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Introduction

A wide range of neurological problems occasionally complicate pregnancy and the puerperium. Pre-existing neurological diseases, such as epilepsy and myasthenia gravis, sometimes become more troublesome or, like myotonic dystrophy, pose obstetric difficulties. New neurological disorders can occur, ranging from diseases of the peripheral nerves and muscles that are relatively common but generally benign, to diseases of the central nervous system that are rare but potentially life-threatening. In all these situations the presence of the fetus influences management.

Disorders of muscle and neuromuscular transmission

Muscle disorders
Muscle cramps, particularly on waking, are extremely common in the third trimester. They are almost never a symptom of serious neurological disease and often respond to calcium supplements. Restless legs syndrome, in which there is a feeling of discomfort in the legs that is relieved by movement, is also common, especially on retiring to bed.

It may respond to correction of underlying anaemia (particularly if this is due to folate or iron deficiency); otherwise management in pregnancy is aimed at promoting the rapid onset of sleep, for example by reducing caffeine intake. Drug treatment (with levodopa, clonazepam, or codeine) is best avoided. Polymyositis, although rare in young women, can deteriorate during pregnancy. Treatment with corticosteroids is thought to be safe, as is azathioprine if another immunosuppressive agent is necessary.

Most of the congenital myopathies and muscular dystrophies, apart from myotonic dystrophy, cause no special problems in pregnancy unless they are of sufficient severity to compromise ventilation, either because of respiratory muscle weakness or associated scoliosis. Such cases should ideally be assessed in a specialist unit prior to pregnancy because the cardio-respiratory demands of pregnancy, combined with the splinting effect of the fetus on the diaphragm, can lead to ventilatory failure and a temporary need for mechanical ventilation.

Myotonic dystrophy
Myotonic dystrophy is an autosomal dominant disorder due to an expanded triplet repeat in the myotonin protein kinase gene. The expansion tends to increase during transmission from mother to child, so that a mildly affected or asymptomatic mother may have a severely affected fetus. This probably accounts for the excess of polyhydramnios and perinatal death. The myotonia affects the smooth muscle of the uterus, prolonging labour and increasing the risk of postpartum haemorrhage because of uterine inertia. Moderately affected mothers may also develop symptoms of cardiomyopathy during labour.

Myasthenia gravis
Myasthenia gravis deteriorates, improves, and remains stable during pregnancy in roughly equal proportions of patients, but the response is neither predictable nor reproducible in subsequent pregnancies. It deteriorates during the puerperium in about half of all patients, an effect that may also occur after abortion.