JPC SYSTEMIC PATHOLOGY
Signalment (JPC 151004): 3-year old Charolais bull
HISTORY: Presented for a two-month history of chronic posterior paresia. Clinical examination showed right hock stiffness with right leg mobility reduction.
HISTOPATHOLOGIC DESCRIPTION: Cerebellum with brainstem: Multifocally and randomly within the cerebellar white matter and scattered randomly throughout the white matter of the brainstem, there are numerous, up to 50 um in diameter, round to oval, acellular, eosinophilic, granular plaques. Markedly hypertrophic glial cells are often present adjacent to plaques (presumed oligodendrocytes). The adjacent neuropil occasionally contains eosinophilic, up to 6 um, swollen, degenerate axons within dilated myelin sheaths (spheroids) and mild increased vacuolation (spongiosis). Within the meninges is granular brown black pigment (melanin).
MORPHOLOGIC DIAGNOSIS: Cerebellum and brainstem, white matter: Eosinophilic plaques, multifocal, severe, chronic, with axonal degeneration, mild spongiosis and gliosis, Charolais, bovine.
ETIOLOGIC DIAGNOSIS: Idiopathic leukodystrophy (oligodendroglial dysplasia/dysmyelination)
CONDITION: Progressive ataxia of Charolais cattle
· Unique heritable disease in Charolais cattle due to oligodendrocyte dysplasia which leads to dysmyelination that results in progressive ataxia
· Affects both sexes equally with onset from 6 months to 2 years of age
· Affects purebred Charolais and ¾ crossbred Charolais cattle
· Slow, progressive disease
· Heritable defect of oligodendroglial production and maintenance of myelin sheaths in paranodal areas; thought to be autosomal recessive
· Nodes of Ranvier are wide due to failure of oligodendoglia to ensheathe the anodal axon as it grows longitudinally resulting in abnormalities of impulse conduction
· Dysplasia is not considered to be due to a defect in the production of myelin, but rather of failure to ensheathe properly
TYPICAL CLINICAL FINDINGS:
· Progressive onset beginning with hind limb weakness and ataxia leading to subsequent recumbency
· Collapse of one hind limb with a tendency to fall to one side is a consistent finding
· Head bobbing when excited
· Irregular, pulsatile micturition in females
· Mentation and muscle tone are normal
TYPICAL GROSS FINDINGS:
· No gross lesions
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Multiple discrete, ovoid, pale, eosinophilic, granular to amorphous, noncellular plaques that measure 30-80 um in diameter in the white matter
· Located mainly in the cerebellum, optic nerve, optic tract, internal capsule, corpus callosum, lateral lemniscus, medial longitudinal fasciculus and pontine decussation
· Plaques may be traversed by axons that have little to no myelin
· Widened nodes of Ranvier
· Paranodal whorls of myelin that originate from hypertrophied oligodendrocytes
· Enlarged oligodendrocyte cell bodies and increased numbers of mitochondria
ADDITIONAL DIAGNOSTIC TESTS:
· LFB (Luxol-fast blue) to demonstrate accumulation of myelin
· Bielschowsky silver stain to demonstrate axons within tangled mat of myelin
· Definitive diagnosis is solely by histopathologic examination
· Plaques are distinctive
· Reported in Charolais cattle and two bullmastiff dogs (lesions in the brainstem and spinal cord)
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