Myasthenia Gravis in the Cat

Myasthenia gravis (MG) was diagnosed in four cats--one had an apparently congenital form and three had the acquired autoimmune form. All four cats were examined because of episodes of weakness including gait abnormalities, voice change, neck ventroflexion, and regurgitation. Palpebral reflexes were absent in all cats. Administration of edrophonium chloride resulted in transient resolution of clinical signs in all four cats. Three cats were tested for the presence of serum autoantibodies against acetylcholine receptor (AChR) by radioimmunoassay. Two cats with acquired MG had anti-AChR antibody titers of 10.5 and 96.8 nmol/l (normal, less than or equal to 0.03 nmol/l). Antibodies were not detected in the cat with presumptive congenital MG. All four cats were treated with pyridostigmine bromide. Two cats with acquired MG were euthanatized because of clinical deterioration. The third cat with acquired MG has been asymptomatic since 2 months after diagnosis. The cat with presumed congenital MG is alive 3 years after diagnosis.