expert. but rather a method whereby a plaintiff’s expert purports to “rule I. in in” various potential causes for the Perspective: The plaintiff’s illness and then to “rule Daubert/Frye Framework out” alternative causes until only and the Plaintiff’s Burden one cause remains. It should come as no surprise to defense attorneys The cases in which courts have that, when a plaintiff’s expert uses admitted speculative differential the technique, it inevitably points to etiology opinions generally appear the defendant. to be ones in which the courts have The more accurate name for the ignored the Daubert or Frye technique as used in litigation is standard and accepted the expert’s “differential etiology.” Yet, courts characterization that his or her persist in calling it a differential causation opinion is based on diagnosis and sometimes confuse clinical experience or professional the medical standard for diagnosing judgment. To be in the best position an illness with the legal standard to keep such testimony out of for determining cause and effect. evidence, the defense lawyer must When that happens, a plaintiff’s plan the expert’s deposition in such expert may be allowed to introduce a way that the expert either agrees causation opinions that are based with the generally-accepted legal on unscientific speculation. standard for proving causation or The case law on differential admits that he or she did not follow diagnosis is inconsistent and that standard. A Daubert or Frye sometimes contradictory. This motion should follow. article is intended as a guide for defense lawyers who are facing A. Daubert: , not claims in which the plaintiff’s speculation expert purports to base his or her causation opinion on a differential The purpose of Federal Rule of etiology. It will explore the method Evidence 702 is to ensure that any as it has been employed in state and and all scientific testimony or federal courts, and provide some evidence admitted is not only practice tips for defending against Differential Diagnosis and Daubert 3

relevant, but reliable. 1 The One obstacle to mounting a Supreme Court has explained that Daubert challenge to a differential an expert must employ in the etiology opinion is that many courts courtroom the same level of have already accepted the intellectual rigor that characterizes technique as a valid method for the practice of an expert in the determining causation. 6 As set relevant field. 2 The “knowledge” forth below, there should still be requirement of Rule 702 requires room to attack a differential “more than subjective belief or etiology by arguing that the expert unsupported speculation.”3 applied the technique in an When deciding a Daubert unreliable and unscientific way. challenge, the judge’s task is to separate real science from B. Joiner and the “analytical speculation masquerading as gap” science. Daubert cautioned, however, that the trial court’s focus The Supreme Court’s decision “must be solely on principles and in General Electric v. Joiner dealt methodology, not on the conclusions with extrapolation from animal that they generate.”4 Since Daubert, studies to human results. 7 The appellate courts have sometimes plaintiff’s experts had relied on reversed trial courts because the “relevant animal studies which trial courts focused more on the support their opinions” and a expert’s conclusion (with which it handful of human epidemiology disagreed) rather than on the studies to conclude that PCBs expert’s methodology.5 caused plaintiff’s lung .8 The Supreme Court observed that the

1 Daubert v. Merrell Dow Pharm., Inc., 509 6 Clausen v. M/V New Carissa, 339 F.3d U.S. 579, 589 (1993). 1049, 1057 (9th Cir. 2003); Ervin v. Johnson 2 Kumho Tire Co. v. Carmichael, 526 U.S. & Johnson, Inc., 492 F.3d 901, 904 (7th Cir. 137, 152 (1999). 2007); McClain v. Metabolife Int’l, Inc., 401 3 Daubert, 509 U.S. at 590; see also Demaree F.3d 1233, 1252 (11th Cir. 2005); Goebel v. v. Toyota Motor Corp., 37 F. Supp.2d 959, Denver & Rio Grande W. R.R. Co., 346 F.3d 961 (W.D. Ky. 1999) (finding that an 987, 999 (10th Cir. 2003); Cooper v. Smith expert’s subjective belief or unsupported & Nephew, Inc., 259 F.3d 194, 202 (4th Cir. speculation is not admissible). 2001); Turner v. Iowa Fire Equip. Co., 229 4 Daubert, 509 U.S. at 594-595 (emphasis F.3d 1202, 1208 (8th Cir. 2000); Baker v. added); see also Chapman v. Proctor & Dalkon Shield Claimants Trust, 156 F.3d Gamble Distrib., LLC, 766 F.3d 1296, 1305 248, 253 (1st Cir. 1998); Ambrosini v. (11th Cir. 2014); McDowell v. Brown, 392 Labarraque, 101 F.3d 129, 140 (D.C. Cir. F.3d 1283, 1298 (11th Cir. 2004). 1996). 5 See Milward v. Acuity Prods. Grp., 7 Gen. Elec. Co. v. Joiner, 522 U.S. 136, 144 Inc., 639 F.3d 11, 26 (1st Cir. 2011); Schultz (1997). v. Akzo Nobel Paints, LLC, 721 F.3d 426, 434 8 Id. at 143. (7th Cir. 2013). 4 DEFENSE COUNSEL JOURNAL | JANUARY 2017

animal studies were on infant mice conclude that there is who had received direct injections simply too great an of high doses of PCBs, whereas the analytical gap between the plaintiff was an adult male who had data and the opinion been exposed to much lower proffered.9 concentrations. The mice also developed a different form of Joiner both clarified and cancer. complicated the district court’s Plaintiff defended his experts’ gatekeeper role. It freed district opinions by claiming that, under courts from focusing exclusively on Daubert, the court’s focus should be an expert’s methodology in on “principles and methodology” determining whether opinions are and not on the experts’ conclusions. admissible, but also saddled the The Supreme Court responded with court with the sometimes murky perhaps the most widely quoted responsibility of determining language in all of Daubert whether the “analytical gap” jurisprudence: between an expert’s source material and his or her conclusions is “too wide.” After Joiner, district But conclusions and courts were free to review methodology are not epidemiological studies, animal entirely distinct from one studies, in vitro studies and other another. Trained experts forms of scientific proof in order to commonly extrapolate evaluate whether the relevant from existing data. But scientific studies supported the nothing in either Daubert experts’ conclusions. 10 or the Federal Rules of Joiner provided no guidance for Evidence requires a the lower courts on how to tell district court to admit when “the gap” was “too great.” opinion evidence that is Ever since, district courts have connected to existing data generally observed that the only by the ipse dixit of the Daubert/Joiner analysis is fact expert. A court may specific and case-by-case.11 While

9 Id. at 146 (emphasis added). 10 FEDERAL JUDICIAL CENTER, REFERENCE MANUAL ON SCIENTIFIC EVIDENCE 23 (3d ed. 2011). 11 Loewen v. Wyeth, Inc., No. CV 03-J-2166- S, 2011 WL 6140908, at *1 (N.D. Ala. Nov.

14, 2011) (“the inquiry required by Daubert is meant to be a ‘flexible one,’ and expert testimony which does not meet all or most Differential Diagnosis and Daubert 5

some courts merely seek to between the evidence on which the evaluate the “weight” of the expert purports to rely and the scientific evidence without closely ultimate result is too wide. examining that evidence, other courts have rolled up their sleeves C. The Frye standard: and dug into the often-unfamiliar General acceptance territories of toxicology, epidemiology and animal research In jurisdictions that follow the at a granular level.12 The Seventh Frye standard, the court’s focus is Circuit recently described the on whether the expert’s theory is analysis this way: “The district generally accepted in the relevant court’s primary concern, and ours scientific community. 14 Even in on appeal, is the failure of the Frye jurisdictions, many courts experts to connect the dots from the have added a reliability test. That studies to the illnesses endured by is, the technique the expert applies the [plaintiffs].” 13 The Joiner/ must give rise to reliable results analytical gap assault is another and the expert must have applied potential strategy for keeping a the technique in a reliable manner. speculative differential etiology The addition of the “reliability” opinion out of evidence. The element in Frye jurisdictions gives defense lawyer can argue that the courts wider latitude to exclude dots do not connect because the gap expert opinions, and some courts

