Stiff-person syndrome often occurs in people with type 1 diabetes, certain autoimmune disorders, or certain kinds of cancer.
Muscles gradually become stiffer and enlarge, starting in the trunk and abdomen but eventually affecting muscles throughout the body.
Doctors suspect stiff-person syndrome based on symptoms but use electromyography and blood tests to help confirm the diagnosis.
Treatment focuses on relieving symptoms and can include diazepam (a sedative), baclofen (a muscle relaxant), corticosteroids, and sometimes rituximab or plasma exchange.
Stiff-person syndrome (formerly called stiff-man syndrome) affects mainly the brain and spinal cord (the central nervous system), but it causes symptoms similar to those of neuromuscular junction disorders (disorders that affect the connection between nerves and muscles).
Stiff-person syndrome is more common among women and often occurs in people with type 1 diabetes, certain autoimmune disorders (such as thyroiditis), or certain kinds of cancer, including breast cancer (most commonly), lung cancer, kidney cancer, thyroid cancer, colon cancer, and Hodgkin lymphoma.
The cause of stiff-person syndrome may be an autoimmune reaction—when the body produces antibodies that attack its own tissues. In stiff-person syndrome, these antibodies attack nerve cells in the spinal cord that control muscle movement. Most people with stiff-person syndrome have antibodies that attack an enzyme called glutamic acid decarboxylase. This enzyme is involved in the production of a chemical messenger (neurotransmitter) that helps prevent nerves from overstimulating muscles. When less of this enzyme is produced, nerves overstimulate muscles, which become tight and stiff.
Sometimes the cause of stiff-person syndrome is unknown.
The diagnosis of stiff-person syndrome is suggested by symptoms. Tests are done to help confirm the diagnosis. They include electromyography and blood tests to detect the antibodies that are present in many people with stiff-person syndrome.
Treatment of stiff-person syndrome focuses on relieving symptoms. The sedative diazepam can consistently relieve the muscle stiffness. If diazepam is ineffective, other drugs, such as baclofen (a muscle relaxant), may be tried.
Immune globulin (a solution containing many different antibodies collected from a group of donors), given intravenously, may help relieve symptoms for up to a year.
Corticosteroids can help but, if taken for a long time, have many side effects.
If immune globulin does not help, rituximab (a drug that modifies the immune system's activity) or plasma exchange, which involves filtering toxic substances (including the abnormal antibodies) from the blood, is sometimes tried.