Background: Myasthenia gravis, an autoimmune disease of young women, is due to the dysfunction of neuromuscular transmission. The newborn of a myasthenic mother inconstantly presents a transitory neonatal myasthenic syndrome. Maternal aggravation, or even myasthenic crisis with respiratory failure, can occur in the first three months post-partum.
Case report: Mrs. S., para two without appreciable medical history, delivered normally a boy weighing 4 kg with an Apgar score of 10/10. At 3 h of life the newborn was admitted to the neonatal care unit for grunting and axial hypotonia. Diagnoses of maternal-fetal infection and fetal distress were excluded. The dissociated pattern of neurological disorders (refusal to drink, axial hypotonia, hypomimia, but good contact and normal alertness) led to search for neuromuscular causes or poison. Myasthenia gravis was then considered and confirmed by maternal electromyography, allowing the diagnosis of transient neonatal myasthenia gravis and early diagnosis and treatment of the maternal myasthenic crisis in a specialized care unit. The outcome of both mother and child was favorable under treatment.
Conclusion: Lack of maternal myasthenia gravis history should not result in excluding the diagnosis of transitory neonatal myasthenia gravis when evocative neonatal neurological signs are present. The symptomatology in the newborn may indeed reveal maternal myasthenia gravis, allowing an early diagnosis in both the mother and the newborn.