of the Daubert factors may still be reasonably support the conclusions of the admissible based on the specific facts of a Plaintiffs’ expert witnesses”); Hamilton v. particular case”); Nelson v. Wal-Mart Stores, Breg, Inc., No. 2:09-CV-146, 2011 WL Inc., No. 2:04-CV-00171-WRW, 2009 WL 833614, at *3-8 (S.D. Ohio Jan. 24, 2011) 330299, at *1 (E.D. Ark. Jan. 13, 2009) (conducting a review of multiple expert (“Because the [Daubert] inquiry is ‘flexible studies); Mercer v. Rockwell Int’l Corp., 24 and fact-specific, a court should use, adapt, F. Supp.2d 735, 747-748 (W.D. Ky. 1998) or reject Daubert factors’ as needed based (discussing various epidemiological studies on the facts of a particular case.”) (citation relied upon by expert witness); Baker v. omitted); Target Corp. v. Greenberg Farrow Chevron USA, Inc., 680 F. Supp.2d 865, 880- Architecture, Inc., No. CIV. 10-4810 887 (S.D. Ohio 2010) (conducting an RHK/JSM, 2012 WL 1963362, at *10 (D. extensive review of various epidemiology Minn. May 31, 2012) (“Even a theory that studies), aff’d sub nom. Baker v. Chevron meets certain Daubert factors should not be U.S.A. Inc., 533 Fed. App’x 509 (6th Cir. admitted if it does not apply to the specific 2013). facts of the case.”). 13 C.W. ex rel. Wood v. Textron, Inc., 807 12 See In re Breast Implant Litig., 11 F. F.3d 827, 837 (7th Cir. 2015) (emphasis Supp.2d 1217, 1231 (D. Colo. 1998) (stating added). that the court “examined the numerous 14 See, e.g., Zandi v. Wyeth, No. A08-1455, studies” submitted by the plaintiffs, 2009 WL 2151141, at *5 (Minn. Ct. App. July including 40 epidemiology studies, and 21, 2009). determined that the studies “do not 6 DEFENSE COUNSEL JOURNAL | JANUARY 2017

have applied the “Frye plus differential diagnosis is a technique reliability” standard to exclude used to identify, i.e., diagnose, the differential etiology opinions.15 plaintiff’s illness, not to determine the cause of the plaintiff’s illness.17 II. Differential Diagnosis vs. For example, in Tamraz v. Differential Etiology Lincoln Electric Company, 18 the court criticized the plaintiff’s expert The terms differential diagnosis for conflating diagnosis and and differential etiology sound etiology. The plaintiff had been similar, but they describe vastly exposed to manganese, but different processes. The Federal developed Parkinson’s, not Judicial Center’s Manual on manganism. Manganism is caused Scientific Evidence defines the term by exposure to manganese, “differential diagnosis” as: Parkinson’s is not. The two conditions share similar symptoms, The method by which a but arise from damage in different determines parts of the brain. The plaintiff’s what process has expert called the plaintiff’s illness caused a patient’s “manganese-induced symptoms. The physician parkinsonism,” and attempted to considers all relevant “elide[ ] the distinction between potential causes of the [plaintiff’s] disease and what symptoms and then caused it.” 19 The Sixth Circuit eliminates alternative excluded the opinion, but still held causes based on a that a differential etiology – when , done correctly – is an admissible clinical tests and a method for proving causation. thorough case history.16 The court noted that, when most physicians think about Somewhat paradoxically, even etiology in a clinical setting, they courts that have allowed plaintiff’s may think about it in a different way experts to testify to a differential than judges and juries think about it etiology have recognized that a in a courtroom. Getting a diagnosis

15 Berry v. CSX Transp., Inc., 709 So.2d 552, 17 Brown v. Burlington N. Santa Fe Ry. Co., 568 (Fla. Dist. Ct. App. 1998); Montgomery 765 F.3d 765, 772 (7th Cir. 2014); Higgins v. Mut. Ins. Co. v. Chesson, 206 Md.App. 569, Koch Dev. Corp., 794 F.3d 697 (7th Cir. 2015) 594 (Md. App. 2012); Cornell v. 360 W. 51st (“‘Differential diagnosis’ actually refers to a St. Realty, LLC, 22 N.Y.3d 762, 780-781 (N.Y. method of diagnosing an ailment, not 2014); Blackwell v. Wyeth, 408 Md. 575, determining its cause.”). 584 (Md. 2009). 18 620 F.3d 665 (6th Cir. 2010). 16 FEDERAL JUDICIAL CENTER, REFERENCE 19 Id. at 673. MANUAL ON SCIENTIFIC EVIDENCE 214 (1994). Differential Diagnosis and Daubert 7

right matters greatly to a treating method of diagnosing an ailment, physician, as a bungled diagnosis not determining its cause. can lead to an unnecessary ‘Differential etiology,’ on the other procedure, or worse. But with hand, is a causation-determining etiology, the physician may follow a methodology. But, to be validly precautionary approach. If a conducted, an expert must particular factor might cause the systematically ‘rule in’ and ‘rule out’ disease, the physician may tell the potential causes in arriving at her patient to avoid it. In other words, ultimate conclusion.”22 according to the Sixth Circuit, Unfortunately, few courts physicians apply a less stringent acknowledge the distinction standard to evaluating etiology between diagnosis and etiology. A than they do to diagnosing an Daubert or Frye motion attacking a illness. The Sixth Circuit went on to differential diagnosis, therefore, observe that in its own prior should begin by establishing the opinions, 20 it had used the term appropriate method for reliably “differential diagnosis” to broadly proving causation and should include what might better be called demonstrate how the plaintiff’s a differential etiology. But the court expert’s opinion does not satisfy had never before been forced to that standard. Fortunately, both distinguish the two concepts. The inside and outside the context of Tamraz court appeared to differential diagnosis, courts have recognize that using the terms addressed the “right” way to prove “diagnosis” and “etiology” causation, and there is a robust interchangeably had resulted in body of case law on the subject. admitting opinions into evidence which were not reliably grounded A. General Causation: The in science. substance can cause the The court concluded, “This low disease threshold for making a decision serves well in the but not in It is by now arguably hornbook the courtroom, where decision law in both Daubert and Frye requires not just an educated hunch jurisdictions that proving medical but at least a preponderance of the causation in a toxic tort case is a evidence.”21 Similarly, the Seventh two-step analysis. It requires proof Circuit has recently highlighted the of both “general causation” and distinction, observing, “‘Differential diagnosis’ actually refers to a

20 Hardyman v. Norfolk & W. Ry. Co., 243 22 Higgins, 794 F.3d at 705 (internal F.3d 255, 260 n.2 (6th Cir. 2001). citations omitted) (emphasis in original). 21 Tamraz, 620 F.3d at 673. 8 DEFENSE COUNSEL JOURNAL | JANUARY 2017

“specific causation.” 23 General ignored.26 This is particularly true causation is a question of whether if there are negative the chemical at issue can cause the epidemiological studies which are injury alleged by the plaintiff.24 It is directly on point (i.e., studies that proven by demonstrating, have looked for the alleged primarily through the medical and association and not found it). scientific literature, that exposure Where there is a large body of to a substance is capable of causing epidemiological evidence that a particular disease. contradicts a plaintiff’s claim, it is Proof of general causation necessary for the plaintiff to at least almost always requires the use of address it with evidence that is epidemiology. 25 Where based on medically reliable and epidemiology is available, courts scientific methodology.27 have held that it cannot be

