What to Know About Stiff Person Syndrome

Medically Reviewed by Jabeen Begum, MD on October 13, 2022
4 min read

Stiff person syndrome (also known as SPS, Moersch-Woltman syndrome, and stiff man syndrome) is a very rare condition that can cause your muscles to become rigid or spasm. This is a progressive neurological and autoimmune disorder that affects the brain and the spinal cord. 

Here’s what else you need to know about stiff person syndrome, including causes, symptoms, and treatment. 

Stiff person syndrome is so rare that in the U.S., fewer than 5,000 living people have been diagnosed with it. It’s a progressive autoimmune disorder that affects the central nervous system, mostly the brain and spinal cord.

People with SPS initially experience rigidity in the muscles of their trunk, which can then spread to other parts of the body over time. Besides stiff muscles, stiff person syndrome can also cause intense muscle spasms. The stiffening can cause a change in posture over time, so people with SPS commonly hunch over.

The muscle spasms can occur at random or be triggered by something, typically a noise, physical touch, or feelings of emotional distress. Bouts of spasms can affect just one area, or they can spread throughout the entire body.

People with stiff person syndrome frequently experience painful muscle spasms that can carry on for hours. Sometimes, these muscle spasms can be so strong that they can fracture your bones. They continue until the stimulus that provoked them is gone and your muscles can begin to slowly relax.

Another primary symptom of SPS is muscle stiffening that begins in the torso and then gradually works its way down your limbs. The muscles usually also become enlarged. At first, the muscle stiffness may come and go, but over time, it becomes constant.

Because of these symptoms, people with SPS might find it hard to walk or move. The stiffness can cause you to fall when standing or walking, and this falling down has been described as “log-like” since you become very rigid and can’t stop yourself or break the fall.

It’s not uncommon for people with SPS to develop symptoms of anxiety and depression, too. You might become afraid to leave the house since the muscle spasms and stiffness are so unpredictable. People worry they will experience a bout of spasms or stiffness in public. People with SPS are also more sensitive to noise and sudden movements, as these can be triggers.

Doctors haven’t yet pinpointed an exact cause of stiff person syndrome. They do know, though, that most people with SPS have antibodies that target an enzyme called glutamic acid decarboxylase (GAD), which is involved in creating the inhibitory transmitter GABA, which in turn helps to control muscle movement. This autoimmune attack on the GAD enzymes is thought to trigger an autoimmune response.

Doctors have also noticed that people with SPS usually have other autoimmune disorders, such as:

Stiff person syndrome is also more likely to develop if you have certain kinds of cancers, including cancer of the:

  • Lungs
  • Kidneys
  • Breasts
  • Thyroid
  • Colon

Symptoms of stiff person syndrome typically manifest between the ages of 30 and 60. Women are twice as likely to be diagnosed. 

Because of its symptoms, SPS is often misdiagnosed as:

  • Multiple sclerosis
  • Parkinson’s disease
  • Fibromyalgia
  • Psychosomatic illness
  • Muscular dystrophy
  • Anxiety
  • Phobia

To obtain a diagnosis, your doctor will perform a physical examination and ask you about your medical history. They may order several tests to rule out other conditions. The first test is usually a blood test to check for GAD antibodies since between 60% and 80% of people with SPS will display elevated levels.

Your doctor can also employ electromyography (EMG), recording the electrical activity of your muscles when they are at rest and when they contract. The purpose of this test is to check for continuous activity in the muscles.

Current treatment for stiff person syndrome focuses on relieving symptoms to facilitate the normal performance of daily activities. There currently isn’t a cure for SPS, so treatment plans are tailored to manage your personal symptoms.

Your doctor may try different medication options to manage your pain and control the muscle spasms. It may take some time to find the right combination of medications, though, since not everyone’s body responds the same way. Benzodiazepines, like diazepam and clonazepam, or baclofen are common medications that are used to treat muscle stiffness and spasms, and anti-inflammatories or anti-seizure medications can help manage pain. While more research is needed, studies indicate that intravenous immunoglobulin may also be a way to effectively treat stiff person syndrome.

Besides medication, activities like stretching can help keep your muscles active and loose. Some people opt for additional treatments like physical therapy (including heat or aqua therapy), massages, or acupuncture to relieve pain.

Even though there is no cure for this condition, many people with stiff person syndrome are still able to manage their symptoms with the right treatment plan, helping them to live as normal of a life as possible.