What Is Stiff Person Syndrome?

Stiff person syndrome (SPS), also called Moersch-Woltmann syndrome, is a rare nervous system disorder that causes muscle stiffness and spasms. Though the cause isn't known, research suggests that SPS is also an autoimmune disorder, and people with it often have other autoimmune disorders such as type 1 diabetes, vitiligo, or thyroiditis as well.

Stiff person syndrome affects females more often than males. It most often begins between the ages of 30 and 60 but can also appear in children and older adults. It is not known exactly how many people have it, but one estimate is one case per million people.

This article provides an overview of the symptoms, causes, diagnosis, and treatment of stiff person syndrome.

Symptoms of Stiff Person Syndrome

Symptoms of SPS may include:

• Muscle stiffness in the trunk and limbs: This causes back stiffness or pain and a stiff-legged walk. The stiffness may come and go at first but eventually becomes constant and tends to worsen over time gradually. Without treatment, it may become disabling.
• Severe muscle spasms in the arms and legs: These may occur randomly or be triggered by stimuli such as loud noises, cold, touch, or stress.
• Problems with posture, including a curved lower back (lordosis) or hunched upper back
• Joint deformity in severe cases
• Falling during sudden muscle spasms, which may lead to injury
• Weight loss if spasms of abdominal muscles affect appetite
• Problems breathing, sometimes life-threatening, if spasms affect respiratory muscles
• Depression, anxiety, and phobias: These may be the result of living with the symptoms but may also be an effect of the way the condition affects brain signals.

Causes

Stiff person syndrome is believed to be an autoimmune condition, in which the immune system attacks healthy cells. In SPS, antibodies produced by the immune system may attack an enzyme in the central nervous system called glutamic acid decarboxylase (GAD).

This enzyme helps produce a protein called gamma-aminobutyric acid (GABA), which regulates nerve cells. GABA effectively "slows down" nerve signals. It's believed that SPS causes a lack of GABA that leads to muscle cells becoming overstimulated.

Between 60% and 80% of people with SPS have antibodies against GAD. These antibodies are also found in other autoimmune conditions, particularly diabetes. This is thought to be why SPS often occurs alongside them.

People with SPS also may have antibodies against another protein called amphiphysin, which is involved in the transmission of signals between nerves. Having these antibodies also increases the risk of breast, lung, and colon cancer.

Diagnosis

A diagnosis of SPS is usually based on a person's symptoms, history, and a physical exam. However, because SPS is a rare disorder, it may be misdiagnosed as multiple sclerosis, fibromyalgia, or a psychological disorder.

Certain tests may also be done to confirm the diagnosis and rule out other conditions. These may include:

• Blood tests and/or lumbar puncture (spinal tap) to look for antibodies against GAD and amphiphysin
• Electromyography (EMG), a test that measures electrical activity in muscle cells
• Magnetic resonance imaging (MRI) of the brain and spine
• Tests to check for other autoimmune diseases, such as hemoglobin A1C for diabetes or thyroid-stimulating hormone (TSH) for thyroiditis

Treatment

Although there is no cure for SPS, treatments can help control symptoms and slow the progression of the disease.

Several different types of medications may be used to reduce pain and control stiffness and spasms, including muscle relaxers, benzodiazepines, and anticonvulsants. Drugs such as Azasan (azathioprine), Valium (diazepam), Neurontin (gabapentin), Gabitril (tiagabine), or Lioresal (baclofen) may be used.

Plasma exchange (plasmapheresis) helps reduce symptoms in some individuals, but this treatment is typically reserved for those with life-threatening respiratory decline. For others, intravenous immunoglobulin (IVIg) is helpful. Both of these treatments aim to slow the immune system's attack on nerve cells.

Physical therapy may help relieve symptoms related to prolonged muscle tension, but it may also trigger muscle spasms. Corticosteroids may help as well, though they must be carefully given to those with diabetes.

Summary

Stiff person syndrome (SPS) is a condition that leads to slowly worsening muscle stiffness and severe muscle spasms that, without treatment, eventually can become disabling. It's thought to be an autoimmune disorder in which antibodies attack cells that help regulate nerve signals that control muscle movement.

The condition is usually diagnosed based on a person's symptoms and tests looking for these antibodies. There is no cure for SPS, but medications and physical therapy can help with stiffness and spasms. For some people, treatments that slow immune system activity may also be used.