Diagnoses & Conditions

Stiff Person Syndrome (SPS)

Understanding SPS

Stiff-person syndrome (SPS) is believed to be an autoimmune disorder, which develops when the immune system malfunctions and creates antibodies that attack and cause damage to a part of the body. In most individuals with SPS, an enzyme in the brain called GAD, or glutamic acid decarboxylase, is attacked. This enzyme is important in the making of a neurotransmitter in the brain that causes nerve signals to send a message to the muscles to relax. Less commonly antibodies to amphiphysin may be present. Amphiphysin is a protein involved in the transmission of signals between nerve cells.

Symptoms of SPS

Symptoms of stiff-person syndrome (SPS) include progressive muscle rigidity in the trunk (torso) and limbs that occurs with muscle spasms. Spasms frequently occur in response to some stimulus, such as unexpected or loud noise, touch, cold environments, and other physical and emotional stressors. The rigidity, caused by contracted muscles, can interfere with posture, balance and walking. People with SPS become anxious by the increased rigidity, which also interferes with their ability to complete everyday tasks. Rigidity can be mild or so severe it causes pain and inability to walk.

Diagnosing SPS

Diagnosing stiff-person syndrome (SPS) is difficult because presenting symptoms can mimic other conditions such as Parkinson's, multiple sclerosis or anxiety. It may take years to definitively diagnose. There is also some thought that some forms of SPS may be so mild, they may simply be diagnosed as a back or leg strain.

Diagnostic testing may include:

  • Electromyography (EMG) to measure muscle activity.
  • Nerve conduction studies (NCS) to measure efficiency and speed of nerve signals.
  • Blood work to test for the anti-GAD or amphiphysin antibody that may be present in SPS.

Treating SPS

Treatment of stiff-person syndrome (SPS) may involve anti-seizure medications, muscle relaxants, anti-anxiety medications and/or immune globulin therapy administered into the blood stream intravenously (IVIG). IVIG treatment should result in decreasing the attack on self and increasing the amount of GAD or amphiphysin, allowing muscles to relax. Muscle rigidity will subside and function will improve. The physician will assess response to therapy and determine the length of therapy needed.


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The information provided on this website is not medical advice, nor is it intended to be a substitute for medical advice, diagnosis, and treatment. Always seek the advice of a physician or other qualified health provider with questions concerning a medical condition. Never disregard professional medical advice, or delay seeking it based on information provided on this website.