A peer-reviewed version of this preprint was published in PeerJ on 13 April 2020.
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Dewey CW, Rishniw M, Johnson PJ, Davies ES, Sackman JJ, O’Donnell M, Platt S, Robinson K. 2020. Interthalamic adhesion size in aging dogs with presumptive spontaneous brain microhemorrhages: a comparative retrospective MRI study of dogs with and without evidence of canine cognitive dysfunction. PeerJ 8:e9012 https://doi.org/10.7717/peerj.9012 Presumptive spontaneous brain microhemorrhages in geriatric dogs: a comparative retrospective MRI study of dogs with and without evidence of canine cognitive dysfunction
Curtis W Dewey Corresp., 1, 2, 3 , Mark Rishniw 1 , Philippa J Johnson 1 , Emma S Davies 1 , Joseph J Sackman 2 , Marissa O'Donnell 2
1 Clinical Sciences, Cornell University College of Veterinary Medicine, Ithaca, New York, United States 2 Long Island Veterinary Specialists, Plainview, New York, United States 3 Rochester Veterinary Specialists and Emergency Services, Rochester, New York, United States
Corresponding Author: Curtis W Dewey Email address: [email protected]
The objective of this study was to compare specific brain MRI anatomic measurements between three groups of geriatric ( > 8yrs) dogs: 1) neurologically impaired dogs with presumptive spontaneous brain microhemorrhages and no clinical evidence of canine cognitive dysfunction 2) dogs with canine cognitive dysfunction 3) dogs without clinical evidence of cognitive impairment or abnormalities on neurologic examination (control dogs). MR images from 46 geriatric dogs were reviewed and measurements were obtained of interthalamic adhesion height (thickness) and mid-sagittal interthalamic adhesion area for all dogs, in addition to total brain volume. Interthalamic adhesion measurements, either absolute or normalized to total brain volume were compared between groups. Signalment (age, breed, sex), body weight, presence and number of SBMs, as well as other abnormal MRI findings were recorded for all dogs. All interthalamic adhesion measurement parameters were significantly (p<0.05) different between control dogs and affected dogs. Both dogs with cognitive dysfunction (12/13; 92 %) and dogs with isolated brain microhemorrhages had more microhemorrhages than control dogs (3/19; 16%). Affected dogs without cognitive dysfunction had more microhemorrhages than dogs with cognitive dysfunction. In addition to signs of cognitive impairment for the CCD group, main clinical complaints for SBM and CCD dogs were referable to central vestibular dysfunction, recent- onset seizure activity, or both. Geriatric dogs with spontaneous brain microhemorrhages without cognitive dysfunction have similar MRI abnormalities as dogs with cognitive dysfunction but may represent a distinct diseasecategory.
PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.27868v1 | CC BY 4.0 Open Access | rec: 19 Jul 2019, publ: 19 Jul 2019 1 ORIGINAL RESEARCH ARTICLE: Peer J
2 TITLE: PRESUMPTIVE SPONTANEOUS BRAIN MICROHEMORRHAGES IN
3 GERIATRIC DOGS: A COMPARATIVE RETROSPECTIVE MRI STUDY OF DOGS
4 WITH AND WITHOUT EVIDENCE OF CANINE COGNITIVE DYSFUNCTION
5 AUTHORS NAMES AND DEGREES:
6 Curtis Wells Dewey1,2,3, DVM, MS, CTCVMP, DACVIM (Neurology), DACVS; Mark
7 Rishniw1, BVSc, MS, PhD, DACVIM (Internal Medicine, Cardiology); Philippa J. Johnson1,
8 BVSc, CertVDI, DECVDI, MSc, MRCVS; Emma S. Davies1, BVSc, MSc, DECVN; Joseph
9 Sackman3, AA, BS; Marissa O’Donnell3, BS
10 AUTHOR AFFILIATIONS: Department of Clinical Sciences1, College of Veterinary Medicine,
11 Cornell University, Ithaca, NY; Rochester Veterinary Specialists and Emergency Services2,
12 Rochester, NY; Long Island Veterinary Specialists3, Plainview, NY
13 AUTHOR CONTACT INFORMATION:
14 CW Dewey: C4 169 Clinical Programs Center, Cornell University College of Veterinary
15 Medicine, Ithaca, NY 14853; [email protected]
16 M Rishniw: C2 015 Clinical Programs Center, Cornell University College of Veterinary
17 Medicine, Ithaca, NY 14853; [email protected]
18 PJ Johnson: Department of Clinical Sciences, Cornell University College of Veterinary
19 Medicine, 930 Campus Road, Box 25, Ithaca, NY 14853; [email protected]
20 21 ES Davies: C4 107 Clinical Programs Center, Cornell University College of Veterinary
22 Medicine, Ithaca, NY 14853; [email protected]
23 J Sackman: Long Island Veterinary Specialists, 163 South Service Road, Plainview, NY 11803;
25 M O’Donnell: Long Island Veterinary Specialists, 163 South Service Road, Plainview, NY
26 11803; [email protected].
