Stiff person syndrome (SPS) is a rare autoimmune neurological disorder that involves muscle spasms and rigidity. People with SPS may experience heightened sensitivity to touch, noise, emotional distress, and other stimuli, which can trigger symptoms.

This article looks at what SPS is in more detail, including the symptoms, causes, who gets SPS, and diagnosis. We also look at treatments, living with SPS, related conditions, and the outlook for the condition.

A healthcare professional treating a patient in a hospital bed, who may have stiff person syndrome.Share on Pinterest
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SPS is a rare neurological disease with the characteristics of an autoimmune disease. People with the condition experience recurring muscle rigidity in their limbs and torso and muscle spasms that occur spontaneously or due to heightened sensitivity to stimuli.

Loud noises, such as car horns or other stimuli, can trigger spasms and falls, which can leave people with the condition fearful of going about their everyday activities.

The symptoms of SPS often progress slowly and can lead to disability. In some cases, SPS can be fatal. Some people with the condition may also have other autoimmune disorders, such as:

A diagram explaining the symptoms of stiff person syndrome (SPS).Share on Pinterest
A diagram explaining the symptoms of stiff person syndrome (SPS). Infographic by Diego Sabogal.

People typically develop symptoms of SPS between the ages of 20 and 60 years, and the condition usually affects people during their 30s and 40s.

Symptoms of SPS include:

  • stiffness and rigidity in the trunk muscles
  • difficulty turning and bending
  • rigidity in the upper and lower limbs
  • an atypical hunched posture
  • stiff gait and difficulty walking
  • painful muscle spasms
  • falls
  • exaggerated startle responses to stimuli such as noise or emotions

People with SPS often develop mental symptoms due to anticipating spasms from stimuli and social and physical limitations. These include:

In the later stages of SPS, the condition can affect the facial muscles. Some people may also experience severe, long lasting spasms that require intravenous muscle relaxants. In rare cases, the condition can affect the respiratory muscles.

In people with autoimmune disorders, the immune system mistakenly attacks healthy cells and tissues in the body as if they were harmful antigens.

In 80% of cases of SPS, people produce a type of antibody called glutamic acid decarboxylase (anti-GAD). This attacks proteins in the brain neurons that affect muscle movement, affecting spinal cord and brain function.

Experts do not know exactly why autoimmune diseases occur, although genetics likely play a role.

SPS is rare — about one to two individuals per million have the condition.

Females are twice as likely as males to develop SPS, and people generally experience symptoms in their 30s and 40s.

People with other autoimmune conditions may be at higher risk of SPS. These include:

  • vitiligo
  • diabetes
  • thyroiditis
  • pernicious anemia
  • celiac disease

To diagnose SPS, a healthcare professional may use the following diagnostic tools:

  • A physical exam: The doctor will also ask a person about their symptoms.
  • A blood test to look for GAD antibodies: Most people with SPS have these antibodies.
  • An electromyography (EMG): This measures and assesses the electrical activity in the muscles.
  • An MRI scan: Helps rule out other causes of spasms and muscle rigidity and check for other autoimmune conditions.

There is no cure for SPS, but treatments can help control the symptoms.

A healthcare professional may prescribe calming, anticonvulsant, and muscle-relaxing medications, such as:

Doctors may also prescribe antidepressant and anti-epileptic medications to treat psychiatric symptoms and seizures that may co-exist with SPS.

An individual with SPS may also benefit from disease-modifying therapies. This treatment aims to change the immune response and reduce or remove the harmful antibodies that are attacking healthy cells. For SPS, this typically involves intravenous immunoglobulin (IVIG), which may promote improvement in symptoms for up to 1 year after a course of five sessions.

Although further research is necessary to determine their efficacy, some people with SPS have reported improvement after using the following medications:

In addition to medication, a person may benefit from physical therapy. This may help improve muscle tone, posture, and range of motion.

People with SPS often develop mental and emotional symptoms alongside physical symptoms, which can greatly affect their quality of life.

A person should seek support and treatment for anxiety, depression, and fear of the outside world. This typically consists of:

In classic SPS, which presents in 70–80% of individuals with the condition, individuals may also have co-existing autoimmune conditions such as:

  • diabetes
  • pernicious anemia
  • vitiligo
  • thyroiditis
  • celiac disease

Researchers have linked the less common paraneoplastic variant of SPS to various cancers, including:

Healthcare professionals can treat SPS with various medications. However, these treatments are not a cure and will only help relieve the symptoms and severity of the condition. That said, doctors can help a person control the symptoms well in most cases.

People with SPS may experience frequent falls as they do not have highly functioning defensive reflexes that typically act in these situations. Because of this, they may experience injuries that can sometimes be serious.

Despite treatment, some people with SPS experience disability, inability to walk, and orthopedic problems due to the condition’s progression over time. Many people with SPS may also experience a reduced quality of life due to limitations in their physical and social activities.

Here are some answers to common questions about SPS.

Is stiff person syndrome fatal?

Doctors can treat the symptoms of SPS effectively. However, without treatment, the condition can be fatal.

Is stiff person syndrome progressive?

Yes, SPS is progressive. Stiffness may become more widespread in the body and more severe over time.

SPS is a rare autoimmune neurological disorder where a person’s muscles spasm and become rigid. This can occur spontaneously or due to an exaggerated startle response to noises, emotional distress, and other stimuli.

People with SPS often develop mental and emotional symptoms, such as depression and anxiety. This is because they may worry about experiencing spasms and falls and become fearful of the outside world. They may also experience a reduced quality of life due to physical and social limitations.

Treatment for SPS comprises various anticonvulsants, muscle relaxants, antianxiety medications, pain relievers, IVIG, and antidepressants. Despite treatment, some people may experience disability, an inability to walk, and orthopedic problems as the disorder progresses.