Transient neonatal myasthenia gravis is a rare form of myasthenia gravis (MG) that typically affects 10–20% of babies born to mothers with MG, including those with minimal or no disease symptoms. It is one of three types of MG that may be seen in children; the other two are juvenile MG and congenital MG.
Causes
MG is an autoimmune disease in which the body mistakenly produces antibodies — called autoantibodies — that attack and damage acetylcholine receptors and other proteins involved in nerve-muscle communication. Over time this communication impairment causes muscles to lose their ability to contract and progressively weaken.
During pregnancy, the mother’s autoantibodies can be transferred to her unborn child through the placenta, resulting in the destruction of acetylcholine receptors in the developing fetus. It is not clear why only some babies born to mothers with MG develop transient neonatal MG. Some scientists believe it may be due to specific autoantibody characteristics that differ between individuals.
While disease severity in the mother does not appear to dictate disease severity in her baby, the child’s risk of developing transient neonatal MG as well as its severity have been associated with higher levels of maternal autoantibodies.
Mothers with active disease are more likely to give birth to babies with this form of MG. However, infants with transient neonatal MG also may be born to mothers displaying few or no MG symptoms, including those in remission.
Women with MG who have had their thymus gland surgically removed are at a lower risk of giving birth to infants with transient neonatal MG. This most likely is because thymus removal surgery helps lower the production of MG autoantibodies that potentially could be passed on to the developing fetus.
Symptoms
Infants with this condition have difficulties feeding and sucking, cry weakly, display a lack of facial expression, and often have problems breathing. They may 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 MG display symptoms within the first 24 hours after birth. In some rare cases, infants may start showing signs of the disease while still in the womb. Mothers may feel reduced fetal movement or have excessive amniotic fluid — the fluid that surrounds the fetus. That condition, known as polyhydramnios, is a result of the fetus being unable to swallow properly due to muscle weakness. Because of their limited movement, newborns also are at risk of developing joint contractures (stiffer connective tissues that limit range of motion), a condition known as arthrogryposis multiplex congenita.
Treatment and prognosis
Babies with transient neonatal MG often recover naturally within a few weeks or months, as maternal autoantibodies gradually disappear on their own.
However, some babies may need mechanical ventilation to help them breathe, or nutritional support (tube feeding or special formulas) due to swallowing issues. Some infants may need to be treated with acetylcholinesterase inhibitors, such as Mestinon (pyridostigmine).
Notably, infants with transient neonatal MG are not at a higher risk of developing MG later in life.
Last updated: Nov. 12, 2021
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