Hyperthyroidism and myasthenia gravis with features of Eaton-Lambert syndrome.

In a 50-year-old man with hyperthyroidism and myasthenic weakness electrophysiologic phenomena similar to Eaton-Lambert syndrome were seen in classical myasthenia gravis. The orbicularis oculi showed an abnormally small muscle action potential in response to nerve stimulus and unusual facilitation of the response with activity. These signs are compatible with Eaton-Lambert syndrome, but the findings obtained from the adductor pollicis were typical of classical myasthenia. A possible common basis for hyperthyroidism and such an electrophysiologic complexity of transmission failure was considered as a pathogenic hypothesis.