27 CORRESPONDING AUTHOR: Curtis W Dewey: C4 169 Clinical Programs Center, Cornell
28 University College of Veterinary Medicine, Ithaca, NY 14853; [email protected]
29 DISCLOSURE STATEMENT: The authors have nothing to disclose
30 31 ABSTRACT
32 Objective: To compare specific brain MRI anatomic measurements between three groups of
33 geriatric (> 8yrs) dogs: 1) neurologically impaired dogs with presumptive spontaneous brain
34 microhemorrhages and no clinical evidence of canine cognitive dysfunction 2) dogs with canine
35 cognitive dysfunction 3) dogs without clinical evidence of cognitive impairment or abnormalities
36 on neurologic examination (control dogs). MR images from 46 geriatric dogs were reviewed and
37 measurements were obtained of interthalamic adhesion height (thickness) and mid-sagittal
38 interthalamic adhesion area for all dogs, in addition to total brain volume. Interthalamic adhesion
39 measurements, either absolute or normalized to total brain volume were compared between
40 groups. Signalment (age, breed, sex), body weight, presence and number of SBMs, as well as
41 other abnormal MRI findings were recorded for all dogs.
42 Results: All interthalamic adhesion measurement parameters were significantly (p<0.05)
43 different between control dogs and affected dogs. Both dogs with cognitive dysfunction (12/13;
44 92 %) and dogs with isolated brain microhemorrhages had more microhemorrhages than control
45 dogs (3/19; 16%). Affected dogs without cognitive dysfunction had more microhemorrhages
46 than dogs with cognitive dysfunction. In addition to signs of cognitive impairment for the CCD
47 group, main clinical complaints for SBM and CCD dogs were referable to central vestibular
48 dysfunction, recent-onset seizure activity, or both. Geriatric dogs with spontaneous brain
49 microhemorrhages without cognitive dysfunction have similar MRI abnormalities as dogs with
50 cognitive dysfunction but may represent a distinct disease category.
