Sciatica is a form of peripheral neuropathy. It occurs when there is damage to the sciatic nerve, located in the back of the leg. This nerve controls the muscles of the back of the knee and lower leg and provides sensation to the back of the thigh, part of the lower leg and the sole of the foot. Incomplete damage to the sciatic nerve may appear identical to damage to one of the branches of the sciatic nerve (tibial nerve dysfunction or common peroneal nerve dysfunction).
 

A problem in a single nerve group, such as the sciatic nerve, is classified as a mononeuropathy. The usual causes are direct trauma (often due to an injection into the buttocks), prolonged external pressure on the nerve, and pressure on the nerve from nearby body structures. It can also be caused by entrapment -- pressure on the nerve where it passes through a narrow structure. The damage slows or prevents conduction of impulses through the nerve.
 

The sciatic nerve is commonly injured by fractures of the pelvis, gunshot wounds, or other trauma to the buttocks or thigh. Prolonged sitting or lying with pressure on the buttocks may also injure it. Systemic diseases, such as diabetes, can typically damage many different nerves, including the sciatic nerve. The sciatic nerve may also be harmed by pressure from masses such as a tumor or abscess, or by bleeding in the pelvis.
 

Treatment is aimed at maximizing mobility and independence. The cause of the nerve dysfunction should be identified and treated as appropriate. In some cases, no treatment is required and recovery is spontaneous.
 

Conservative treatment is usually appropriate if there was sudden onset, minimal sensation changes, no difficulty in movement, no history of trauma to the area, and no evidence of degeneration of the nerve axon.

Surgical removal of lesions that press on the nerve, such as a herniated disc, may relieve symptoms. In cases of severe injury to the nerve, such as laceration, recovery may be not possible or may be limited.
 

Injections can be used to reduce inflammation around the nerve. Over-the-counter or prescription analgesics may be needed to control nerve pain.
Various other medications may reduce the stabbing pains that some people experience, including phenytoin, carbamazepine, or tricyclic antidepressants such as amitriptyline. Steroids may help with nerve inflammation related to a herniated disc. Whenever possible, their use should be avoided or minimized to reduce the risk of medication side effects.
 

Physical therapy exercises may be appropriate for some people to maintain muscle strength. The use of braces, splints, orthopedic shoes, or other appliances may help compensate for lost or impaired function. Vocational counseling, occupational therapy, occupational changes, job retraining, or similar interventions may be recommended.

Peripheral neuropathy describes damage to the peripheral nerves, the vast communications network that transmits information from the brain and spinal cord to every other part of the body. It may be caused by diseases of the nerves or as the result of systemic illnesses. Many neuropathies have well-defined causes such as diabetes, uremia, AIDs, or nutritional deficiencies. In fact, diabetes is one of the most common causes of peripheral neuropathy.

Other causes include mechanical pressure such as compression or entrapment, direct trauma, penetrating injuries, contusions, fracture or dislocated bones; pressure involving the superficial nerves (ulna, radial, or peroneal) which can result from prolonged use of crutches or staying in one position for too long, or from a tumor; intraneural hemorrhage; exposure to cold or radiation or, rarely, certain medicines or toxic substances; and vascular or collagen disorders such as atherosclerosis, systemic lupus erythematosus, scleroderma, sarcoidosis, rheumatoid arthritis, and polyarteritis nodosa. A common example of entrapment neuropathy is carpal tunnel syndrome, which has become more common because of the increasing use of computers. Although the causes of peripheral neuropathy are diverse, they produce common symptoms including weakness, numbness, paresthesia (abnormal sensations such as burning, tickling, pricking or tingling) and pain in the arms, hands, legs and/or feet. A large number of cases are of unknown cause.

Source NIH