Transient Neonatal Myasthenia

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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 newborns5,7suggest 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