Neonatal Myasthenia Gravis Clinical and Pathophysiological Aspects

Abstract

A small but significant percentage (10 to 20%) of babies born to myasthenic mothers are affected by transient neonatal myasthenia gravis (NMG), which is due to the transfer from the maternal circulation of antibodies directed against the acetylcholine receptor (AChR) at the motor endplate. A small amount NMG babies have a fetal involvement with hydramnios, arthrogryposis, and a very severe evolution. No correlation can be drawn between the severity, the duration, the clinical condition of the mother's illness and the clinical condition of the baby. On the day of birth, the level, the repertoire and the functional activity of anti-AChR antibodies are usually similar in mother and her baby (with or without NMG). Thus, mother and her infant show different susceptibility to the same immunological injury. After birth, the baby's anti-AChR antibodies clear in 1 to 5 months. NMG occurrence is on the whole correlated with a high amount of precipitating, modulating, and blocking anti-AChR antibodies. Furthermore, antibodies directed against the fetal form of AChR could be involved in NMG, particularly in the fetal form. The absence of NMG in the majority of newborn babies to MG mothers, some of them with high anti-AChR ab titer, is puzzling. After the birth of one NMG infant, the chance of subsequent children being similarly affected is high. The fetal forms are usually recurrent. The management of NMG involves meticulous survey of the baby initiated during the pregnancy (detection of reduced movements and hydramnios), and continued in an intensive care unit for a few days after birth because of a possible delayed onset.