Stiff person syndrome

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at December 2, 2016
StartDiseasesStiff person syndrome

Stiff person syndrome (SPS) is a rare neurological disorder that causes episodes of muscular rigidity and painful muscle spasms. SPS occurs in about one in every one million people. It is most often found in middle-aged people, and it affects about twice as many women as it does men. It can affect any person of any age or gender and may also be referred to as stiff man syndrome (SMS), Moersch-Woltman syndrome, focal stiff person syndrome, stiff limb syndrome, jerking stiff person syndrome, or progressive encephalomyelitis with rigidity and myoclonus (PERM).


Definition & Facts

Muscle rigidity caused by stiff person syndrome ebbs and flows, often improving and then becoming worse again. The spasms may occur randomly or they might be triggered by external events like physical contact, psychological stress, sudden noises, or bright lights.

The affected person may have extreme sensitivity to light, touch, and sound. In some persons the disease affects only one area of the body, while in others it can be widespread affecting the brainstem and spinal cord. It is a progressive disease that, if untreated, can affect a person's ability to walk and to perform mundane daily tasks.

There are variations of SPS such as stiff-limb syndrome which affects only one limb. There is another paraneoplastic variant that is associated with breast cancer. The paraneoplastic version of SPS usually affects the neck and arms more than other versions of the disease and it can be more painful than the other versions. 

Symptoms & Complaints

The primary symptoms of SPS are muscle rigidity accompanied by muscle spasms. The severity of the symptoms can vary greatly from one person to the next, but it is possible to stabilize the symptoms through medication.

Symptoms typically begin with muscle stiffness, aches, and pains in the lower back and neck. As the disease progresses over a period of months or years, it may also begin to affect the shoulders, hips, and legs. In some cases, one side is affected more than the other which leads to an awkward, stiff gait.

The condition can cause outward curving of the spine (kyphosis) or inward curving of the spine (lordosis) which can result in either a hunched posture or an arched back. The condition can sometimes spread to the arms and face as well.

Leg spasms can result in falls or other accidental injuries. Spasms in the abdominal muscles can affect the person's eating habits and result in unexplained weight loss. Muscle spasms in the chest or respiratory system can be life-threatening and the patient may require the help of a ventilator to breathe.

Spasms may last anywhere from a few minutes to hours at a time. In more severe cases, the person affected may need to use a walker or wheelchair, and the ability to engage in everyday activities can be affected.


The cause of stiff person syndrome is unknown, although some studies suggest that it may be an autoimmune disorder caused by antibodies attacking healthy cells. Tests of affected persons have found antibodies that attack glutamic acid decarboxylase (GAD). GAD is a protein found in nerve cells that is key in the synthesis of gamma-aminobutyric acid (GABA). GABA helps to control muscle movement throughout the body.

The theory is that the affected person's immune system is inexplicably attacking the nerve cells which results in a shortage of GAD proteins and therefore a shortage of GABA as well. The shortage of GAD and GABA then causes the muscle rigidity and muscle spasms.

The cause of SPS, however, is still unknown. Some individuals with SPS do not have the antibodies that attack GAD which means there must be a different cause at least for those individuals. In others, researchers have found antibodies that attack amphiphysin, another protein that helps to transmit signals between nerve cells. 

Diagnosis & Tests

Stiff person syndrome is typically diagnosed by its symptoms, and tests can then be done to confirm the diagnosis and rule out other possibilities. An affected person can be screened for the presence of antibodies to GAD or antibodies to amphiphysin either of which indicates the presence of SPS.

An electromyography (EMG) test can detect the continuous muscle activity that is a characteristic of SPS. SPS is often associated with other autoimmune diseases such as diabetes mellitus, thyroiditis, vitiligo, and pernicious anemia.

Treatment & Therapy

There is no cure for stiff person syndrome, but the symptoms can be managed with medications and therapies. Benzodiazepines can be prescribed to relieve an affected person's muscle stiffness and muscle spasms. In some individuals, anti-seizure medications have also been effective.

Immunoglobin therapy (IVIG) is a therapy that is sometimes used to treat SPS. IVIG is a therapy most often used in the treatment of autoimmune disorders where the patient receives an infusion of antibody mixtures that contain antibodies taken from the plasma of blood donors. IVIG can have serious side effects, and it is known to have caused renal dysfunction, acute renal failure, osmotic nephrosis, and even death. Studies have shown, however, that it is effective in relieving the symptoms of SPS.

Plasmapheresis is a procedure sometimes used in treatment of SPS. It involves removing blood from the person with SPS, separating the blood cells from the plasma, replacing the plasma with new plasma that has been donated, and then replacing the new blood into the patient. The effect is the removal of unwanted substances like toxins from the person's blood. Use of artificially created antibodies such as rituximab may also prove to be effective in treatment of SPS. 

Prevention & Prophylaxis

There is no known method for the prevention of stiff person syndrome. It can, however, be important to prevent a flare-up of the symptoms at critical times such as when an affected person is undergoing surgery or other stressful medical procedures.

A prophylactic course of IVIG, or injection of healthy antibodies, prior to a medical procedure may prevent an occurrence of SPS during the procedure and any resulting complications. Use of diazepines for sedation prior to medical procedures may also help to prevent an occurrence of SPS symptoms during the procedure.