Disorders of Nerves and Nerve Roots

Facial palsy
The incidence of facial nerve palsy (Bell’s palsy) is substantially increased during pregnancy and the puerperium (as Bell himself described). The reason for this is not known. There have been no studies of treatment in this specific context but it is reasonable to treat promptly with prednisolone, beginning at 40 mg daily and reducing over a 2-week course.

Mononeuropathies
Carpal tunnel syndrome, due to compression of the median nerve in the wrist, is very common in pregnancy, characteristically causing pain and tingling in the hands at night and after use. Most cases can be managed with nocturnal wrist splints, although steroid injections into the carpal tunnel may tide the patient over into the puerperium, when symptoms usually remit.

Diuretics are of little value. Surgical decompression during pregnancy should be reserved for cases with severe pain, weakness, or wasting, when usually there have been symptoms either before pregnancy or early in the first trimester. In troublesome cases it is worth considering delayed surgery to prevent recurrence in subsequent pregnancies, which is common.

The lateral cutaneous nerve of the thigh can be compressed as it crosses the inguinal ligament. This is particularly common in the third trimester and causes tingling, hypersensitivity, or numbness in the midlateral thigh, which may be bilateral. Usually no treatment is required, but troublesome cases may respond to transcutaneous nerve stimulation or a local nerve block. Remission after delivery is the rule.

Lumbosacral root and plexus problems
Backache is very common in pregnancy, particularly in women with a past history of back pain or occupations that involve bending and lifting. It is traditionally blamed on changes in posture and hormonally mediated relaxation of spinal and sacroiliac joints. The pain is usually confined to the lumbar region but may radiate into the buttock or thigh. There may be tenderness over one or other sacroiliac joints. Radiological investigations are not needed if there are no abnormal neurological signs. Management is conservative.

Abrupt onset of pain that radiates below the knee with focal weakness, numbness, or reflex loss is most likely to be due to a prolapsed intervertebral disc. Provided that the signs are unilateral with no sphincter impairment, conservative management is again appropriate, with analgesia and advice to keep mobile. If this fails then magnetic resonance imaging is thought to be a safe method of investigation prior to consideration of lumbar microdiscectomy.

Obstetric nerve palsies are becoming less common with improvements in obstetric care, but still occur in cases of prolonged or complicated labour (for example due to cephalopelvic disproportion, dystocia, and primiparity), in difficult forceps deliveries, and as a result of traction or haematoma formation in caesarean section. Damage to the common peroneal nerve from incorrectly positioned leg holders is now rare.

The baby may compress the lower parts of the lumbosacral plexus during labour. This will typically give rise to focal neurological deficits depending on which parts of the plexus have borne the brunt of the pressure. Most commonly there is a unilateral footdrop, which may only become apparent when the mother starts to mobilize. Examination also reveals sensory loss that characteristically involves the dorsolateral foot and leg, distinguishing plexus damage from a common peroneal palsy where the sensory loss is confined to the dorsum of the foot. Compression of the upper lumbosacral plexus leads to weakness of iliopsoas as well as the quadriceps muscles, which distinguishes it from more distal damage to the femoral nerve. Both may give rise to sensory loss in the anteromedial thigh and loss or depression of the knee jerk. In most cases the prognosis is good, with spontaneous recovery over a couple of months. Particular care must be taken in subsequent deliveries to avoid further damage to the same nerve, as recovery after repeated injury will tend to be less complete.

Long, complicated, or instrumental deliveries may also damage the obturator or pudendal nerves. Obturator neuropathy leads to weakness of hip adduction and rotation, together with some sensory loss in the upper medial thigh. Pudendal nerve damage may be initially asymptomatic but probably contributes to the subsequent development of perineal descent and stress incontinence.

Generalized neuropathies
Chronic inflammatory demyelinating polyradiculoneuropathy can present or relapse during pregnancy, and can be treated with corticosteroids or (if necessary) intravenous immunoglobulin. The incidence of acute Guillain Barre syndrome is increased in the puerperium and can be managed in the usual ways.

The combination of the nutritional demands of pregnancy and hyperemesis gravidarum can lead to thiamine deficiency. This most commonly causes a subacute sensory neuropathy, but cases of acute Wernicke’s encephalopathy (with any combination of altered consciousness, ataxia, and ophthalmoplegia, leading if untreated to death) have been described. Both conditions respond promptly to parenteral thiamine 100 mg daily.

Pregnancy can precipitate relapse in acute intermittent porphyria: abdominal pain typically precedes autonomic and sensory neuropathy, sometimes with seizures and psychiatric disturbance. Finally, lepromatous neuropathies may present or deteriorate during pregnancy, making careful clinical supervision advisable.

Provided by ArmMed Media
Revision date: June 18, 2011
Last revised: by Dave R. Roger, M.D.