Simpson K, Battersby I, Lowrie M.
Presenting signs and initial investigations: An 8-year-old female spayed British shorthair cat was presented with a history of waxing and waning neurological signs. Neuroanatomical localisation was consistent with a diffuse forebrain disease. Blood ammonia concentration was increased. Abdominal ultrasonography and a bile acid stimulation test were normal. Magnetic resonance imaging (MRI) revealed hyperintense, bilaterally symmetrical, diffuse lesions on T2-weighted sequences, predominantly, but not exclusively, affecting the grey matter. Serum cobalamin (vitamin B(12)) concentration was low. Hypocobalaminaemia resulting in a urea cycle abnormality was considered a likely cause of the hyperammonaemia. Treatment: Daily cobalamin injections resulted in a rapid clinical improvement. Eight weeks into treatment neurological examination was unremarkable and there was complete resolution of the MRI lesions. Clinical importance: This is the first reported case of acquired feline hypocobalaminaemia resulting in an encephalopathy. Additionally, this case is unique in describing reversible brain MRI abnormalities in a cobalamin-deficient companion animal.