51 Keywords: Canine, dog, brain, microhemorrhage, cognitive, dementia, MRI, beta-amyloid,
52 Alzheimer’s, cerebral amyloid angiopathy 53 Introduction
54 Geriatric humans can suffer cerebral microbleeds, also referred to as cerebral microhemorrhages.
55 These microbleeds are often detected by MRI in patients with both Alzheimer’s disease or
56 cerebral amyloid angiopathy, although they occur in patients with stroke-like events without
57 evidence of dementia and, less commonly, as incidental findings.1-5 Cerebral amyloid angiopathy
58 refers to a specific brain vasculopathy of geriatric humans caused by the accumulation of β-
59 amyloid protein in vessel walls of brain arterioles and capillaries. Cerebral amyloid angiopathy
60 commonly causes spontaneous cerebral microbleeds in geriatric humans, either as an isolated
61 disorder or as a component of Alzheimer’s disease. Cerebral amyloid angiopathy possibly
62 represents a precursor stage to subsequent Alzheimer’s disease, because its presence in the
63 absence of dementia is a risk factor for developing Alzheimer’s disease.3-8 Microbleeds in
64 humans appear on MRI as circular, ovoid or “dot-like” parenchymal lesions, best identified with
65 T2* gradient echo or susceptibility-weighted MR sequences.1-5
66 Pathologists have identified both cerebral amyloid angiopathy and cerebral microbleeds in
67 geriatric dogs9-14, and clinicians have described putative microbleeds in geriatric dogs
68 undergoing MR imaging.15-17
69 We have observed geriatric dogs with and without evidence of cognitive dysfunction
70 occasionally presenting with recent onset seizure activity and/or central vestibular dysfunction.
71 The vestibular dysfunction in these dogs is generally much milder than that displayed in dogs
72 with “geriatric vestibular syndrome” and tends to improve more rapidly than the peripheral
73 disorder. These dogs typically exhibit varying numbers of punctuate lesions on MRI similar to
74 what is referred to as microbleeds or microhemorrhages in humans. As with human patients with 75 brain microhemorrhages associated with cerebral amyloid angiopathy, neurologists have not
76 identified any metabolic cause for the microhemorrhages in geriatric dogs.
77 We hypothesized that geriatric dogs with microhemorrhages without evidence of cognitive
78 dysfunction have a form of vascular -associated degenerative brain disease and that these dogs
79 have similar, abnormal, brain MRI features as dogs with cognitive dysfunction. More
80 specifically, we hypothesized that interthalamic adhesion measurements in affected dogs would
81 be smaller than that of aging geriatric control dogs (without evidence of encephalopathy or
82 cognitive dysfunction), similar to what previous investigators have documented in dogs with
83 cognitive dysfunction.18,19
84 85 Materials and Methods
86 We searched databases from three institutions (Cornell University Hospital for Animals, Long
87 Island Veterinary Specialists, and Rochester Veterinary Specialists and Emergency Services) for
88 brain MRI scans of geriatric (>8 yrs old) dogs with a diagnosis of cognitive dysfunction, geriatric
89 dogs with spontaneous brain microhemorrhages, and geriatric dogs with normal neurologic
90 examination findings (control dogs). Because few geriatric dogs without evidence of brain
91 disease undergo brain MRI, we acquired additional control geriatric brain MR images from two
92 sources: 10 mixed-breed retired sled dogs with normal neurologic examinations that had been
93 imaged as part of another study and 7 neurologically normal small-breed dogs whose owners
94 volunteered for a no-cost brain MRI prior to scheduled dentistry procedures.
95 We based our diagnosis of cognitive dysfunction on previously established historical and
96 clinical findings in association with characteristic MRI abnormalities.20-23
97 We defined spontaneous brain microhemorrhages using the same criteria as had been
98 previously proposed in humans and dogs; namely, as punctate areas of signal void in the brain
99 parenchyma of dogs (Figure 1) with no underlying metabolic reason (e.g., coagulopathy,
100 endocrine disorder, renal hypertension, vascular neoplasia, etc.) or associated intracranial reason
101 (e.g., tumor, inflammatory brain disease, etc.) for intracranial bleeding.5-7,17
102 All MRIs were performed under general anesthesia with one of four magnets: 1) 1.5 T
103 Siemens Avanto (Munich, Germany) 2) 1.5 T Toshiba Vantage Elan (Lake Forest CA, USA) 3)
104 3.0 T Philips Achieva (Nutley NJ, USA) or 4) 3.0 T GE Discovery MR750 (Chicago IL, USA).
105 Imaging sequences acquired included the following: sagittal T2-weighted; transverse T2-and T1-
106 weighted; transverse and dorsal plane T1-weighted post-gadolinium injection; transverse T2- 107 fluid attenuated inversion recovery (FLAIR); transverse T2* gradient-recalled echo (GRE); and
108 transverse susceptibility-weighted images (SWI). For the 1.5-T MRI units, measurement
109 parameters were as follows: slice thickness, 3.5 mm; slice gap, 3.5 mm; FOV, 185 mm; matrix
110 size of images, 480 x 480. For the 3.0-T MRI units, measurement parameters were as follows:
111 slice thickness, 2.0 mm; slice gap, 1.0-3.0 mm (depending on dog size); FOV, 1101 mm; matrix
112 size of images, 400 x 400.