23 Pluck v. BP Oil Pipeline Co., 640 F.3d 671, (affirming grant of summary judgment for 676-677 (6th Cir. 2011); McClain, 401 F.3d defendants because the evidence relied at 1239; Dickson v. Nat’l Maint. & Repair of upon by plaintiffs, which did not include Ky., Inc., No. 5:08-CV-00008, 2011 WL epidemiological studies, was an insufficient 12538613, at *2 (W.D. Ky. April 28, 2011); basis for an opinion on causation), cert. Siharath v. Sandoz Pharms. Corp., 131 F. denied, 506 U.S. 826 (1992); see generally In Supp.2d 1347, 1363 (N.D. Ga. 2001); Adams re Breast Implant Litig., 11 F. Supp.2d at v. Cooper Indus., Inc., No. CIV.A. 03-476-JBC, 1224 (collecting cases standing for the 2012 WL 2339741, at *1 (E.D. Ky. June 19, proposition that epidemiological studies 2012); Ex parte Valdez, 636 So.2d 401, 405 are the best evidence of causation). “Courts (Ala. 1994); Berry, 709 So.2d at 567-568; should normally require more than one Chesson, 206 Md.App. at 606-607; Sean R. ex epidemiological study showing a positive rel. Debra R. v. BMW of N. Am., LLC, 48 association to establish general causation, N.E.3d 937 (N.Y. 2016); Blum by Blum v. because a study’s results must be capable of Merrell Dow Pharm., Inc., 705 A.2d 1314, replication.” Dickson, 2011 WL 12538613, 1316 (Pa. Super. Ct. 1997), aff’d sub nom. at *6 (citing King v. Burlington N. Santa Fe Blum ex rel. Blum v. Merrell Dow Pharm., Ry. Co., 762 N.W.2d 24, 48 (Neb. 2009)). Inc., 764 A.2d 1 (Pa. 2000). 26 Norris, 397 F.3d at 882. 24 See McClain, 401 F.3d at 1239. 27 Id.; Turpin v. Merrell Dow Pharm., Inc., 25 See, e.g., Dickson, 2011 WL 12538613 at 736 F. Supp. 736, 743 (E.D. Ky. 1990) *5 (“Epidemiology is usually the best (determining that, where there were over evidence of general causation in toxic tort 30 epidemiological studies, none of which cases”); Norris v. Baxter Healthcare Corp., found a statistically significant relationship 397 F.3d 878, 882 (10th Cir. 2005) (citing between defendant’s product and plaintiffs’ Linda A. Bailey, et al., Reference Guide on disease, plaintiffs could not meet their Epidemiology, REFERENCE MANUAL ON burden); Conde v. Velsicol Chem. Corp., 24 SCIENTIFIC EVIDENCE 126 (1994)); Castellow v. F.3d 809, 814-815 (6th Cir. 1994) (finding Chevron USA, 97 F. Supp.2d 780, 786 (S.D. that plaintiffs failed to account for nineteen Tex. 2000) (citing Allen v. Pa. Eng’g Corp., contrary studies, and therefore granting 102 F.3d 194, 196 (5th Cir. 1996)); see also summary judgment in favor of defendants Turpin v. Merrell Dow Pharm., Inc., 959 F.2d was warranted); see also Grant v. 1349, 1351-1356, 1360 (6th Cir. 1992) Pharmavite, LLC, 452 F. Supp.2d 903, 908 Differential Diagnosis and Daubert 9

Of course, simply identifying analysis often comes into play. one (or even a handful) of positive There are only a handful of studies does not end the inquiry. situations in which courts will The plaintiff’s expert must examine assume, without expert evidence, both the positive and negative that a substance is capable of results using the Bradford Hill causing a particular disease. 29 criteria or some other objective These include asbestos and standard in order to prove that the ; silica and silicosis; association is truly causal, and not cigarettes and ; and just an anomaly. 28 The plaintiff alcohol and .30 For the vast must establish general causation by majority of cases, the court will not reference to published literature assume that general causation has and must use some type of been established, and a plaintiff’s transparent, reproducible method experts will be required to prove for analyzing the available science if that the studies on which they rely the expert is to prove that his or her demonstrate a causal relationship analysis is “reliable.” between the defendant’s product The general causation stage is and the plaintiff’s disease at some where the Joiner “connect the dots” dose level. The court will be asked

(D. Neb. 2006) (“This is not a case where 1071, 1081 (D. Minn. 2008); In re Stand ‘N there is no epidemiology. Instead, it is a Seal Prods. Liab. Litig., 623 F. Supp.2d 1355, case where the body of epidemiology finds 1373 (N.D. Ga. 2009); Rimbert v. Eli Lilly & no association”); In re Bausch & Lomb, Inc. Co., No. CIV 06-0874 JCH/LFG, 2009 WL Contact Lens Solution Prods. Liab. Litig., No. 2208570, at *14 (D. N.M. July 21, 2009) CIV A 2:06MN77777DCN, 2009 WL (stating that expert testified that the Hill 2750462, at *14 (D. S.C. Aug. 26, 2009) criteria are generally accepted); In re (finding that the failure to address contrary Trasylol Prods. Liab. Litig., No. 08-MD- data renders plaintiff’s theory inherently 01928, 2010 WL 1489734, at *10 (S.D. Fla. unreliable). Mar. 8, 2010) (finding that experts’ method, 28 See In re Joint E. & S. Dist. Asbestos Litig., including the Hill criteria, was “scientifically 52 F.3d 1124, 1128-1130 (2d Cir. 1995); reliable”); Kristensen ex rel. Kristensen v. Gannon v. United States, 571 F. Supp.2d 615, Spotnitz, No. 3:09-cv-00084, 2011 WL 626-627 (E.D. Pa. 2007) (stating 4566239, at *9 (W.D. Va. Sept. 30, 2011) preeminent scientists have relied on the Hill (stating that the Hill criteria are “widely criteria to determine causation); Castellow, accepted in toxic exposure causation 97 F. Supp.2d at 786-787 (stating that analyses”); In re Zoloft (Sertraline expert testified “without contradiction[] Hydrocloride) Prods. Liab. Litig., 26 F. that scientists generally rely on the Supp.3d 466, 474-475 (E.D. Pa. 2014); In re Bradford-Hill factors to ascertain valid Actos (Pioglitazone) Prods. Liab. Litig., No. opinions on medical causation”); 12-cv-00064, 2014 WL 60324, at *6 (W.D. Amorgianos v. Nat. R.R. Passenger Corp., La. Jan. 7, 2014) (stating that the Hill criteria 137 F. Supp.2d 147, 167-168 (E.D.N.Y. are “both reliable and credible”). 2001); Rains v. PPG Indus., Inc., 361 F. 29 See McClain, 401 F.3d at 1239. Supp.2d 829, 835-836 (S.D. Ill. 2004); In re 30 Id.; see also Hendrix ex. rel. G.P. v. Evenflo Viagra Prods. Liab. Litig., 572 F. Supp.2d Co., 609 F.3d 1183, 1196 (11th Cir. 2010). 10 DEFENSE COUNSEL JOURNAL | JANUARY 2017

to determine whether “the gap” plaintiff’s disease. 31 To establish between the studies’ conclusions specific causation, a plaintiff must and the plaintiff’s illness is “too show: (i) proof of exposure to the wide.” When “ruling in” the substance; (ii) that the exposure or defendant’s product as a potential dose levels were comparable to or cause of the plaintiff’s illness, greater than those in therefore, the plaintiff’s expert epidemiological studies; (iii) that should be required to provide a the exposure occurred before the robust, transparent and onset of injury; and (iv) that the reproducible general causation timing of the onset of injury was analysis. consistent with that experienced by those in the study.32 This is often B. Specific Causation: The referred to as a “dose-response substance did cause the relationship.” disease Toxicologists recognize that substances have threshold doses. Proof of specific causation Courts generally reject the notion means that a plaintiff’s actual that there is “no safe dose” of toxic exposure to the alleged toxin was at substance, even a carcinogen.33 As a level sufficient to cause the

