The advantages of electrodiagnosis in a premature infant with neonatal myasthenia gravis are proposed by the Dept of Rehabilitation Medicine, Children’s Hospital and Medical Center, Univ of Washington School of Medicine, Seattle, WA. The infant, born to a mother with myasthenia, suffered hypoxia and subependymal hemorrhage which probably contributed to the hypotonia and poor respiratory effort. Testing with edrophonium, 0.1 mg/kg IV demonstrated no clinical improvement, whereas repetitive motor nerve stimulation testing showed a significant decremental response consistent with a diagnosis of neonatal myasthenia gravis. The decremental response was corrected following IV infusion of edrophonium 0.15 mg/kg. Pyridostigmine in a dose of 8 mg/kg/day resulted in clinical improvement of respiratory and muscular activity, and the infant was weaned from assisted ventilation at 27 days of age. He was discharged at 41 days of age on pyridostigmine therapy. The authors conclude that repetitive motor nerve stimulation may be a more reliable diagnostic procedure than edrophonium IV in the newborn with suspected myasthenia gravis. [1]

COMMENT. The value of electrodiagnostic tests in the differential diagnosis of the hypotonic infant is demonstrated in these 2 case reports. Neonatology texts often recommend edrophonium as the test of choice in neonatal myasthenia gravis. The above experience indicates that the pharmacological test alone may not be as sensitive as repetitive nerve stimulation in the newborn with multiple problems. Ultrasonography is an additional technique of potential value in the work up of the hypotonic infant. Heckmatt JZ and Dubowitz V of Hammersmith Hospital, London, have introduced the method for the differentiation of congenital muscular dystrophy and non-neuromuscular cases of hypotonia. [2]