113 For each dog, two investigators (JS & MO) measured the interthalamic adhesion height on
114 transverse T2-weighted images, as previously described (Figure 2).18 Additionally, these
115 investigators measured the cross-sectional area of the interthalamic adhesion on mid-sagittal T2-
116 weighted images (Figure 3), and total brain volume for each dog, using Mimics® software.
117 Volumetric measurements for total brain volume were performed as previously described.24
118 Both investigators used previously published anatomic landmarks for all measurements25 and
119 both were blinded to the clinical status of the dogs in the study. One investigator counted all
120 microhemorrhages evident on MR images for each dog (CD), based on transverse T2* gradient
121 echo or susceptibility-weighted sequences.
122 Statistical analysis
123 We used Kruskal Wallis tests, with subsequent multiple comparisons by the Conover method for
124 all comparisons described below. We did not correct for any experiment-wise error rate.
125 We first compared ages and body weights of the three groups of dogs to demonstrate similarity
126 of cohorts. 127 We compared the heights and areas of the interthalamic adhesions between the three groups of
128 dogs both as absolute values, and after indexing to total brain volume (under the assumption that
129 the height of the interthalamic adhesion would be proportional to the size of the brain).
130 Finally, we compared the number of microhemorrhages between the three groups of dogs.
131 132 Results
133 Our study consisted of 46 dogs: 19 control geriatric dogs, 14 dogs with spontaneous brain
134 hemorrhages without evidence of cognitive dysfunction, and 13 dogs with evidence of cognitive
135 dysfunction. Control dogs (10 yrs) were younger than affected dogs (13 yrs; P<0.0001).
136 Bodyweights of dogs in each group did not differ (P=0.9). Breeds represented in the control dog
137 group (CD) included mixed breed (11), Chihuahua (3), Dachshund (2) and one each of Yorkshire
138 terrier, Boston terrier and Maltese. There were 4 female spayed, and 2 each of female intact,
139 male castrated and male intact dogs in the control group. Breeds represented in the spontaneous
140 brain microhemorrhage group without cognitive impairment (SBM) included Shih tzu (2), mixed
141 breed (2) and one each of Maltese, Greyhound, Shetland Sheepdog, Boston terrier, Chihuahua,
142 Golden retriever, Pug, Yorkshire terrier and Bichon Frise. There were 8 female spayed and 6
143 male castrated dogs. Breeds represented in the cognitive dysfunction (CCD) group included Shih
144 tzu (2), Springer spaniel (2), and one each of Labrador retriever, Chihuahua, Miniature Poodle,
145 Shetland Sheepdog, Cockapoo, Samoyed, Miniature Schnauzer and mixed breed. There were 6
146 female spayed, 5 male castrated and 2 male intact dogs.
147 For the SBM group, the main clinical complaints included central vestibular dysfunction (9),
148 recent-onset seizures (3), or a combination of the two (2). For the CCD group, 5 dogs had
149 cognitive dysfunction alone, 5 also had recent-onset seizures and 3 also had central vestibular
150 dysfunction.
151 Control dogs had a taller sagittal interthalamic adhesion and a larger interthalamic adhesion area
152 than dogs with microhemorrhages without cognitive impairment and dogs with cognitive
153 dysfunction (P=0.0001 for both comparisons) (Figure 4 and Figure 5). The two groups of
154 abnormal dogs did not differ from each other (P>0.05). When indexed to total brain volume, 155 control dogs had a taller sagittal interthalamic adhesion than dogs with cognitive dysfunction, but
156 not dogs with microhemorrhages without cognitive dysfunction (P=0.005) (Figure 6). However,
157 when indexed to total brain volume, control dogs had a larger interthalamic adhesion area than
158 both groups of abnormal dogs (P=0.0001) (Figure 7). Again, the groups of dogs with
159 microhemorrhages without cognitive dysfunction and those with cognitive dysfunction did not
160 differ from each other (P>0.05).
