Transient Neonatal Myasthenia
Transient neonatal myasthenia occurs in about 10% to 15% of infants born to myasthenic mothers and is due to transplacental transfer of circulating acetylcholine receptor (AChR) antibodies from the myasthenic mother to the fetus.
Symptoms appear within the first few hours of birth; however, occasionally onset may be delayed for three to four days. Typical clinical characteristics include feeding difficulty, generalized weakness and hypotonia, respiratory difficulties, fetal cry, facial weakness, and, less frequently, ptosis.The author prefers diagnostic confirmation by evaluating the response to edrophonium or neostigmine, with repetitive nerve stimulation studies performed at baseline and subsequent to infusion of the anticholinesterase agent. A response decrement with slow rates of stimulation (2-5 Hz) over a train of four to five stimuli may be repaired by the edrophonium (Tensilon) or neostigmine.
Treatment is largely supportive and the condition itself limiting, with resolution generally occurring within two to three weeks, although occasional cases may persist longer.