Transient Neonatal Myasthenia

Abstract

SOME 15% of infants born to mothers with myasthenia gravis develop respiratory and feeding difficulties and often more generalized weakness, which responds to cholinergic drugs.¹Symptoms appear within 72 hours of birth and persist for several days to three months.²This form of myasthenia does not recur later in life.³The implication is that a factor influencing neuromuscular transmission (NMT) crosses the placenta, and that this factor, or its effect persists for many weeks without leaving a permanent defect.⁴ There are two accounts of electromyographic (EMG) studies of such infants.^5,6Studies of NMT in normal newborns^5,7suggest that their neuromuscular junction functions with smaller reserves than the adult. Trains of repetitive stimuli are poorly sustained, and recovery after a train is delayed. We have conducted serial EMG studies in an infant with the syndrome, an unaffected infant of a myasthenic mother, and three