161 Three control dogs (3/19; 16%) exhibited evidence of microhemorrhages, with 2 hemorrhages in
162 one dog and a single hemorrhagic lesion in the other two. Twelve of 13 dogs with cognitive
163 dysfunction (92%) had evidence of brain microhemorrhages. Control dogs had fewer
164 microhemorrhages than either group of abnormal dogs. Dogs with cognitive dysfunction had
165 fewer microhemorrhages than dogs without cognitive dysfunction (P<0.0001) (Figure 8).
166
167
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173
174 175 Discussion
176 Our study demonstrates that geriatric dogs with spontaneous brain microhemorrhages, but
177 without evidence of cognitive dysfunction have MRI features similar to dogs with spontaneous
178 brain microhemorrhages and cognitive dysfunction. Both groups of dogs with spontaneous brain
179 microhemorrhages had smaller interthalamic adhesions (both in height and area) than similarly
180 sized and aged control dogs. The interthalamic adhesion measurements did not differ between
181 the two neurologically affected groups of dogs. Somewhat surprisingly, dogs without cognitive
182 dysfunction had more microhemorrhages than dogs with cognitive dysfunction. Our
183 observations, coupled with the similarity in presenting clinical complaints (recent onset seizures,
184 vestibular dysfunction), suggest that dogs with microhemorrhages, with or without cognitive
185 dysfunction, might share pathophysiologic mechanisms and might be manifestations along a
186 spectrum of severity of a common disorder. However, the apparent absence of cognitive
187 dysfunction in the group of dogs with nearly twice the number of microhemorrhages as in the
188 dogs with cognitive dysfunction suggests that other factors might exist between the two groups.
189 Our results support the observations of previous investigators, who also found smaller
190 interthalamic adhesions in dogs with cognitive impairment than in control dogs.18,19 However,
191 decreases in interthalamic adhesion size are not specific for canine cognitive dysfunction, and
192 have been reported sporadically in other disorders that can cause brain atrophy.18 Because we
193 could not corroborate our findings with histopathology, we can only speculate that the lesions we
194 observed on MRI are indeed microhemorrhages. However, the shape, size and imaging
195 characteristics we identified are consistent with previous reports of microhemorrhages in both
196 humans and dogs.1-5,15-17 197 What could be causing microhemorrhages in dogs? Currently, we can only speculate about the
198 cause. Pathologists have described histopathologic features of cerebral amyloid angiopathy in
199 dogs, and have noted the presence of cerebral hemorrhages in these cases.10-13 Therefore, we can
200 reasonably hypothesize that the microhemorrhages in our cohorts might be the result of cerebral
201 amyloid angiopathy. Similar microhemorrhages in people are characteristic for cerebral amyloid
202 angiopathy, the diagnosis of which generally relies upon MRI findings and supporting clinical
203 features.5-8 Indeed, according to the Boston criteria for diagnosing human cerebral amyloid
204 angiopathy, supportive clinical data and MRI evidence of microhemorrhages, combined with the
205 absence of any other identifiable cause for hemorrhage, supports a diagnosis of “probable
206 cerebral amyloid angiopathy”.6,7,26-28
207 Could microhemorrhages in dogs be caused by cerebral amyloid angiopathy and could this, in
208 turn, lead to cognitive dysfunction? In humans, the relationship between cerebral amyloid
209 angiopathy and Alzheimer’s disease is well-established, but not straightforward; investigators
210 have identified cerebral amyloid angiopathy as a risk factor for development of Alzheimer’s
211 disease, and Alzheimer’s disease patients are commonly afflicted with concurrent cerebral
212 amyloid angiopathy.2-4,6-8 Furthermore, patients with Alzheimer’s disease or cerebral amyloid
