The networks of interwoven nerve fibers from different spinal nerves (plexuses) may be damaged by injury, tumors, collections of blood, or autoimmune reactions.

• Pain, weakness, and loss of sensation occur in all or part of an arm or a leg.
• Electromyography and evoked responses help doctors locate the damage, and magnetic resonance imaging helps locate the damage and identify the cause.
• Sometimes treating the disorder causing the problem improves nerve function.

A plexus is like an electrical junction box, which distributes wires to different parts of a house. In a plexus, nerve fibers from different spinal nerves (which connect the spinal cord to the rest of the body) are sorted. The fibers are recombined so that all fibers going to a specific body part are put together in one nerve. Damage to nerves in the major plexuses causes problems in the arms or legs that these nerves supply. The major plexuses are the brachial plexus, which is located in the neck and shoulders and distributes nerves throughout the arms, and the lumbosacral plexus, which is located in the lower back and pelvis and distributes nerves to the pelvis and legs.

Nerve Junction Boxes: The Plexuses Much like the electrical junction box in a house, a nerve plexus is a network of interwoven nerves. Nerve fibers from different spinal nerves are sorted and recombined in plexuses, so that all fibers going to a specific body part are put together in one nerve. Four nerve plexuses are located in the trunk of the body: The cervical plexus provides nerve connections to the head, neck, and shoulder. The brachial plexus provides connections to the chest, shoulders, upper arms, forearms, and hands. The lumbar plexus provides connections to the back, abdomen, groin, thighs, knees, and calves. The sacral plexus provides connections to the pelvis, buttocks, genitals, thighs, calves, and feet. Because the lumbar and sacral plexuses are interconnected, they are sometimes referred to as the lumbosacral plexus. The spinal nerves in the chest do not join a plexus. They are the intercostal nerves, which are located between the ribs.

Causes

The most common causes of damage are physical injury and cancer. An accident that pulls the arm or severely bends the arm at the shoulder may damage the brachial plexus (located near the shoulder). In newborns, the brachial plexus can be such damage during birth if the delivery requires pulling or other maneuvers. A fall can injure the lumbosacral plexus (located near the hip).

A cancer growing in the upper part of the lung can invade and destroy the brachial plexus. Or a cancer of the intestine, bladder, or prostate can invade the lumbosacral plexus. Other masses, such as a noncancerous (benign) tumor, an abscess, or a collection of blood (hematoma), may cause plexus disorders by putting pressure on a plexus.

Radiation therapy for breast cancer or diabetes, which can damage nerves throughout the body, may also damage nerves in a plexus.

Acute brachial neuritis (sudden malfunction of the brachial plexus) is probably caused by an autoimmune reaction—when the body produces antibodies that attack its own tissues. This disorder occurs primarily in men. It typically occurs in young adults but can occur at any age.

Symptoms

Malfunction of the brachial plexus causes pain, weakness, and loss of sensation in an arm. All or part of the arm (such as the forearm or biceps) may be affected. If the cause is an injury, recovery tends to occur slowly, over several months, although some severe injuries cause permanent weakness.

Acute brachial neuritis causes severe pain in the upper arms and shoulders. Usually, the arm becomes weak and reflexes are impaired as the pain resolves. Weakness develops within 3 to 10 days. Then people typically regain their strength over the next few months.

Malfunction of the lumbosacral plexus causes pain in the lower back and leg as well as weakness and loss of sensation in all or part of a leg (such as the foot or calf). Recovery depends on the cause.

Diagnosis

Doctors suspect that a plexus is involved when symptoms are located in a part of the body supplied by a specific plexus. The location of the symptoms indicates which plexus is affected.

Electromyography and nerve conduction studies can also help locate the damage (see Diagnosis of Brain, Spinal Cord, and Nerve Disorders: Electromyography and Nerve Conduction Studies). Magnetic resonance imaging (MRI) can help determine whether a cancer, another mass, or an injury is causing the plexus disorder.

Treatment

Treatment depends on the cause. Cancer near the plexus may be treated with radiation therapy, chemotherapy, or both. Occasionally, a cancer or another mass that is damaging the plexus must be removed surgically.

If diabetes is the cause, controlling blood sugar levels can help.

Doctors sometimes prescribe corticosteroids for acute brachial neuritis and other plexus disorders thought to be caused by an autoimmune reaction, but these drugs have no proven benefit. When an injury is the cause, time for healing may be all that is needed, but sometimes surgery is required.

Last full review/revision February 2008 by Michael Rubin, MD