31 See, e.g., Pluck, 640 F.3d at 677; Raynor v. 32 Pluck, 640 F.3d at 677. Merrell Pharm., Inc., 104 F.3d 1371, 1376 33 Id. at 675 (finding an expert witness’s (D.C. Cir. 1997); Dickson, 2011 WL testimony unreliable because “he relied 12538613, at *2; Adams v. Cooper Indus., upon a ‘no safe dose’ theory that had been Inc., No. CIVA 03-476 JBC, 2007 WL discredited by other courts as a basis for 2219212, at *2 (E.D. Ky. July 30, 2007); establishing specific causation”); Moore v. Savage v. Union Pac. R.R. Co., 67 F. Supp.2d Ashland Chem. Inc., 151 F.3d 269, 278 (5th 1021, 1031 (E.D. Ark. 1999); Cano v. Cir. 1998) (excluding expert witness Everest Minerals Corp., 362 F. Supp.2d 814, testimony in part because the expert 824 (W.D. Tex. 2005); Sean R. ex rel. Debra offered no scientific support for his general R., 48 N.E.3d 937; Ex parte Valdez, 636 So.2d theory that “exposure to Toluene solution 401 (Frye jurisdiction requiring proof of at any level would cause RADS”); Cano, 362 specific causation). F. Supp.2d at 849 (“Several courts have considered and rejected the use of the linear no-threshold model in the litigation context.”); In re Denture Cream Prods. Liab. Litig., 795 F. Supp.2d 1345, 1352 (S.D. Fla. 2011) (“for most types of dose-response relationships following chronic (repeated) exposure, thresholds exist, such that there is some dose below which even repeated, long-term exposure would not cause an effect in any individual”); Henricksen v. ConocoPhillips Co., 605 F. Supp.2d 1142, 1166 (E.D. Wash. 2009) (“Sawyer’s theory Differential Diagnosis and Daubert 11

a result, even in cases in which the not require plaintiffs to prove plaintiff’s experts apply a exposure or dose with differential diagnosis approach, mathematical precision, some some courts have still held that the degree of relative quantification is experts must provide admissible required (i.e., how much exposure evidence of the dose or exposure is enough to cause the illness?).35 level required to cause the A plaintiff’s expert using a plaintiff’s illness.34 While courts do differential etiology approach

that any amount of exposure more than of exposure to above-ambient levels of the negligible should be considered substantial alleged toxin, and instead requires evidence risk factor for AML flies in the face of the of the levels of exposure that are hazardous scientific literature reviewed and other to human beings generally, as well as the expert testimony in this case that there is a plaintiff’s actual level of exposure to the threshold or dose below which you do not defendant's toxic substance”); Gregg v. V-J see a statistically significant risk of Auto Parts, Co., 943 A.2d 216, 226-227 (Pa. developing AML.”); Adams, 2007 WL 2007) (“we do not believe that it is a viable 2219212, at *7 (“The court finds that the solution to indulge in a fiction that each and ‘no-safe-dose’ theory is not a reliable every exposure to asbestos, no matter how methodology, and it rejects the plaintiffs' minimal in relation to other exposures, claim that said theory entitled their specific implicates a fact issue concerning causation experts to pay so little attention substantial-factor causation”). to the level of exposure in the bellwether 34 Pluck, 640 F.3d at 677-680; Dickson, 2011 plaintiffs.”); Wills v. Amerada Hess Corp., WL 1258613, at *7-10. No. 98 CIV. 7126 (RPP), 2002 WL 140542, 35 See Nelson v. Tenn. Gas Pipeline Co., No. at *14 (S.D.N.Y. Jan. 31, 2002) (“‘To the 95-1112, 1998 WL 1297690, at *6 (W.D. extent that it has been subjected to peer Tenn. Aug. 31, 1998) (stating that an review and publication, [the no threshold appropriate methodology requires model for carcinogenic effects] has been evidence from which the trier of fact could rejected by the overwhelming majority of conclude that the plaintiff was exposed to the scientific community.’”) (quoting levels of toxins sufficient to cause the harm Whiting v. Boston Edison Co., 891 F. Supp. complained of); McClain, 401 F.3d at 1242- 12, 25 (D. Mass. 1995)); Sutera v. Perrier 1243 (11th Cir. 2005) (stating that expert’s Grp. of Am. Inc., 986 F. Supp. 655, 666 (D. opinion that “any amount of Metabolife” Mass. 1997); Johnston v. United States, 597 was too much “clearly contradict[ed] the F. Supp. 374, 393 (D. Kan. 1984) (noting principles of reliable methodology” as he that the linear no-threshold hypothesis is offered “no opinion about the dose of an assumption and that regulators use this Metabolife” that purportedly caused the model because it is more prudent to plaintiffs’ ailments); Henricksen, 605 F. overestimate risk than to underestimate it Supp.2d at 1161-1162 (stating that expert and “just because scientists use hypotheses opinion failed to quantify plaintiff’s level of to describe something they really don’t exposure to benzene and although “proof know for sure does not justify a court of law of . . . exposure through specific quantitative in using speculative hypotheses to measurement is not a requirement, determine that one person has caused harm exposure at some level must be shown to another”); Richardson v. Union Pac. R. Co., before a link between benzene exposure 386 S.W.3d 77, 79 (Ark. Ct. App. 2011) and AML could be drawn”). (“causation requires more than mere proof 12 DEFENSE COUNSEL JOURNAL | JANUARY 2017

should be required to satisfy II. Differential Diagnosis in the specific causation as a part of Courtroom “ruling in” the defendant’s product. Unless the plaintiff’s expert can A. Differential Diagnosis establish that the plaintiff’s misapplied exposure was high enough to cause his or her illness, there should be no As indicated above, a clinical basis for ruling in the defendant’s differential diagnosis shares certain product as a cause. surface similarities with a A significant handful of courts differential etiology causation have held that a differential opinion. Both techniques purport diagnosis can only be used to to “rule in” certain causes and to establish specific causation and that “rule out” others. The critical the method should not even be distinction is that, in the clinical considered if the plaintiff has not setting, “cause” means diagnosis, already proven general causation.36 while in the legal setting “cause” Other courts have either disagreed means a proximate cause. As the or ignored the distinction Sixth Circuit recognized in Tamraz, completely.37 Still others have held the standard for assigning a cause that a differential diagnosis is a in the clinical setting is less substitute for a dose/response. 38 stringent than the standard the The most sensible rule appears to courts use to find proximate cause. be that the established standards But when the same word and the for proving specific causation apply same rule in/rule out technique whether or not the expert is using a apply to two such disparate differential diagnosis. The defense concepts, it is no wonder that courts lawyer should attempt to persuade have mistakenly allowed experts to the court to apply the established apply the less stringent, clinical standard. approach without pausing to recognize the difference between “causation” and “etiology.” Courts from around the country have held

36 Kilpatrick v. Breg, Inc., 613 F.3d 1329, Supp. 1387, 1413 (D. Or. 1996); Ruggerio v. 1343 (10th Cir. 2010) (stating a differential Warner Lambert Co., 424 F.3d 249, 254 (2d diagnosis “assumes the existence of general Cir. 2005); Blackwell, 408 Md. at 615. causation”); In re Meridia Prods. Liab. Litig., 37 See, e.g., C.W. ex. rel. Wood, 807 F.3d at 328 F. Supp.2d 791, 799 (N.D. Ohio 2004), 839; Ruggerio, 424 F.3d at 254. aff’d, 447 F.3d 861 (6th Cir. 2006); Harvard 38 Westberry v. Gislaved Gummi AB, 178 v. Baxter Int’l. Inc., 2000 U.S. Dist. LEXIS F.3d 257 (4th Cir. 1999); Hardyman, 243 21316, at *17 (N.D. Ohio July 21, 2000); F.3d at 260-261; Cutlip v. Norfolk S. Co., No. Cornell, 9 N.E.3d at 900; Norris, 397 F.3d at L-02-1051, 2003 WL 1861015 (Ohio App. 885; Hall v. Baxter Healthcare Corp., 947 F. April 11, 2003). Differential Diagnosis and Daubert 13

that a “differential diagnosis” is a In Best v. Lowe’s Home Centers, standard scientific technique for Inc., 42 the Sixth Circuit defined a identifying the cause of a medical three-part test for when a condition.39 The Third Circuit has differential etiology opinion is noted that “differential diagnosis reliable and admissible. The generally is a technique that has expert: widespread acceptance in the medical community, has been (1) objectively ascertains, subject to peer review, and does not to the extent possible, the frequently lead to incorrect nature of the plaintiff’s results.”40 The Seventh Circuit has injury . . . , stated that there is “nothing (2) “rules in” one or more controversial” about using causes of the injury using a differential diagnosis to establish valid methodology, and legal cause. A large number of (3) engages in standard reported decisions reflect the diagnostic techniques by confusion between diagnosis and which doctors normally legal cause.41 rule out alternative causes to reach a conclusion as to which cause is most likely.43

