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Peripheral Neuropathy

The signs and symptoms of neuropathy consist of sensory and motor phenomena in a peripheral nervous system distribution. The neuropathy may involve a single nerve, such as the peroneal nerve after compression at the knee; multiple distal nerves symmetrically, such as with distal axonal polyneuropathy; or multiple individual nerves asymmetrically, such as with mononeuritis multiplex. Patients may complain of numbness, tingling, pain, burning, loss of sensation, a cold sensation, altered sensation ("sock around the foot," "walking on pebbles" or hypersensitivity) and muscle weakness.

If the hands are involved, the patient may be unable to button a shirt. In the lower extremities, early symptoms include an ill-defined unsteadiness. Physical examination reveals reduced positional sense; decreased pinprick, temperature and vibratory perception; muscle weakness, and atrophy.

The most common type of polyneuropathy is a chronic predominantly sensory (large and small fiber) symmetric distal polyneuropathy. By the time sensory disturbances reach the upper shin, the fingers are usually involved. A typical stocking-and-glove pattern of sensory loss ensues. The first motor symptom is an inability to walk on the heels. Over time, an obvious footdrop may develop. This type of neuropathy has a large number of potential causes. However, in an estimated 30 percent of cases, no specific cause can be identified, and the diagnosis of a chronic idiopathic axonal neuropathy is made. In the United States, the most common causes of neuropathy are diabetes mellitus and alcohol abuse, but worldwide, leprosy is the most common cause of polyneuropathy.

CAUSES OF POLYNEUROPATHIES

Systemic Disorders. Polyneuropathy can complicate a variety of systemic disorders (Table 6). By far the disease most frequently associated with neuropathy is diabetes mellitus. There are an estimated 16 million persons with diabetes in the United States, 10 percent of whom experience symptomatic neuropathy. The most prevalent neuropathy in these patients is a symmetric distal.

Other common neuropathies in persons with diabetes include entrapment neuropathies. Truncal radiculopathy, isolated or multiple mononeuropathy and diabetic amyotrophy are much less common in this patient population. Diabetic amyotrophy is a highly painful, subacute, unilateral, proximal lumbosacral radiculoplexopathy that usually resolves spontaneously.

Rheumatologic Diseases. The most important neuropathy associated with rheumatologic disease is a mononeuritis multiplex caused by vasculitis of the nerves. Isolated peripheral nerve vasculitis, a mononeuropathy of subacute onset with severe burning dysesthetic pain, weakness and sensory loss, can occur in this setting. Multiple nerve involvement leads to patchy deficits in upper and lower extremities. This feature may be a presenting symptom of polyarteritis nodosa, or it may accompany other systemic vasculitic disorders, such as rheumatoid arthritis, Sjogren's disease or systemic lupus erythematosus.

Sometimes, a confluent polyneuropathy with only mild asymmetry creates a confusing diagnostic picture. An electromyogram (EMG) and nerve and muscle biopsies are essential to establish the diagnosis and should be rapidly obtained if there is strong suspicion of mononeuritis multiplex. Aggressive treatment with corticosteroids and cyclophosphamide (Cytoxan, Neosar) can produce full recovery. Without treatment, severe disability or death from systemic complications can occur. Patients should be tested for anti-neutrophil cytoplasmic antibodies(ANCA), which are seen in Wegener's granulomatosis and occasionally in peripheral nerve vasculitis. In addition, patients may have an elevated sedimentation rate, positive ANA and anti-SS-A and anti-SS-B antibodies, as in systemic lupus erythematosus and Sjogren's syndrome.

Nutritional Deficiency, Drugs and Toxins. Most neuropathies associated with nutritional deficiencies, drugs or toxins affect distal nerves, and the largest and longest fibers are the first affected. Alcohol abuse is a frequent cause of this type of neuropathy. Neuropathy typically progresses only minimally if the patient stops drinking. It is important to recognize vitamin B12 deficiency because this disorder can cause neuropathy as well as myelopathy.