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 diazepamSome Trade Names
DIASTAT VALIUM
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 carbamazepineSome Trade Names
TEGRETOL
or phenytoinSome Trade Names
DILANTIN
, both of which are anticonvulsants.