Clinical, magnetic resonance imaging, and neuropathological features of suspected inborn methylmalonic aciduria in a domestic shorthair kitten.

A 10-month-old domestic shorthair kitten was evaluated for progressive neurological dysfunction characterized by ataxia, episodic opisthotonus, impaired vision, dysphagia and seizures. Clinicopathological findings included marked hypocobalaminemia and abnormal concentrations of urinary methylmalonic acid, methylcitrate, and propionylglycine. Magnetic resonance imaging revealed generalized cerebral and cerebellar atrophy, with mild ventriculomegaly. Despite dietary modification, cobalamin supplementation, antiepileptic therapy, neurological deterioration progressed, culminating in refractory seizures and euthanasia. Post-mortem examination revealed multiorgan and central nervous system changes, characterized by neuronal degeneration and necrosis, cortical atrophy, globular eosinophilic intracytoplasmic material within neurons and gliosis. Methylmalonic aciduria is a rare metabolic disorder resulting from defects in cobalamin metabolism or methylmalonyl-CoA mutase activity.