213 angiopathy often display generalized cerebral atrophy.8,26 Despite the interrelationships between
214 these two amyloid-related brain disorders, cerebral amyloid angiopathy also occurs in people as
215 an isolated brain disorder, independent of Alzheimer’s disease. Additionally, cerebral amyloid
216 angiopathy can lead to dementia without concurrent development of Alzheimer’s disease.5-8,26
217 In both people and dogs, the amyloid deposits that occur in the walls of blood vessels differ from
218 those occurring around neurons in the brain parenchyma. Vessel-associated amyloid is a soluble
219 protein composed of 40 amino acids (Aβ1-40), whereas the more insoluble neuronal-associated 5-7,13,14,26,27 220 amyloid protein is typically 42 amino acids in length (Aβ1-42). There is evidence in
221 people that the ratio of Aβ1-40/Aβ1-42 in the brain might determine whether cerebral amyloid
222 angiopathy (higher ratio) or Alzheimer’s disease (lower ratio) is more likely to develop. In turn,
223 the expression of these proteins is thought to be influenced by specific gene mutations,
224 particularly those genes that deal with proteolytic cleavage of amyloid precursor protein; these
225 genes are variants of the apolipoprotein E gene.6,7,26,27
226 Similar to human amyloid-related brain disorders, studies in dogs suggest that different
227 molecular mechanisms may be involved in determining the preponderance of vascular-associated
10-13 228 Aβ1-40 versus parenchymal Aβ1-42 in an individual. One study demonstrated that brain
229 parenchymal Aβ1-42 deposits correlated with behavioral abnormalities, while vascular Aβ1-40
13 230 deposits were not. Canine cognitive dysfunction is considered by some to be the canine
231 analogue of Alzheimer’s disease, and has been described extensively as both a clinical and
232 pathologic entity.18-23,29-34 Unlike canine cognitive dysfunction, however, cerebral amyloid
233 angiopathy has not previously been described as a clinical entity in dogs, but only as a
234 pathological finding.9-14 We suspect that the microhemorrhages evident in both groups of
235 affected dogs reflect disorders of amyloid metabolism, a suspicion that will require further
236 inquiry. Unfortunately, because the dogs in our study were not euthanized at the time of
237 presentation (or shortly thereafter), we cannot confirm our suspicion of amyloid deposition,
238 either perivascularly or perineuronally, in affected dogs.
239 Putative cerebral microhemorrhages in dogs were described in a previous MRI-based study. 17
240 These investigators compared dogs with microhemorrhages to all dogs undergoing similar brain
241 MRIs, regardless of the indications for pursuing imaging. They found that dogs with cerebral
242 microhemorrhages were older and smaller, and presented more frequently for vestibular 243 dysfunction than the control group of dogs.17 Similar to this study, our populations of dogs with
244 microhemorrhages were primarily small-breed dogs; because we age-matched our controls as
245 much as possible, we could not comment on age distributions, although all of our dogs were
246 geriatric (>8 yo). It is also possible that smaller breeds would be expected to predominate
247 because they live long enough to develop degenerative brain disease, compared with larger dog
248 breeds.
249 Both cerebral amyloid angiopathy and cognitive dysfunction are well-established pathologies of
250 elderly dogs.9-14,18-23 Our study suggests that the dogs with spontaneous brain microhemorrhages
251 represent a distinct neurodegenerative brain disorder with some similarities to cognitive
252 dysfunction, but other features more reminiscent of cerebral amyloid angiopathy. Our suspicion
253 that these dogs have cerebral amyloid angiopathy will require future histopathologic examination
254 of brain tissue from patients with similar MRI abnormalities.