Best applied a clinical standard when it should have applied a legal one. The plaintiff splashed pool chemicals into his face in 2003, but the expert did not diagnose his condition (anosmia – loss of the sense of smell) and conduct his differential diagnosis until 2008. The court admitted that there was

39 Hardyman, 243 F.3d at 260; Westberry, expert’s] assessment of causation was 178 F.3d at 263; Turner, 229 F.3d at 1208; unreliable”); Perkins v. Origin Medsystems, Baker, 156 F.3d at 253 (“Indeed, Inc., 299 F. Supp.2d 45, 57 (D. Conn. 2004) ‘differential diagnosis’ is a standard medical (“differential diagnosis, is a standard technique.”); In re Paoli R.R. Yard PCB Litig., scientific technique of identifying the cause 35 F.3d 717, 733 (3d Cir. 1994) (“in the of a medical problem”); Castillo v. E.I. absence of employment of standard DuPont De Nemours & Co., Inc., 854 So.2d techniques of differential diagnosis, and 1264, 1271 (Fla. 2003). failure to provide any explanation as to why 40 In re Paoli, 35 F.3d at 758. he concluded that PCBs rather than 41 See, e.g., Schultz, 721 F.3d at 433. alternative possibilities had caused 42 563 F.3d 171, 179-180 (6th Cir. 2009). plaintiffs’ illnesses, we conclude that [the 43 Id. at 179. 14 DEFENSE COUNSEL JOURNAL | JANUARY 2017

no published literature associating could cause throat irritation. inhalation of the product with Despite defendant’s insistence that anosmia. The expert, however, not a single piece of medical “ruled in” the product as a potential literature said that glue fumes could cause based “on his own cause throat polyps, the court experience” and generic statements admitted the testimony citing in on the product’s MSDS, and the support the physician’s “review of Sixth Circuit approved. He also the MSDS” and “his training and ruled out a potential idiopathic experience.” cause for the injury based on “his Berry v. CSX Transportation, own experience.” The Sixth Circuit Inc. 45 was a FELA case in which a approved the expert’s approach to railroad worker alleged that causation because it was not exposure to solvents had caused “arbitrary” but was based on his him to develop toxic experience and general knowledge. encephalopathy. While the parties It is not difficult to find similar disagreed on the issue of general cases. In McCullock v. H.B. Fuller,44 causation, the court held that there the plaintiff developed throat was sufficient evidence that solvent polyps after being exposed to hot exposure could cause toxic glue fumes. Her treating physician, encephalopathy, so general “an experienced medical doctor” causation had been established. and board-certified otolaryn- In order to prove specific gologist, opined that the glue causation, the plaintiff turned to R. caused the polyps because the Michael Kelly, M.D.46 Dr. Kelly did MSDS for the product stated that it not provide any opinions on how

44 61 F.3d 1038 (2d Cir. 1995). 45 709 So.2d 552. 46 In 2008, Dr. Kelly was the focus of an exposé in the Wall Street Journal entitled Michigan Malpractice. Review & Outlook, Michigan Malpractice, WALL ST. J., Nov. 10, 2008, available at http://www.wsj.com/ articles/SB122628156208212443. The subject of the piece was Dr. Kelly’s work on an asbestos case in Michigan, Miles v. Sure Seal Prods. Co. Inc., No. 04-434812-NP, 2008 WL 5071712 (Mich. Cir. Ct. Nov. 19, 2008). In Miles, the trial court excluded Dr. Kelly’s opinions after finding that he had expressed nearly identical conclusions with respect to each of the 75 plaintiffs. The plaintiffs’ treating physicians and a panel of radiologists overwhelmingly concluded that the plaintiffs did not have the symptoms identified by Dr. Kelly or the Differential Diagnosis and Daubert 15

much exposure is necessary to be proved even when we don’t cause toxic encephalopathy or how know precisely how the damage much exposure plaintiff had. occurred, if there is sufficiently Instead, he took a compelling proof that the agent from the plaintiff and his wife, must have caused the damage obtained a work history from somehow.’” 47 This philosophy is plaintiff and ordered laboratory completely at odds with the well- tests, including an MRI and an EEG. developed legal standard for Dr. Kelly’s examination and tests proving general and specific appeared to be geared toward causation. confirming plaintiff’s medical diagnosis, rather than evaluating B. Differential Etiology the cause of his disease. The court correctly applied noted that Dr. Kelly provided a “biologically plausible explanation” A second line of cases takes a that the solvents have the ability to more stringent look at the elements dissolve fatty materials, making it of a differential diagnosis and more difficult for the body to analyzes the experts’ opinions metabolize them and thereby against the backdrop of Daubert, prolonging the exposure. The Frye, Joiner and related cases. prolonged exposure, in Dr. Kelly’s The Tamraz decision came out view, caused the plaintiffs toxic of the Sixth Circuit one year after encephalopathy. The trial court Best, but represents a completely held that Dr. Kelly’s opinions were different philosophy with respect to inadmissible under Frye, but the differential etiology. Best ignored appellate court reversed, noting Daubert and held that an expert that the differential diagnosis would be allowed to rule in and rule method is “scientifically out causes as long as he followed a acceptable.” “valid” methodology. The Best Even more distressing for court did not define “valid,” and the defense attorneys is the Ninth expert’s method was deemed Circuit’s recent rationale for acceptable because he said it was allowing a differential etiology into based on his experience. Had Best evidence: “Given the difficulties in applied a standard Daubert establishing a medical cause and approach, an expert opinion based effect relationship, ‘[c]ausation can

asbestos disease diagnosed by Dr. Kelly. Id. 47 Messick v. Novartis Pharm. Corp., 747 For further background on the Dr. Kelly F.3d 1193, 1198 (9th Cir. 2014) (internal controversy, see Mark A. Behrens, Asbestos citation omitted) (emphasis in original). Litigation Screening Challenges: An Update, 26 T.M. COOLEY L. REV. 721, 735-747 (2008). 16 DEFENSE COUNSEL JOURNAL | JANUARY 2017

on “experience” likely would not plaintiff’s Non-Hodgkin’s Lym- have been admitted. phoma because he did not ascertain Tamraz, by contrast, observed her level of benzene exposure or that calling something a differential determine whether the exposure diagnosis does not answer the was in excess of EPA mandated Daubert reliability question, but “safe” levels. The expert also did instead raises three more:48 not reliably “rule out” alternative causes. The expert acknowledged (1) Did the expert make an other exposures which could have accurate diagnosis of caused or contributed to the the nature of the plaintiff’s illness (i.e., cigarettes) disease? but did not identify his method for (2) Did the expert reliably discounting them. rule in the possible In Chapman v. Proctor & Gamble causes? Distribution, LLC, 51 the plaintiff (3) Did the expert reliably attempted to blame her denture rule out the rejected adhesive for her myelopathy. The causes?49 court held that a differential diagnosis cannot overcome the The seemingly subtle “fundamental failure of laying a distinction between Best and scientific groundwork for the Tamraz – substituting the word general toxicity of the and that “reliable” in the standard for the it can cause the harm a plaintiff word “valid” – had a profound suffered.”52 The expert in Chapman effect. The “reliability” standard had identified several potential comes from Daubert and the “Frye alternative causes for plaintiff’s plus reliability” case law and brings illness but failed to address them in to bear all of the law on how experts his opinion. The court held that an are required to prove general and expert must provide “reasons for specific causation. Other decisions rejecting alternative hypotheses follow a similar approach. using scientific methods and For example, in Pluck v. B.P. Oil procedures and the elimination of Pipeline Co., 50 the court held that those hypotheses must be founded the expert had failed to reliably rule on more than subjective beliefs or in benzene as a cause of the unsupported speculation.”53

