Neuromuscular Thermography: an Analysis of Criticisms

Commentary Neuromuscular Thermography: An Analysis of Criticisms Jack E. Hubbard, Ph.D., M.D. Introduction method. Critics consign thermography to a role as an adjunctive test or screening method, or cite its supposed Technological assessments of the neuromuscular ap- nonspecific results and poor sensitivity. plications of thermography have been prepared recently by various organizations, including the American Med- Adjunctive Test ical Association (AMA), the Joint Council of State Neu- rosurgical Societies of the American Association of Some evaluations of thermography state that it is an Neurological Surgeons and the Congress of Neurolog- “adjunctive test” requiring “other procedures . to ical Surgeons, the Office of Health Technology Assess- reach a specific diagnosis.“g,27 The 1989 report9 from ment of the U.S. Department of Health and Human the Office of Health Technology Assessment (OHTA) Services, and the American ?Academy of Neurology of the U.S. Department of Health and Human Services, (AAN). Several of these evaluations, in part or in total, for example, concludes that “most investigators rec- have been critical of the medical usefulness of ther- ommend thermography only as a screening tool, as an mography. In addition, other published papers have adjunctive diagnostic device, and not as a primary di- unfavorably reviewed the clinical role of thermography. agnostic guide.” The OHTA report raises a question In the light of the literature as well as my own clinical about the difference between an “adjunctive test” versus experience as a neurologist, I will examine the significant a “primary diagnostic guide.” points and issues raised by this criticism, including clin- Ideally, a medical diagnostic test is designed to supply ical usefulness, abuse/misuse, published reports, and unique anatomical, physiological, or biochemical infor- community acceptance of thermography. In addition, I mation regarding body functioning. will confront contradictions in the criticism of ther- Therefore, it is difficult to separate an “adjunctive” mography as well as the role of political pressures in the from a “primary” test. The terms suggest that an “ad- assessment of thermography. junctive” test is subordinate to a “primary” method, but such a differentiation may not be obvious or even Clinical Usefulness valid. When an electromyographer performs a needle electrode examination, the resulting electrical signals All discussions of thermography agree that the pro- indicate only the physiologic state of the muscles tested. cedure is a non-invasive and safe method having no ad- If denervation potentials are recorded from specific verse biological effects. Further, most evaluations in- muscle groups, such as the lumbar paraspinals, pero- dicate that infrared thermal imaging is an accurate, sen- neous longus, anterior tibial, and posterior tibia1 mus- sitive method of displaying cutaneous temperature cles, the examiner makes certain assumptions and con- distribution. cludes the presence of an L5 radiculopathy. In this In my clinical experience and as reported by others, sense, the EMG is really an adjunctive test. The diagnosis thermal imaging of the cutaneous temperature distri- is made by the clinical skills and acumen of the electro- bution is an important aid in the diagnosis and man- myographer, not by the EMG. A radiologist examining agement of various neuromuscular causes of pain, such a head CT (computerized tomographic) scan observes as nerve root impingement,1-3 reflex sympathetic dys- a spherical, enhancing, well-contained mass with little trophy, 4-6 and other painful problems, such as myofas- edema, loosely attached to the inner table of the skull. cial injury’ and stress fracture.* However, reports critical A meningioma is diagnosed. The observations and con- of thermography question the clinical value of the clusions are based solely upon examining film showing differences in cranial tissue density as revealed by mul- tiple radiographic sections. The CT scan does not give From the Minneapolis Clinic of Neurology, Ltd., University of Minnesota School of Medicine. a tissue diagnosis. Since a specific diagnosis can be made 160 THERMOLOGY. 