What Is Stiff-Person Syndrome (SPS)?

Stiff-person syndrome is a neurological disorder that is characterized by muscle stiffness and painful muscle spasms.

It is a rare condition that only affects one or two persons in every million people. It is estimated that fewer than 5,000 people in the United States live with this condition.

This article explores the types, causes, symptoms, and diagnosis of stiff-person syndrome, as well as some treatment options and coping strategies that may be helpful.

Symptoms of Stiff-Person Syndrome 

The main symptoms of stiff-person syndrome are muscle stiffness and muscle spasms.

Muscle Stiffness

The muscles in the torso (chest, back, and abdomen) and sometimes the limbs (arms and legs) become stiff and rigid, which can be painful and uncomfortable.

The stiffness may spread to other areas of the body and either fluctuate in intensity or get progressively worse. Over time, the person may develop a hunched posture, which can make it hard for them to walk and perform other everyday activities.

Muscle Spasms

Muscle stiffness is often alternated with episodes of painful muscle spasms. The muscle spasms typically last a few seconds or minutes, but can sometimes last for a few hours. They may affect specific parts of the body or the entire body. The spasms may be so severe in intensity that they can cause the person to fall down.

The muscle spasms may be triggered by:

• Light
• Loud or unexpected noises
• Sudden movements
• Temperature changes
• Emotional stress
• Physical touch or stimulation
  

Types of Stiff-Person Syndrome 

The different types of stiff-person syndrome include:

• Classic stiff-person syndrome
• Focal stiff-person syndrome
• Jerking stiff-person syndrome
• Progressive encephalomyelitis with rigidity and myoclonus (PERM)
• Paraneoplastic-related stiff-person syndrome

Causes of Stiff-Person Syndrome 

While the exact causes of stiff-person syndrome are unknown, research indicates that it is caused by a faulty autoimmune response in the brain and spinal cord. It is therefore classified as an autoimmune disorder. Autoimmune disorders are a group of conditions wherein the person’s immune system mistakenly attacks and harms their healthy cells.

While there are different types of autoimmune disorders, stiff-person syndrome is a type of autoimmune disorder that causes the muscles to fail to work the way they should. This is challenging because we rely on the strength and support of our muscles for every action we do, including walking, sitting, standing, and typing. 

In people with stiff-person syndrome, their immune system attacks a protein in the body known as glutamic acid decarboxylase (GAD), by creating GAD antibodies. GAD is an enzyme that is required to make a neurotransmitter known as gamma-aminobutyric acid (GABA), which helps control muscle movement by decreasing the activity of motor neurons. Low levels of the GABA neurotransmitter can cause motor neurons to fire excessively, even when they’re not supposed to.

However, the association between GAD antibodies and stiff-person syndrome is still being researched, because some people with GAD antibodies don’t have stiff-person syndrome and some people with stiff-person syndrome don’t have any unusual antibodies. Approximately 60% to 80% of people with stiff-person syndrome have GAD antibodies in their blood and spinal fluid.

These are some of the risk factors that can make a person more likely to develop stiff-person syndrome:

• Gender: Stiff-person syndrome affects twice as many women and people assigned female at birth than men and people assigned male at birth.
• Age: The symptoms of stiff-person syndrome tend to appear between the ages of 30 and 40.
• Autoimmune conditions: Stiff-person syndrome is often associated with the presence of other auto-immune conditions such as celiac disease, vitiligo, pernicious anemia, autoimmune thyroid disease, and type 1 diabetes.
• Cancer: Stiff-person syndrome is more prevalent in people who have certain forms of cancer, such as lung cancer, breast cancer, colon cancer, thyroid cancer, kidney cancer, and lymphomas.

Diagnosing Stiff-Person Syndrome 

Stiff-person syndrome can be difficult to diagnose because it is a rare condition and its symptoms are often mistaken for those of other conditions such as multiple sclerosis, fibromyalgia, or Parkinson’s disease. The diagnostic process may therefore involve several tests to confirm the symptoms and rule out other health conditions.

The diagnostic process may include the following tests:

• Antibody blood test: A blood test can check for the presence of GAD antibodies as well as unusual levels of other antibodies in the blood.
• Electromyography (EMG): An electromyography test detects the electrical activity levels in the muscles, in order to rule out other health conditions.
• Lumbar puncture: Also known as a spinal tap, a lumbar puncture test involves using a needle to draw fluid from the spinal canal. The fluid is then tested for GAD antibodies.

Treating Stiff-Person Syndrome 

Treatment for stiff-person syndrome may involve medical and non-medical interventions.

Non-Medical Interventions 

There are several therapies that help relax the muscles and relieve pain, such as:

• Stretching
• Aqua therapy
• Heat therapy
• Massage
• Acupuncture
• Speech therapy
• Occupational therapy
• Physical therapy

Medications 

The symptoms of stiff-person syndrome can be managed with medications such as:

• GABA-ergic agonist drugs, known as benzodiazepines, such as diazepam and clonazepam, which can help treat muscle stiffness and muscle spasms. 
• Muscle relaxants, such as baclofen, which may also be prescribed along with benzodiazepines. 
• Anti-seizure drugs, including pregabalin, vigabatrin, valproate, and gabapentin.

Immunomodulating Therapies

Research shows that certain immunomodulating therapies such as plasmapheresis and intravenous immunoglobulin (IVIG) can also help improve the symptoms of stiff-person syndrome.

A Word From Verywell

If you or a loved one have been diagnosed with stiff-person syndrome, you may find it difficult to cope with the symptoms and reality of living with the condition. It can be helpful to visit a mental healthcare provider to process your feelings and develop coping strategies. 

You may also benefit from joining a support group of people living with stiff-person disorder or other autoimmune conditions, as they can be a source of advice, resources, and a shared sense of understanding.