Chapter 43 Specific Diseases The only imaging modality of use for the diagnosis of CDS is MRI. Brain imaging of AD patients can be normal or may reveal brain atrophy, ventricular enlargement, and lesions in the medial temporal lobes of the cerebral cortex (Fig. 43-1). Age-related changes appreciated on MR imaging of the brain in CDS patients are primarily reflective of brain atrophy and include ventricular enlargement, widened and well-demarcated cerebral sulci, and diffuse and scattered areas of T2-hyperintensity in periventricular white matter. Although these are consistent findings associated with the aging brain, they may be found in older patients without evidence of CDS. The thickness of the interthalamic adhesion as measured on transaxial T1- and T2-weighted MR images was found to be significantly smaller in dogs with CDS compared with dogs without CDS (Fig. 43-2); an interthalamic adhesion thickness of 5 mm or less was found to be consistent with a diagnosis of CDS in dogs (Hasegawa et al, 2005). Hasegawa, D, Yayoshi, N, Fujita, Y, et al. Measurement of interthalamic adhesion thickness as a criteria for brain atrophy in dogs with and without cognitive dysfunction (dementia). Vet Rad Ultrasound. 2005;46:452. Mertens, M, Willard, MW, Miller, M, Fossum, TW. Diagnosis of congenital portosystemic shunts in miniature schnauzers seven years old or older (1997-2006). J Amer Anim Hosp Assoc. 2010;46:235. Reme, CA, Dramard, V, Kern, L, et al. Effect of s-adenosylmethionine tablets on the reduction of age-related mental decline in dogs: a double-blinded, placebo-controlled trial. Vet Ther. 2008;9:69–82. Degenerative Myelopathy Major differential diagnoses for DM are chronic type II disk protrusion and spinal neoplasia. Awano, T, Johnson, GS, Wade, C, et al. Genome-wide association analysis reveals a SOD 1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proc Natl Acad Sci USA. 2009;106:2794. Jones, JC, Inzana, KD, Rossmeisl, JH. CT myelography of the thoracolumbar spine in 8 dogs with degenerative myelopathy. J Vet Sci. 2005;6:341. Ischemic/Vascular Disease There are multiple potential causes for brain infarcts, including systemic hypertension (primary/essential hypertension or secondary to underlying disease such as chronic renal failure, hyperadrenocorticism, or pheochromocytoma), cardiac disease, hypercoagulability, increased blood viscosity (e.g., polycythemia vera, multiple myeloma), intravascular neoplasia (e.g., lymphoma, hemangiosarcoma), infectious disease, and atherosclerosis (e.g., associated with hypothyroidism, diabetes mellitus, or hyperlipidemia). In people with strokes, an underlying cause is not identified in about 40% of cases; these infarcts are termed “cryptogenic.” The percentage of cryptogenic strokes in dogs is believed to be similar to that in people. In contrast to humans, atherosclerosis appears to be rarely associated with canine brain infarcts; when it does occur in dogs, it is most likely to be associated with hypothyroidism. Brain infarcts in dogs are typically nonhemorrhagic and are most common in the cerebellum, cerebrum, and thalamic/midbrain regions. Multifocal brain infarcts have been reported but are comparatively uncommon. Cerebellar and cerebral infarcts tend to be territorial, involving the territories of large arteries such as the rostral cerebellar artery and middle cerebral artery, respectively. These territorial infarcts tend to primarily involve the gray matter with variable levels of white matter involvement. Thalamic/midbrain infarcts tend to be smaller lacunar lesions involving the smaller perforating arteries of this brain region. In one report, over half of the dogs with brain infarcts had an underlying metabolic disorder that could potentially lead to thromboembolic disease, the most common being chronic renal disease and hyperadrenocorticism (Garosi et al, 2005). Systemic hypertension was documented in nearly 30% of those dogs whose blood pressure was documented. In another study of cerebellar infarcts in dogs, systemic hypertension was identified in over 40% of those patients in which blood pressure was measured (Darrin et al, 2006). In the author’s experience there is usually an underlying disease present that could potentially explain the presence of hypertension in these dogs, with chronic renal disease and hyperadrenocorticism being the most common disorders.
Nonsurgical Disorders of the Brain and Spine
Cognitive Dysfunction Syndrome
Diagnosis
Diagnostic Imaging
References
Differential Diagnosis
References
General Considerations and Clinically Relevant Pathophysiology
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Nonsurgical Disorders of the Brain and Spine
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