48 Tamraz, 620 F.3d at 674 (citing Bowers v. Norfolk S. Corp., 537 F. Supp.2d 1343 (M.D. Ga. 2007)). 51 766 F.3d 1296. 49 Id. at 665. 52 Id. at 1309. 50 640 F.3d at 679-680. 53 Id. at 1310.

Differential Diagnosis and Daubert 17

Other courts evaluating steer the court toward an differential etiology opinions have interpretation of differential reached similar results. They have diagnosis that requires the full demanded transparent, reliable Daubert or “Frye plus reliability” methods for ruling in a substance as treatment. a potential cause of the plaintiff’s disease and by so doing have III. Practice Tips brought to bear the case law which states that epidemiology is the best The presence of the phrase evidence of general causation. 54 “differential diagnosis” in an They have also closely examined expert’s report, by itself, may be an the studies on which the experts indication that the expert is not relied in assessing general prepared to answer the traditional causation to see if the analytical gap questions about epidemiology and between the science and the dose response. For that reason, the opinion is too wide. 55 They have defense lawyer should take the time likewise looked at experts’ to build a careful record of both the approaches to specific causation to work that the expert did to compile determine whether the expert has the differential diagnosis, but more reliably extrapolated from the importantly, the work the expert dose/response literature to the did not do. At the end of the plaintiff’s individual exposure deposition, the defense attorney situation, and they have alluded to should have a transcript that proves the near impossibility of ruling out that the expert understood the alternative causes.56 The objective traditional method for proving of a defense attorney should be to causation, but intentionally chose not to follow it. Just as importantly,

54 Norris, 397 F.3d at 882 (“epidemiology is (“Epidemiology provides the best evidence the best evidence of general causation in a of general causation in toxic tort cases.”); toxic tort case”); Rider v. Sandoz Pharm. Zandi, 2009 WL 2151141 at *6 (stating that Corp., 295 F.3d 1194, 1198 (11th Cir. 2002) does not lend itself to (“Epidemiology, a field that concerns itself differential diagnosis because the scientific with finding the causal nexus between community has not accepted that breast external factors and disease, is generally cancer has a limited number of discrete considered to be the best evidence of causes, such that ruling out one cause causation in toxic tort actions.”); In re would implicate another). Breast Implant Litig., 11 F. Supp.2d at 1224 55 C.W. v. Textron, Inc., No. 3:10 CV 87 PPS, (“Epidemiology is the best evidence of 2014 WL 1047940, at *11, 14 (N.D. Ind. Mar. causation in the mass torts context.”); Baker, 17, 2014), aff’d sub nom., C.W. ex rel. Wood 680 F. Supp.2d at 875 (“Epidemiology is v. Textron, Inc., 807 F.3d 827 (7th Cir. 2015); usually the best evidence of general Moore, 151 F.3d at 279. causation in toxic tort cases.”); Burst v. Shell 56 Henricksen, 605 F.Supp.2d at 1157; Oil Co., No. CIV.A. 14-109, 2015 WL McClain, 401 F.3d 1233. 3755953, at *4 (E.D. La. June 16, 2015) 18 DEFENSE COUNSEL JOURNAL | JANUARY 2017

the defense lawyer should explore B. Break apart the “Ruling- in detail the expert’s rationale for In” step “ruling in” potential causes and “ruling out” others. It is arguable that “ruling in” a substance as the cause of an illness A. Nail down the diagnosis collapses both general and specific causation into a single step. How The plaintiff’s actual diagnosis can an expert rule in the should be the least controversial defendant’s product as a cause of part of the differential diagnosis the plaintiff’s disease unless the process. If the plaintiff does not expert can demonstrate that the have a solid, verifiable diagnosis, product can cause the disease? 57 his or her experts should not even Likewise, how can the expert rule in begin to address causation. the defendant’s product unless Still, in the same case, the plaintiff’s exposure or dose level plaintiff’s actual diagnosis may be was high enough for the disease to uncertain or non-specific. Tamraz occur? The challenge for the is an example. The plaintiff had defense lawyer is to identify and Parkinson’s, but the expert wanted separate the multiple components to call it “manganese-induced of the “ruling in” step. movement disorder.” When the diagnosis is uncertain, the defense 1. Get the expert to lawyer should be prepared to make commit to the legal a detailed record of each possible standard for causation diagnosis. It should be difficult (or impossible) for an expert to assess “General causation” and general causation or specific “specific causation” may be legal causation, or to rule in or rule out terms, but they are also terms that potential causes, if the diagnosis is toxicologists and medical experts uncertain or open to debate. understand. The defense lawyer Disagreement or uncertainty over should ask the expert to define the plaintiff’s diagnosis is a red flag general causation and specific for a Daubert challenge. causation. If the expert balks or claims not to know, the defense lawyer can ask: “Do you agree that in order to establish causation, you

57 As indicated above, some courts hold that a differential diagnosis only applies to specific causation and that general causation must be established first, before a differential diagnosis becomes relevant. Differential Diagnosis and Daubert 19

must first demonstrate that my the expert believes supports an client’s product can cause the association between the product plaintiff’s illness at some dose and the plaintiff’s condition. An level?” and “Do you agree that you expert who is attempting to rely on also need to show that my client a differential diagnosis may not be had a high enough exposure to able to identify epidemiology in cause the illness?” The case law support of his or her opinion. The arguably requires the expert to absence of epidemiological answer both questions in the evidence of an association should affirmative. If the expert says no, he be a key feature of a Daubert or Frye or she is out of sync with the law. If motion. he or she says yes, the expert has opened himself or herself up to 3. Ask about the Hill detailed questions on general and criteria and similar specific causation. standards

2. Know the epidemiology A properly trained toxicologist or epidemiologist should Before the deposition, the understand the Hill criteria and expert should have disclosed a similar methods for evaluating written report or disclosure multiple studies in order to providing the basis for his or her establish causation. The defense opinions. If that report discloses attorney should also learn and epidemiological evidence in understand the criteria. The support of the expert’s opinions, the defense lawyer should be prepared defense lawyer should read each to ask the expert to name each of study and be prepared to ask the the criteria and to describe in detail expert about the distinctions how he or she applied them. Most between the studies and the often, the expert’s answers will be plaintiff’s situation. The defense equivocal or vague. lawyer should also have a working A related technique is to ask the knowledge of any negative expert for any work papers or notes epidemiology so that the lawyer can which specifically demonstrate at least ask the expert to admit that how the expert applied the criteria there are studies which looked for and the weight or importance the the connection between the expert applied to each study. Ask if product and the plaintiff’s illness, the expert created a Hill criteria but didn’t find it. “scorecard” or “matrix.” The case At a minimum, the defense law does not appear to require such lawyer should ask the expert to detail, but the absence of such proof identify each primary study which 20 DEFENSE COUNSEL JOURNAL | JANUARY 2017

