Neuromuscular Junction Disorders: Peripheral Nerve Disorders: Merck Manual Home Edition


	Sections		Brain, Spinal Cord, and Nerve Disorders

	Chapters		Peripheral Nerve Disorders

Neuromuscular Junction Disorders

Nerves connect with muscles at the neuromuscular junction. There, the ends of nerve fibers connect to special sites on the muscle's membrane called motor end plates. These plates contain receptors that enable the muscle to respond to acetylcholine, a chemical messenger (neurotransmitter) released by the nerve to transmit a nerve impulse across the neuromuscular junction. After a nerve stimulates a muscle at this junction, an electrical impulse flows through the muscle, causing it to contract.

Did You Know...

Nerve gases used in chemical warfare interfere with communication between nerves and muscles.

Overactive Nerves: Two Syndromes

Sometimes nerves repeatedly send electrical impulses to muscles, resulting in overstimulation. Overstimulation is thought to be a factor in S

tiff-person syndrome and Isaac's syndrome.

Stiff-person syndrome: This syndrome is more common among women and often occurs in people with diabetes or certain kinds of cancer, including Hodgkin lymphoma (Hodgkin's disease).

The cause may be an autoimmune reaction—when the body produces antibodies that attack its own tissues. Antibodies to an enzyme called glutamic acid decarboxylase are present, but whether they cause the symptoms is unknown.

Muscles of the trunk, abdomen, and legs gradually become stiffer and enlarge. Muscles of the arms, head, and neck are affected less.

The sedative diazepam can consistently relieve the muscle stiffness. Plasmapheresis, in which toxic substances are filtered from the blood, is sometimes tried but often without success. Without treatment, the disorder progresses, leading to disability and stiffness throughout the body.

Isaac's syndrome: This rare disorder has no known cause. It often occurs in people with cancer.

Muscles, particularly those in the arms and legs, continually twitch, moving like a bag of worms. This symptom is called myokymia. The hands and feet may intermittently have spasms and cramps. Muscle stiffness is common. Sweating may be increased.

Symptoms can be relieved by carbamazepine or phenytoin, both of which are anticonvulsants.

Disorders in which the neuromuscular junction malfunctions include myasthenia gravis (see see Peripheral Nerve Disorders: Myasthenia Gravis), botulism (see see Peripheral Nerve Disorders: Botulism), and Eaton-Lambert syndrome (see see Peripheral Nerve Disorders: Eaton-Lambert Syndrome). In addition, many drugs (including very high doses of some antibiotics), certain insecticides (organophosphates), curare (an extract from plants formerly placed on the tip of some poison darts and used to paralyze and kill), and the nerve gases used in chemical warfare can cause the neuromuscular junction to malfunction. Some of these substances prevent the normal breakdown of acetylcholine after the nerve impulse has been transmitted to the muscle.

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