We rely on our muscles all day, every day, to carry our coffee, type on our computers, and walk to the grocery store. But, though it’s rare, those muscles can sometimes rebel against us. Stiff Person Syndrome (SPS) is an autoimmune and neurological disorder that can make the muscles in the torso and limbs alternate between rigidity and spasms.

The cause of this extremely rare disease is still unknown. But researchers suspect that it may be the result of an autoimmune reaction where the body attacks nerve cells in the central nervous system that control muscle movement.

“People with Stiff Person Syndrome can run the spectrum from mild to severe, and a personalized approach to treating the disease is the best way to ensure an improved outcome,” says Richard Nowak, MD, a neurologist at Yale Medicine.  

The main symptoms of Stiff Person Syndrome are muscle stiffening in the torso and limbs, along with episodes of violent muscle spasms. These can be triggered by environmental stimuli (like loud noises) or emotional stress. The muscle spasms can be so severe that they cause the person to fall down. The muscles gradually relax after the stimulus is gone.

These symptoms can lead to difficulty walking and, over time, even greater disability. People with Stiff Person Syndrome are also more likely to have symptoms of depression and anxiety.  In part, this is because of the unpredictability of the disease, but patients also have lower levels of the neurotransmitter GABA, which regulates anxiety.

Most people start experiencing symptoms between the ages of 30 and 60. 

Though the cause of Stiff Person Syndrome remains unknown, researchers suspect it may be caused by an autoimmune reaction. Specifically, the immune system seems to attack a protein called glutamic acid decarboxylase (GAD), which helps make a substance called gamma-aminobutyric acid (GABA). 

GABA helps regulate motor neurons by decreasing their activity. Low levels of GABA can cause those neurons to fire continuously even when they’re not supposed to. About 60-80 percent of Stiff Person Syndrome patients have anti-GAD antibodies in their blood and cerebrospinal fluid (a water-like substance surrounding the brain).

Many patients with SPS also have another autoimmune disease, such as type 1 diabetes, vitiligo, and pernicious anemia. SPS is also more common in people with certain kinds of cancer, including breast cancer, lung cancer, kidney cancer, thyroid cancer, colon cancer, and lymphomas. However, the reason for these links is still unknown. 

Reaching a diagnosis for Stiff Person Syndrome can be difficult. Generally, SPS is suspected based on characteristic symptoms. A comprehensive medical history and examination, along with additional investigations, including blood tests and spinal fluid analysis, can confirm the diagnosis. When conducting those tests, your doctor is looking for elevated levels of GAD antibodies. 

Electromyography or EMG is also sometimes recommended to study the electrical activity of skeletal muscles. Your doctor will be looking for typical motor unit activity findings that are common in people with SPS.

Doctors will also rule out other possible causes of symptoms, including Parkinson’s disease, multiple sclerosis, fibromyalgia, psychosomatic illness, or anxiety and phobia.

There is no cure for Stiff Person Syndrome. When doctors treat patients with this condition, they focus on relieving symptoms with medications such as sedatives, muscle relaxants, and steroids. Intravenous Immunoglobulin and plasmapheresis, among other immunotherapies, may also be prescribed. Physical, occupational, and aqua therapy are also important for patients with SPS. 

At Yale Medicine, we have a team of highly trained physicians who are dedicated to understanding and treating the entire spectrum of nervous system diseases. Our doctors combine knowledge gathered in the lab with the latest technology to treat our patients. Nested within the neurology department is the Yale Medicine Movement Disorders Clinic, which specializes in treating a full range of movement disorders, including Stiff Person Syndrome.