Case Studies

 Case 5.2 Myasthenia gravis and neonatal myasthenia gravis

A 21-year-old woman was referred to a neurology clinic with a 1-month history of double vision, difficulty swallowing and weakness in her upper arms. These symptoms were mild or absent in the morning and tended to worsen through the day. When she was seen towards the end of an afternoon neurology clinic she was found to have a bilateral ptosis and disconjugate eye movements that could not be ascribed to any individual cranial nerve lesion. Her upper limb power was initially normal but deteriorated with repeated testing. An intravenous injection of edrophonium, a short-acting cholinesterase inhibitor, completely abolished the neurological signs but her eye movements deteriorated again 30min after the injection. A clinical diagnosis was made of myasthenia gravis. Subsequent blood testing showed the presence of a high level of antibodies against the acetylcholine receptor.

She was treated with oral cholinesterase inhibitors with some improvement. However, 1 month later she deteriorated and corticosteroids were introduced with no improvement. A computed tomography scan of her thorax showed no evidence of a thymoma but she was nevertheless referred to a thoracic surgeon for thymectomy as this can sometimes induce remission in myasthenia even in the absence of a thymoma. A small thymic remnant was removed and she recovered uneventfully and was able to withdraw from all medication without deterioration in her symptoms. Acetylcholine receptor antibody levels fell but remained detectable. One year later, she became pregnant and after an uneventful 41-week pregnancy she delivered a 4-kg male infant. There were immediate concerns about the baby who failed to make adequate respiratory efforts and who appeared limp and hypotonic. The baby was intubated and ventilated on the neonatal intensive care unit. In the light of the mother's history, a provisional diagnosis of neonatal myasthenia gravis was made, although care was taken to exclude other causes of neonatal respiratory insufficiency such as maternal analgesia with pethidine, hypoglycaemia and sepsis. A cranial ultrasound showed no evidence of bleeding or other pathology. Subsequent testing of a blood sample taken from the umbilical cord showed low levels of acetylcholine receptor antibody. The baby needed ventilation and feeding via a nasogastric tube for 3 days at which time the ventilation was successfully withdrawn. There were some initial feeding problems due to difficulty sucking and swallowing but these resolved over the next 48h. The child's subsequent development has been entirely normal. The mother also remains well.