Neonatal myasthenia gravis: specific advantages of repetitive stimulation over edrophonium testing.

A premature infant with neonatal myasthenia gravis is presented to illustrate the utility of electrodiagnosis. The patient, born to a mother with myasthenia gravis, suffered additional problems, including hypoxia and subependymal hemorrhage which potentially contributed to hypotonia and poor respiratory effort, thus complicating the diagnosis. Standard testing with edrophonium originally was negative which cast doubt on the diagnosis; however, a repetitive motor nerve stimulation test demonstrated a significant decremental response which was consistent with neonatal myasthenia gravis. This decremental response was corrected following intravenous infusion of edrophonium. In the newborn with suspected myasthenia gravis, repetitive motor nerve stimulation may be a more reliable diagnostic procedure than the more frequently recommended pharmacologic tests. Use of this electrodiagnostic procedure in combination with pharmacologic testing may improve diagnostic accuracy in the premature infant and lead to earlier treatment.