Merck Manual

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Stiff-Person Syndrome

(Stiff-Man Syndrome)


Michael Rubin

, MDCM, New York Presbyterian Hospital-Cornell Medical Center

Reviewed/Revised Apr 2022 | Modified Sep 2022

Stiff-person syndrome causes muscle stiffness that worsens gradually.

  • 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 some peripheral nerve disorders.

The cause of stiff-person syndrome may be an autoimmune reaction Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. What triggers an autoimmune disorder is not known. Symptoms vary depending... read more —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.

Symptoms of Stiff-Person Syndrome

In people with stiff-person syndrome, muscles of the trunk and abdomen gradually become stiffer and enlarge. Muscles of the arms and legs are affected less.

Usually, stiff-person syndrome progresses, leading to disability and stiffness throughout the body.

Diagnosis of Stiff-Person Syndrome

  • Electromyography

  • Blood tests

The diagnosis of stiff-person syndrome is suggested by symptoms. Tests are done to help confirm the diagnosis. They include electromyography Electromyography Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Imaging tests commonly used to diagnose nervous system (neurologic) disorders... read more Electromyography and blood tests to detect the antibodies that are present in many people with stiff-person syndrome.

Treatment of Stiff-Person Syndrome

  • Diazepam (a sedative) or another drug to relax the muscles

  • Immune globulin

  • Sometimes corticosteroids

  • Sometimes rituximab or plasma exchange

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 by vein (intravenously), may help relieve symptoms for up to a year.

If immune globulin does not help, rituximab (a drug that modifies the immune system's activity) or plasma exchange Plateletpheresis (platelet donation) In addition to normal blood donation and transfusion, special procedures are sometimes used. In plateletpheresis, a donor gives only platelets rather than whole blood. Whole blood is drawn from... read more , which involves filtering toxic substances (including the abnormal antibodies) from the blood, is sometimes tried.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Diastat, Dizac, Valium, VALTOCO
ED Baclofen, FLEQSUVY, Gablofen, Lioresal, Lioresal Intrathecal, LYVISPAH, OZOBAX, OZOBAX DS
RIABNI, Rituxan, RUXIENCE, truxima
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