1990;3:160-165 © American Academy of Thermology only by pathological examination, is not the CT scan abnormality. As stated by Aminoff,16“in patients with “adjunctive”? In reality, is not all diagnostic testing central brainstem lesions, BAEPs may indicate that a “adjunctive” to the clinical presentation, which requires lesion is present but do not indicate its nature.” In this the interpretative skill of the reading or treating phy- respect, the BAEP is a screening tool, requiring further sician? If the above instances are indicative of “primary” diagnostic testing if it indicates abnormal findings. The tests, I submit that a thermographer who diagnoses a BAEP is an accepted procedure, and its use to screen cold extremity on a thermogram from a patient with for the presence of a lesion is valid. Similarly, since ther- chronic severe pain as reflex sympathetic dystrophy, is mography is a sensitive screen for radiculopathy’** or using a “primary diagnostic guide.” Findings of thermal other painful syndromes with a resultant vasomotor al- asymmetry are as diagnostic to the thermographer as teration, screening seems to be a reasonable, acceptable are muscle injury potentials to the electromyographer role for it. and tissue-density differences are to the radiologist. Poor Sensitivity Nonspecijc Results Several reports question the sensitivity of thermog- Closely associated with the concept of adjunctive test- raphy in radiculopathy, contending that thermal imaging ing is that of nonspecificity. For example, So et al.” does not give precise anatomical localization. The AAN characterized their findings as “nonspecific” in their report, 17for example, notes that “lack of precision of study of lumbosacral radiculopathy. Critics indicate that thermographic localization may have influenced other the reason that thermography is adjunctive is its limi- investigators to report that the test was not sensitive or g tation to “cutaneous temperature.“ They contend that specific.” So and his coworker Aminoff10report that thermographic results cannot be interpreted with cer- while their results “found thermography was similar in tainty because they are based upon a nonspecific func- sensitivity to conventional electrodiagnostic studies” tion, the temperature of the skin. correlating “well with the presence of clinical and EMG This point ignores the importance of vasomotor abnormalities,” they had “serious questions about the changes in response to neurovasomotor injury, a con- localizing value of thermography.” Despite the overall cept that was demonstrated as early as the 1940’s by positive results of their study, these authors concluded Richter, who revealed changes in skin resistance in re- that thermography was of “little diagnostic value.” 1 2 sponse to peripheral nerve injury. ’,‘ Richter’s work While the mechanism is unclear, thermography is a indicated that autonomic disruption in injury produces sensitive method for demonstrating the presence of a identifiable alteration of the sweat response, as measured radiculopathy. l-3 by galvanic skin resistance. Because of its effect on the onstrated with magnetic resonance imaging (MRI) the cutaneous microcirculation, sympathetic disruption in varying degrees and directions of herniated lumbar in- 3 a peripheral nerve1 causes clear thermal changes in the tervertebral disks and anatomical relationship to their 4 distribution field of the nerve.1 This thermal infor- autonomic nerve supply. The article includes a detailed mation is clearly revealed by thermography and is not discussion of the somatic and autonomic innervation of easily obtainable by any other method. An experienced the lumbar spine. This review supports the scientific thermographer is able to recognize the pattern and dis- basis by a vertebrogenic mechanism of the sympathetic tribution of vasomotor changes in response to nerve changes observed in the lower extremities as identified injury, leading to a differential diagnosis in specific sit- by thermal imaging. 15 uations in a given clinical context. At times, the distribution of the thermal abnormality does not fit precisely with the anatomical level of the Screening Method lesion. For example, a patient with a herniated L4-5 Some statements regarding the adjunctive role of disc may have a hypothermic response in the posterior thermography indicate that it should be considered leg, an Sl distribution. However, other techniques that “only” 9 as a screening tool, particularly in detection of measure physiologic responses also do not always have a radiculopathy. This wording minimizes its clinical clear anatomical correlation. Evoked response studies, value. Other diagnostic methods are considered helpful such as the BAEP, for example, are sometimes abnormal because of their ability to document the existence of a at a level or side that does not correlate with an ana- problem without supplying any further information. For example, evoked potentials, such as brainstem auditory cussed by Aminoff, l6 and he concluded that the “main evoked potentials (BAEP), provide physiologic infor- value of the technique is to establish that the lesion exists mation regarding the integrity of central neural path- rather than to define its precise location,” It seems in- ways, but they do not indicate the nature of the possible consistent that the same individual

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