Transient neonatal myasthenia gravis is a rare form of myasthenia gravis that typically affects 10–15% of babies born to mothers who have myasthenia gravis, including those who are symptomatic. Symptoms usually resolve.
What causes transient neonatal myasthenia gravis?
Myasthenia gravis is an autoimmune disease in which the body mistakenly produces antibodies (called autoantibodies) against acetylcholine receptors; these receptors are important in allowing nerves to stimulate muscle contraction and movement. The autoantibodies destroy acetylcholine receptors, leading to the characteristic symptoms of muscle weakness.
During pregnancy, the mother’s autoantibodies can be transferred to her unborn child, resulting in the destruction of fetal acetylcholine receptors. It is not clear why only some babies born to mothers with myasthenia develop transient neonatal myasthenia gravis. Some scientists think that it may be due to specific autoantibody characteristics that differ between individuals.
Symptoms of transient neonatal myasthenia gravis
Infants with this condition have difficulties feeding and sucking, cry weakly, display a lack of facial expression, and often have problems breathing. They may also be ‘floppy’ (hypotonic), with their elbows and knees hanging loosely at their sides, as their muscles are too weak to allow them to bend their limbs.
Most babies with transient neonatal myasthenia gravis display symptoms within a few hours to 24 hours after birth. In some rare cases, infants may start showing signs of transient neonatal myasthenia gravis while still in the uterus. Mothers may feel reduced fetal movement or have excessive amniotic fluid (fluid that surrounds and cushions the fetus), a condition known as polyhydramnios, as a result of the fetus being unable to swallow properly due to muscle weakness. Because of their limited movement, newborns are at risk of developing joint contractures (stiffer connective tissues that limit range of motion), a condition known as arthrogryposis multiplex congenita.
Risk and severity
While disease severity in the mother does not appear to dictate disease severity in her baby, the child’s risk of developing transient neonatal myasthenia gravis and the condition’s severity is associated with higher levels of maternal autoantibodies. Infants in future pregnancies are also at risk.
Babies with this form of myasthenia gravis are more common to mothers who experience a disease episode during pregnancy; however, some mothers may have the condition but not display any symptoms. Women with myasthenia gravis who have had their thymus gland surgically removed are at a lower risk of giving birth to infants with transient neonatal myasthenia gravis.
Treatment and prognosis
Babies with transient neonatal myasthenia gravis often recover with treatment in a few weeks or months, as maternal autoantibodies disappear on their own. However, some babies may need mechanical assistance (a ventilator) to help them breathe or nutritional support (such as tube feeding or special formulas) for problems with swallowing. Some infants may also need to be treated with acetylcholinesterase inhibitors, a medication that increases the levels of acetylcholine (a chemical that stimulates acetylcholine receptors).
Infants with transient neonatal myasthenia gravis are not at a higher risk of developing myasthenia gravis later in life.
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