NEUROMUSCULAR DYSFUNCTION IN 5 DOGS WITH ACQUIRED MYASTHENIA-GRAVIS AND PRESUMPTIVE HYPOTHYROIDISM

An association between immune-mediated thyroid disorders and acquired myasthenia gravis (MG) is recognized in humans. A similar association has been suggested in dogs. Five dogs were presented because of variou s degrees of neuromuscular dysfunction; each had clinical signs and ra diographic findings consistent with megaesophagus. A positive serum ac etylcholine (ACh) receptor antibody level confirmed MG in each dog. Tw o of the five dogs had clinical evidence of a peripheral polyneuropath y; a common peroneal nerve biopsy demonstrating demyelination and axon al necrosis confirmed the diagnosis of a neuropathy in one of these do gs. A third dog had evidence of a polymyopathy, which was confirmed wi th electromyography and muscle biopsy. Hypothyroidism was presumptivel y diagnosed in all five patients based upon clinical signs, a resting serum thyroid hormone (T-4) level, and a thyroid stimulating hormone ( TSH) response test. In two of the dogs, further support for the diagno sis of hypothyroidism was suggested by resolution of clinical signs sh ortly after beginning thyroid hormone supplementation. The cases prese nted in this report suggest an association between hypothyroidism and acquired myasthenia gravis exists in dogs.