opens the expert up to criticism that reconstruction years or decades his or her work is not transparent. after the fact is usually fraught with speculation and unfounded and 4. Ask for the dose/ unproven assumptions. response evidence 5. Be alert to reliance on The case law generally “judgment” indicates that experts need not prove dose/response with While it is true that some courts mathematical precision, but some have allowed experts to rely on evidence of dose/response is “professional judgment” or required. The defense lawyer “professional experience” to should be prepared to ask: “How support a differential diagnosis much exposure to my client’s opinion, those decisions are not in product is necessary to cause tune with the prevailing case law on plaintiff’s illness?” If the expert has proving causation. By its nature, an answer to that question, the professional judgment is personal defense lawyer should ask for all to the expert, and arguably non- the evidence in support of that reproducible. answer and be able to question the If an expert attempts to rely on expert’s reliance on that evidence. judgment, the defense lawyer For example, if the answer involves should document the points in the animal research, the defense lawyer process where judgment came into should be able to ask for play and what parts of the information on how the expert traditional analysis the expert extrapolated from animal evidence replaced with judgment. Defense to human effects. The goal with this counsel should also ask the expert question is to set up a Joiner-type to admit that a similarly trained challenge. expert might arrive at a different Likewise, the defense lawyer judgment when faced with the same should ask for all of the information facts. in the expert’s possession regarding plaintiff’s actual exposure. Most 6. Other illnesses are not often, the exposure giving rise to causes the alleged affect happened in the distant past, and exposure data While building the detailed does not exist. The attorney should record of which potential causes document the absence of exposure the expert purported to rule in, the data and then probe any alternative defense lawyer should pay careful methods the expert used to attention to what items the expert evaluate exposure. Dose places on the list. Experts applying differential diagnoses have a Differential Diagnosis and Daubert 21

tendency to pad the “rule in” list with items that clearly do not apply. 7. A Material Safety Data Often this list includes alternative Sheet (MSDS) is not illnesses which could have caused proof of causation the plaintiff’s symptoms or condition. If it is clear from It is not uncommon for an plaintiff’s medical records that he expert to attempt to rely on an or she did not have the illness under MSDS as proof that the defendant’s consideration, it does not belong on product “could cause” one or more the list. In a toxic exposure case, the of the health effects set forth on the only items that should go on the list MSDS. A detailed review of the are other exposures or conditions reasons for including potential that could cause the plaintiff’s health effects on MSDSs is beyond illness and that the plaintiff clearly the scope of this article, but courts did have or could have had. have generally ruled that an expert Idiopathic origin should almost cannot use an MSDS as proof of always be on the list. As will be causation unless the expert discussed below, ruling out an understands and can explain the idiopathic cause is (and should be) scientific evidence used to compile much more difficult than ruling one the MSDS.58 in.

58 Mallozzi v. EcoSMART Techs., Inc., No. 11–CV–2884 (SJF)(ARL), 2013 WL 2415677, at *13 (E.D.N.Y. May 31, 2013); Moore, 151 F.3d at 278 (stating that an MSDS has limited scientific value when it is not known what tests were conducted in generating the MSDS); Turner, 229 F.3d at 1209 (stating that the product’s MSDS indicating that breathing dust may irritate the nose and throat and aggravate respiratory was not a sufficient basis for an expert opinion where the expert did not rely upon the MSDS, and “nothing in the record demonstrate[d] what scientific tests or information [the manufacturer] used to generate its MSDS”); Ingram v. Solkatronic Chem., Inc., No 04-CV- 0287, 2005 WL 3544244, at *6 (N.D. Okla. Dec. 28, 2005) (stating that expert’s reliance upon an MSDS was not reliable since the expert “knew nothing about the source of the information contained in the MSDS” and “[w]hen an expert purports to offer an opinion based upon his review of 22 DEFENSE COUNSEL JOURNAL | JANUARY 2017

C. Identify common “red ignoring the negative ones is flags” “cherry picking” and courts have refused to admit expert evidence The ruling in stage is a common employing this technique.59 place for experts to engage in some of the logical fallacies that courts 2. Post-hoc reasoning have identified as “red flags.” Some experts claim to rule in 1. Cherry picking substances based on the temporal connection between the exposure Negative epidemiology is as and the illness. That is, the expert important as positive will claim that he or she knows that epidemiology. The expert should the plaintiff was exposed (because be able to explain why negative the plaintiff said so), and that the epidemiology (i.e., studies which exposure was high enough to cause looked for a connection between the illness because the plaintiff got the exposure and the illness but did sick. This type of circular reasoning not find it) does not detract from from effects to cause should not the expert’s opinion. Relying on survive Daubert scrutiny. 60 only the positive studies while existing literature, it is . . . critical [that] the proposed expert carefully review the 59 Norris, 397 F.3d at 884; Adams v. Cooper methodology utilized by the scientist Indus. Inc., No. 03-476-JBC, 2007 WL conducting the study to ensure the quality 1805586, at *7 (E.D. Ky. June 21, 2007); In of the assumptions and data therein”); re Bextra & Celebrex Mktg. Sales Practices & Yates v. Ford Motor Co., 143 F. Supp.3d 386, Prods. Liab. Litig., 524 F. Supp.2d 1166, 390 (E.D.N.C. 2015) (determining that a 1176 (N.D. Ca. 2007); Newell Rubbermaid, court may refrain from treating an MSDS as Inc. v. Raymond Corp., 676 F.3d 521, 527 reliable until it is presented with scientific (6th Cir. 2012). evidence justifying the statements 60 See Nelson, 1998 WL 1297690, at *11 contained in the MSDS); Johnson v. Arkema, (stating that expert’s conclusion that Inc., 685 F.3d 452, 462-465 (5th Cir. 2012) plaintiffs’ PCB levels were high enough to (stating that an MSDS, without an cause their illness because they had the explanation of its scientific basis, is not illness was “circular reasoning without sufficient support for a causation opinion); basis” and was improper), aff’d, 243 F.3d Coastal Tankships, U.S.A., Inc. v. Anderson, 244, 254 (6th Cir. 2001) (“The magistrate 87 S.W.3d 591, 610-611 (Tex. App. 2002) judge properly rejected the circular (stating that an MSDS is of little value in reasoning that the plaintiffs must have been determining causation if there is no exposed to the PCBs because PCBs were evidence of what tests were conducted to present in the environment and plaintiffs compile the MSDS); Brookshire Bros., Inc. v. showed symptoms.”); Young v. Burton, 567 Smith, 176 S.W.3d 30, 35-39 (Tex. App. F. Supp.2d 121, 137 (D. D.C. 2008) (finding 2004) (stating MSDS is not reliable that expert’s methodology in diagnosing evidence that plaintiffs’ exposure caused “mold illness” was unreliable because his illness). among other things, “he used circular Differential Diagnosis and Daubert 23