255 In addition to the lack of histopathologic correlation with the imaging findings in this study,
256 there are several other limitations to our investigation, most of which are a consequence of its
257 retrospective nature. We made the diagnosis of cognitive dysfunction in all dogs via historical
258 and clinical features consistent with cognitive impairment, combined with supportive MRI
259 findings. While this manner of diagnosing cognitive dysfunction is common practice and
260 adequate for a clinical diagnosis, it is likely to under-diagnose dogs with mild to moderate
261 cognitive impairment. There are a number of accurate behavioral test protocols for dogs that
262 provide more objective data regarding cognitive health.20,22,30 Although the dogs with isolated
263 microhemorrhages did not appear to have cognitive dysfunction, it is possible that they exhibited
264 some level of cognitive dysfunction that was not appreciable without specific behavioral testing.
265 Ten of the geriatric control dogs were kennel-housed and therefore not part of a home 266 environment, unlike the remainder of the control dogs and all dogs with microhemorrhages. As
267 such, cognitive dysfunction in some of these kennel-housed control dogs could have gone
268 unrecognized. Two of these dogs did have small interthalamic adhesions, despite being deemed
269 as cognitively normal. Ideally, all the control dogs would have been from home environments, in
270 which subtle behavioral changes could have been observed by owners. Although measuring
271 interthalamic adhesion thickness from a transaxial MR image slice is an accurate and easily
272 applicable clinical tool for the diagnosis of canine cognitive dysfunction18,19, some inherent error
273 in this method exists. The image slice that appears to have the largest interthalamic adhesion
274 measurement is chosen from the slices available, which introduces a level of variability in the
275 resultant data. Since the mid-sagittal interthalamic adhesion area is more consistent, this is likely
276 a more accurate mode of measuring the interthalamic adhesion.18 We found no differences
277 between the two groups of dogs with microhemorrhages, but the sample sizes were small and
278 might have failed to detect a difference.
279 Our main goal with this investigation was to compare MR imaging findings between two
280 abnormal geriatric groups of dogs: those with presumptive spontaneous brain microhemorrhages
281 and no cognitive impairment and those with evidence of canine cognitive dysfunction. We chose
282 our geriatric control dogs based upon a lower age limit of 8 years of age. Although this lower
283 limit is based on several reports dealing with canine cognitive dysfunction20-23,30 (one of the
284 affected dogs in our study, without cognitive dysfunction, was 8 years old), the definition of
285 what minimum age defines “geriatric” in dogs is somewhat arbitrary. Our control dogs were
286 younger than the affected dogs, but only one was 8 years old (and four were 9 years old). There
287 are several potential interpretations of this finding. One possibility is that both geriatric brain
288 disorders investigated in this report are more likely to occur with increasing age. This 289 phenomenon has been documented with canine cognitive dysfunction.20-23,35,36 In one study of
290 putative microhemorrhages in dogs17, affected dogs were significantly older than unaffected
291 dogs, but an increasing tendency for brain microhemorrhages to occur with aging has not yet
292 been established in this species. Another possibility is that a lower age limit of 8 years is too low
293 for a definition of “geriatric” in dogs. If this is the case, interthalamic adhesion measurements
294 may be less discriminative for degenerative brain pathology if the lower age limit for geriatric
295 control dogs is increased. In one study evaluating interthalamic adhesion thickness as an
296 indicator of cognitive dysfunction in dogs, 9 years of age was chosen as a lower limit for
297 defining geriatric status. These investigators found a significant difference in interthalamic
298 adhesion thickness between aging non-cognitively impaired and cognitively impaired older dogs.
299 They also found a significant difference in interthalamic adhesion thickness between older non-
300 cognitively impaired dogs and younger dogs (< 9 years of age). However, this difference was
301 negated when the interthalamic adhesion numbers were normalized to brain height.19 The overall
302 effect of aging on interthalamic adhesion parameters in successfully aging dogs needs to be more
303 fully evaluated.
304 Future investigation into geriatric dogs with spontaneous brain microhemorrhages will hopefully
305 include correlating MR imaging findings with histopathology, as well as more objective
306 assessment of cognitive status. In addition, comparing imaging features of larger cohorts of dogs
307 with and without cognitive dysfunction might help discern whether these entities are distinct
308 with respect to interthalamic adhesion measurements.
