What Is Stiff Person Syndrome (SPS)?

Stiff person syndrome (SPS) is a rare autoimmune neurological disorder that causes severe and painful muscle spasms that come and go and usually worsens over time. Some people with SPS also have gait issues, vision problems, and speech problems. Symptoms depend on which type of SPS a person has.

There is no cure for SPS. Treatments are used to help manage symptoms and reduce the muscle spasms that occur with SPS. Typical treatments include medications and specialists such as physical therapists, occupational therapist, and speech therapists. The condition is extremely rare, affecting 1 or 2 people out of every million people in the general population. Since stiff person syndrome is a spectrum disorder, ranging in levels of severity, it is suspected that it is underdiagnosed. SPS typically develops between the ages of 30 and 50 and is more common in females than males. In rare occasions, younger people, even children, may develop the disorder.

SPS is often associated with other autoimmune disorders, which include:

• Type 1 diabetes
• Autoimmune thyroid disease
• Pernicious anemia
• Celiac disease
• Vitiligo 

There are several different types of stiff person syndrome. SPS types include:

• Classic SPS. This is the most common form of SPS. Research has shown that GAD (glutamic acid decarboxylase) antibodies are strongly associated with classic SPS, although other antibodies may also be involved.
• SPS variants. Variants for SPS involve specific parts of the body or involve problems with coordination of muscles (ataxia).
• Progressive encephalomyelitis with rigidity and myoclonus (PERM). This is the most severe type of SPS. The condition can cause autonomic dysfunction, decreased consciousness, eye movement problems, and coordination issues (ataxia). Some people with this type of SPS are constantly hospitalized due to autonomic dysfunction. 

Signs and Symptoms

Symptoms for SPS vary among individuals. Symptoms can come and go and have varying degrees of severity. Typically, muscle spasms related to SPS begin in the legs and back, but sometimes can affect the abdomen, and in rare cases, can affect the upper trunk, arms, and face. Symptoms may take several months to a few years to develop and tend to get worse over time. The spasms can significantly impact daily functioning and limit people from daily life activities.

Muscle spasms with SPS can be triggered by unexpected loud noises, stress, physical touch or stimulation, or changes in temperature (especially changing to colder temperatures. The muscle spasms tend to be extremely rigid and board-like.

The most common symptoms of SPS include:

• Stiff muscles or muscle rigidity
• Painful muscle spasms or contractions
• Difficulty walking
• Stiff or rigid posture
• Gait or balance issues due to muscle spasms
• Shortness of breath if the chest muscles are impacted
• Chronic pain
• Hyperlordosis (an exaggerated curve in the lower back that can lead to spinal compression)
• Anxiety and agoraphobia due to falls caused by muscle spasms
• Eye movement issues and double vision
• Coordination issues
• Speech issues

Causes

The exact cause of stiff person syndrome is unknown, but as in all autoimmune disorders, symptoms arise when the immune system mistakenly sends antibodies to attack healthy cells and tissue. Specifically, SPS develops when the immune system attacks a protein known as glutamic acid decarboxylase (GAD). GAD helps to make a neurotransmitter called gamma-aminobutyric acid (GABA), which aids in the regulation of motor neurons by decreasing their activity. Motor neurons control muscle movements. In people with SPS, low levels of GABA can cause the motor neurons to fire continuously when they are not supposed to.

However, not all people with GAD antibodies have adverse side effects or develop SPS. SPS is often associated with other autoimmune disorders, which include:

• Type 1 diabetes
• Autoimmune thyroid disease
• Pernicious anemia
• Celiac disease
• Vitiligo 

Additionally, SPS is also more common in people with certain types of cancer (breast cancer, lung cancer, kidney cancer, thyroid cancer, colon cancer, and lymphomas). This is referred to as paraneoplastic SPS.

Risk Factors

There are several conditions that put people at a greater risk of developing SPS. Those conditions include:

• Type 1 diabetes
• Autoimmune thyroid disease
• Pernicious anemia
• Celiac disease
• Vitiligo
• Cancer (breast cancer, lung cancer, kidney cancer, thyroid cancer, colon cancer, and lymphomas) 

Diagnosis

Determining a diagnosis of SPS can be a difficult task. Your doctor will evaluate your symptoms, take a thorough medical history, and conduct a physical examination. There are also several test doctors may administer if SPS is suspected. Tests include:

• Blood tests. These tests look for abnormalities in the blood, specifically if the anti-GAD65 antibody is present. This antibody is present in about 80% of the people diagnosed with SPS. High levels of this antibody would be indicative of SPS. Blood tests can also assess for other autoimmune related disorders, other antibodies, and vitamin deficiencies.
• Electromyography (EMG). This test evaluates the body’s nerve and muscle functioning. Signs of SPS may show up on an EMG.
• Imaging tests. Imaging tests, such as MRI’s, CT scans, PET scan, or an FDG-PET scan, are typically used to rule out other conditions. These tests allow doctors to view images of the brain, spinal cord, and nerves.
• Lumbar puncture (spinal tap). This procedure can detect the anti-GAD65 antibody and it can also be used to rule out other conditions. 

Treatment

Currently, there is no cure for stiff person syndrome. Treatment for SPS will be dependent on the type of SPS and it will be tailored to help manage your specific set of symptoms. SPS is a complex issue and treatment will address the autoimmune, neurologic, pain, mobility, and visual aspects of the syndrome. Appropriate treatment can help to reduce symptoms of SPS and increase a person’s quality of life. The most common forms of treatment include:

• Medications and therapies for symptom management
• Immunotherapy 

Additionally, your healthcare provider may refer you to a team of specialists, depending on your specific symptoms. Specialists may include:

• Neurologists or neuroimmunologists
• Occupational and physical therapists
• Physical medicine and rehabilitation specialists
• Speech therapist
• Mental healthcare providers 

Medications and therapies for symptoms

• Benzodiazepines. This class of medication is known to affect GABA signals. It is often used to treat anxiety, insomnia, and seizures. Doctors typically use this as the first line of defense for SPS.
• Muscle relaxants. This type of medication helps to relax the muscles and reduce muscle stiffness and rigidity.
• Neuropathic pain medications. These types of medications, such as gabapentin and pregabalin, also impact GABA signals and can help to reduce symptoms of SPS. 

Other therapies that may help to manage symptoms include:

• Massage
• Physical therapy
• Hydrotherapy
• Heat therapy
• Acupuncture 

Immunotherapy

Research has indicated that intravenous immunoglobulin (IVIg) treatment may help to reduce symptoms of people with SPS. Immunoglobulins are natural antibodies your body produces. An intravenous immunoglobulin (IVIg) uses immunoglobulins donated by people with healthy immune systems. Other immunotherapies include:

• Plasma exchange
• Intravenous immunosuppressant therapy
• Oral immunosuppressant therapy 

Prevention

There is no known way to prevent the development of SPS.

Complications

Complications that can occur from SPS include blood clots or wound infection due to immobility. In rare cases, spasms of the chest muscle may cause difficulty with breathing.