3. Unique genetic law. The defense lawyer should susceptibility take advantage of that intersection to develop as detailed a record as An expert trying to establish possible on how the expert that a common exposure (i.e., assessed both general and specific vaccines) causes a relatively rare causation. The expert who is illness (i.e., ) needs to state seeking to avoid Daubert and Frye why all or most of the people scrutiny may attempt to evade exposed to the substance do not get questions by claiming that a the illness. Some experts solve this differential diagnosis does not problem by claiming that the involve issues such as epidemiology plaintiff must have had a unique and dose response. The defense genetic susceptibility to the alleged lawyer should understand that a ill effects of the product. 61 The significant number of reported science of genetics has advanced so decisions do require such an much in recent years, however, that analysis, even in the context of a any expert making such a claim differential diagnosis. It is should be required to provide important not to let the expert shut evidence that the plaintiff had or down the questioning, but rather to has a specific polymorphism that document all of the things the increases the risk of the disease at expert did to reach a conclusion and issue, and that the defendant’s all of the things the expert did not product increases the risk in people do. with that polymorphism. The “ruling in” step is the place where the differential diagnosis technique intersects most closely with existing Daubert and Frye case reasoning to work backwards from presumed that the plaintiff must have diagnosis to proof of exposure”); Mancuso v. somehow been exposed to a high enough Consol. Edison Co. of N.Y., 967 F. Supp. 1437, dose to exceed the threshold in order to 1450 (S.D.N.Y. 1997) (“As courts have have caused the , thereby recognized, it is improper for an expert to justifying his initial diagnosis”)), aff’d, 13 presume that the plaintiff “must have F.3d 1090 (7th Cir. 1994); Durden v. Sec’y somehow been exposed to a high enough of Dep’t of Health & Human Servs., No. 05- dose to exceed the threshold [necessary to 163V, 2007 WL 4962000, at *13 (Fed. Cl. cause the illness], thereby justifying his Sept. 26, 2007) (describing expert’s opinion initial diagnosis. This is circular reasoning.”) that “because cytokines cause immune (citing O’Conner v. Commonwealth Edison mediated disorders, and [the plaintiffs’ son] Co., 807 F. Supp. 1376, 1396 (C.D. Ill. 1992) has an immune mediated disorder, (stating that expert engaged in circular therefore, his disease process was triggered reasoning by presuming that plaintiff’s by cytokines” as “circular reasoning”). cataracts “were radiation induced, and then 61 Blackwell, 408 Md. at 613. 24 DEFENSE COUNSEL JOURNAL | JANUARY 2017

D. Collect detail on the should logically be all but rationale for “Ruling impossible. Out” Therein lies the opportunity for defense counsel to make a useful The “ruling out” portion of the Daubert record. The defense differential etiology technique has counsel should be prepared to no true analog in the Daubert case press the expert on why and how law. It is a unique aspect of the the expert knows that each item he differential diagnosis approach and or she “ruled in” did not in fact therefore poses special problems. cause the plaintiff’s illness. If the Courts have generally held that expert had a good reason to rule experts must “reliably” rule out some potential cause in, he or she causes other than the defendants’ should have an even better reason product in order to arrive at an to rule it out. The expert’s answers admissible differential diagnosis.62 to these questions have the The existing case law, however, potential to be unscientific and provides very little guidance as to circular. This is the place where how an expert should go about this defense counsel should make the step. record that the expert’s opinion is But “ruling out” should logically based on speculation. It is be much more difficult than “ruling important to be patient and to ask in.” Once an expert has ruled in a detailed questions about each potential cause by reference to potential cause and all of the medical or scientific literature, he reasons it was ruled out. or she should have a very good A common fallacy relied on by reason for ruling it back out again. plaintiff’s experts at this stage of the Further, identifying what may have differential diagnosis is to rule out caused an illness is a complicated, diseases or medical conditions that inherently uncertain process. the plaintiff undisputedly did not Determining what did not cause it have. While a using a

62 See Tamraz, 620 F.3d at 674; Pluck, 640 cause’” of plaintiff’s injury) (citing In re F.3d at 680 (ruling that expert “failed to Paoli, 35 F.3d at 759 (determining that ‘rule out’ alternative causes” of plaintiff’s where a defendant points to a plausible non-Hodgkin’s ); Lauzon v. Senco alternative cause and the doctor offers no Products, Inc., 270 F.3d 681, 694 (8th Cir. explanation for why he or she has 2001) (stating that expert needed to “be concluded that was not the sole cause, that able to explain why other conceivable doctor’s methodology is unreliable)); Hall, causes” of plaintiff’s illness “are 947 F. Supp. at 1414 (“General causation excludable”); Best, 563 F.3d at 179 (stating issues aside, an expert must rule out other that “the doctor must provide a reasonable potential causes of the patient's condition in explanation as to why ‘he or she has order for differential diagnosis testimony to concluded that [any alternative cause be admissible.”). suggested by the defense] was not the sole Differential Diagnosis and Daubert 25

differential technique to diagnose disease have an an illness will rule out diseases or unknown cause? medical conditions, an expert using  Would you agree that the technique to assess causation the cause of the disease should not be allowed to do that. is identified in only a The defense lawyer should be small number of cases? prepared to press the expert on the question of what exposures or risk In Tamraz, the court held that, factors are known to cause the when an idiopathic origin accounts plaintiff’s illness and how the for the vast majority of the cases of expert determined that the the disease, an idiopathic plaintiff’s illness was not caused by explanation is “impossible to ignore any of those risk factors or a and difficult to rule out.” 63 In combination of risk factors. McCarty v. Arch Wood Protection, Inc., 64 the district court excluded E. The special problem of the expert’s opinions because they unknown etiology admitted that all prior cases of plaintiff’s extremely The truth is, in most cases, no had been idiopathic. Because the one knows what caused a particular experts agreed that medical science person to develop a particular did not know the cause of plaintiff’s disease. The defense lawyer should illness, their conclusions – reached be prepared to explore the notion of through a differential etiology “unknown etiology,” using a few technique – that the defendants’ simple questions: product caused the illness, were nothing more than speculation.65  How many cases of the Whether failing to rule out an disease are diagnosed idiopathic origin for an illness will in the U.S. each year? result in the exclusion of the  In how many of those expert’s testimony will depend on cases is the cause how often the illness arises identified? idiopathically. That is, if a small  Would you agree that percentage of the cases of the most cases of the disease are idiopathic, the expert’s

63 Tamraz, 620 F.3d at 675. 64 No. CV 11-109-HRW, 2016 WL 1306067 (E.D. Ky. Mar. 31, 2016). 65 See also Henrickson, 605 F. Supp.2d 1142; Soldo v. Sandoz Pharm. Corp., 244 F. Supp.2d 434 (W.D. Pa. 2003); Nelson v. Am. Home Prods., 92 F. Supp.2d 954 (W.D. Mo. 2000); Anderson, 87 S.W.3d at 609. 26 DEFENSE COUNSEL JOURNAL | JANUARY 2017

failure to rule out an idiopathic medical cause and legal cause to the cause will likely not doom the court and to guide the court to the opinion because experts are not appropriate standard for ruling on generally expected to definitively the admissibility of causation rule out all potential causes.66 On opinions based on a “differential the other hand, if most cases of the diagnosis” or “differential etiology.” disease are idiopathic, the expert should have a very difficult time explaining how he or she ruled out an idiopathic origin.67

V. Conclusion

Both differential diagnosis in clinical practice and differential etiology in the courtroom seek to determine the “cause” of a person’s condition, and both use similar steps to do that. The similarities between the two processes, however, can sometimes be used to mask the very important distinctions between a medical cause and a legal cause. Courts have sometimes ignored or misunderstood the distinction and have admitted speculative causation opinions they should have excluded. A defense lawyer, however, should be prepared to explain the differences between

66 See Johnson v. Mead Johnson & Co., LLC, “[a]dmissible expert testimony need not 754 F.3d 557 (8th Cir. 2014) (“experts are rule out all alternative causes” of the not required to rule out all possible causes plaintiff’s disease); Luttrell v. Novartis when performing the differential etiology Pharm. Corp., 894 F. Supp.2d 1324, 1341 analysis”); Hammer v. Residential Credit (E.D. Wash. 2012) (“The Court Sols., Inc., No. 13 C 6397, 2015 WL 7776807, acknowledges that . . . it is not necessary to at *38 (N.D. Ill. Dec. 3, 2015) (stating that a rule out all other possible causes of “reliable expert should consider alternative [plaintiff’s injury] injury in order to survive causes, they do not require an expert to rule summary judgment.”), aff’d, 555 Fed. App’x out every alternative cause”); Perry v. 710 (9th Cir. 2014). Novartis Pharm. Corp., 564 F. Supp.2d 452, 67 See Tamraz, 620 F.3d 665; McCarty, 2016 469 (E.D. Pa. 2008) (stating that WL 1306067.