309 In conclusion, we have, for the first time, associated clinical signs in dogs, both with and without
310 cognitive dysfunction, with MRI evidence of microhemorrhages. Dogs with microhemorrhages
311 had smaller interthalamic adhesions than age-matched, weight-matched control dogs. Dogs 312 without cognitive had more hemorrhages than dogs with cognitive dysfunction, suggesting that
313 the cognitive dysfunction is not associated with hemorrhage number. Our data support, but do
314 not confirm the idea that spontaneous brain microhemorrhages in dogs might be a manifestation
315 of amyloid angiopathy.
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426 427 Figure Legends
428 Figure 1. Transverse T2* gradient echo MR images demonstrating typical appearance of
429 presumptive brain microhemorrhages. A-multiple microhemorrhages at the
430 diencephalon level. B-a single microhemorrhage in the left cerebellum.
431 Figure 2. Transverse T2-weighted MR image depicting method of measuring interthalamic
432 adhesion height (thickness).
433 Figure 3. Mid-sagittal T2-weighted image depicting method of measuring interthalamic
434 adhesion area.
435 Figure 4. Box and whisker plots of interthalamic adhesion thickness (height) for control
436 dogs, spontaneous brain microhemorrhage dogs without cognitive dysfunction
437 (SBM) and dogs with cognitive dysfunction (CCD).
438 Figure 5. Box and whisker plots of interthalamic adhesion area for control dogs,
439 spontaneous brain microhemorrhage dogs without cognitive dysfunction (SBM)
440 and dogs with cognitive dysfunction (CCD).
441 Figure 6. Box and whisker plots of interthalamic adhesion thickness (height) indexed to
442 total brain volume (TBV) for control dogs, spontaneous brain microhemorrhage
443 dogs without cognitive dysfunction (SBM) and dogs with cognitive dysfunction
444 (CCD).
445 Figure 7. Box and whisker plots of interthalamic adhesion area indexed to total brain
446 volume (TBV) for control dogs, spontaneous brain microhemorrhage dogs 447 without cognitive dysfunction (SBM) and dogs with cognitive dysfunction
448 (CCD).
449 Figure 8. Box and whisker plots of microhemorrhage numbers for control dogs,
450 spontaneous brain microhemorrhage dogs without cognitive dysfunction (SBM)
451 and dogs with cognitive dysfunction (CCD).
452
453
454 Figure 1
Transverse T2* gradient echo MR images demonstrating typical appearance of presumptive brain microhemorrhages. (A) Multiple microhemorrhages at the diencephalon level. Figure 2
Transverse T2* gradient echo MR images demonstrating typical appearance of presumptive brain microhemorrhages. (B) A single microhemorrhage in the left cerebellum.
Figure 3
Transverse T2-weighted image depicting method of measuring interthalamic adhesion height. Figure 4
Mid-sagittal T2-weighted image depicting method of measuring interthalamic adhesion area. Figure 5
Box and whisker plots of interthalamic adhesion thickness (height) for control dogs, spontaneous microhemorrhage dogs without cognitive dysfunction (SBM) and dogs with cognitive dysfunction (CCD). Figure 6
Box and whisker plots of interthalamic adhesion area for control dogs, spontaneous brain microhemorrhage dogs without cognitive dysfunction (SBM) and dogs with cognitive dysfunction (CCD) Figure 7
Box and whisker plots of interthalamic adhesion thickness (height) indexed to total brain volume (TBV) for control dogs, spontaneous brain microhemorrhage dogs without cognitive dysfunction (SBM) and dogs with cognitive dysfunction. Figure 8
Box and whisker plots of interthalamic adhesion thickness area indexed to total brain volume (TBV) for control dogs, spontaneous brain microhemorrhage dogs without cognitive dysfunction (SBM) and dogs with cognitive dysfunction Figure 9
Box and whisker plots of microhemorrhage numbers for control dogs, spontaneous brain microhemorrhage dogs without cognitive dysfunction (SBM) and dogs with cognitive dysfunction (CCD)