Myasthenia Gravis Associated with Diphenylhydantoin Therapy For Epilepsy

Abstract
SUMMARY: A young woman with epilepsy developed myasthenic symptoms while taking diphenylhydantoin. The clinical, electromyographic and pharmacologic findings were consistent with myasthenia gravis. Symptoms of myasthenia ceased on withdrawal of the drug, and recurred on readministration, with little apparent relationship to serum phenytoin levels. This unusual effect is discussed with reference to the known effects of diphenylhydantoin at the neuromyal junction.