What Is Stiff Person Syndrome?

Stiff person syndrome (SPS) is a rare neurological disorder that causes muscle stiffness and repeated muscle spasms triggered by light touch, sudden noise, emotional distress, or exposure to cold temperatures. SPS is a progressive disease and may lead to posture changes, difficulty walking, and challenges performing everyday tasks. 

SPS is extremely rare, affecting fewer than 5,000 people in the United States. Researchers don't know exactly what causes SPS, though evidence suggests it may occur due to an abnormal autoimmune response in the central nervous system (brain and spinal cord). There is no cure for SPS, but treatment can help manage symptoms and improve the quality of life of people living with this challenging condition.

Types of SPS

There is no universally agreed-upon classification system, but experts typically differentiate types of stiff person syndrome (SPS) based on which body parts are affected and whether there are additional neurological symptoms. Types of SPS include:

• Classic SPS: This is the most common form, affecting about 70% of people with SPS. Symptoms typically develop gradually, including muscle stiffness and spasms primarily affecting the torso and legs.
• Partial SPS: Also known as focal SPS, this type involves muscle stiffness and spasms limited to one area, such as one leg (stiff leg syndrome) or the torso (stiff torso syndrome). In some cases, partial SPS can progress to classic SPS.
• SPS-plus: This type includes the classic SPS symptoms (e.g., stiffness and spasms in the back and limbs) alongside neurological problems like double vision, vertigo, reduced coordination, and speech or swallowing problems.
• Progressive encephalomyelitis with rigidity and myoclonus (PERM): This is a more severe form of SPS that causes rapid onset of symptoms that progress quickly. Along with muscle stiffness and spasms, people with PERM experience additional symptoms such as vertigo, trouble speaking, confusion, seizures, and involuntary muscle jerks (myoclonus).

Stiff Person Syndrome Symptoms 

Symptoms of stiff person syndrome typically develop gradually and slowly worsen over months or years. Most people with SPS develop symptoms between the ages of 30 to 60.

Muscle Stiffness 

The hallmark symptom of SPS is progressive, fluctuating muscle stiffness in the torso (abdomen, back, and chest) and limbs (arms and legs). Pain or discomfort may initially affect the lower back, hips, and/or legs, and your muscles may feel tight and achy. Over time, stiffness can affect other muscles in the body, such as the arms, neck, and shoulders. 

As the disease progresses, muscle stiffness may cause difficulty walking, and many people with SPS develop a hunched posture due to the lower spine curving inward (hyperlordosis). These changes increase the risk of falls; some people may require a wheelchair or other mobility device.

Muscle Spasms 

People with SPS can experience sudden and severe muscle spasms triggered by factors such as:

• Unexpected or loud noises 
• Light touch
• Cold temperatures
• Emotional distress 
• Stress
  

Muscle spasms can be excruciating and may affect a specific muscle (e.g., back muscle) or the entire body. Spasms can last from several minutes to hours and are most common during waking hours. Depending on the muscle(s) affected, spasms can lead to:

• Falls and injuries, especially leg muscle spasms 
• Feeling bloated or a sensation of tightness when abdominal muscles are involved 
• Difficulty breathing or shortness of breath when chest and respiratory muscles are involved 

Anxiety and Depression

Nearly half of those with stiff person syndrome experience a mental health condition, such as anxiety and depression. Due to the unpredictable nature of environmental noises and other triggers (e.g., temperature changes, unexpected touch), some people with SPS experience intense anxiety when they need to leave home and develop a fear of going outside unassisted (agoraphobia).

The progressive nature of SPS can be incredibly difficult to live with and trigger or worsen anxiety and depression. Chronic pain and feelings of uncertainty can contribute to constant muscle stiffness and unpredictable muscle spasms.

Evidence also suggests that SPS may disrupt the brain's chemical messaging system and reduce gamma-aminobutyric acid (GABA) levels. GABA is a neurotransmitter (chemical messenger) that helps calm the nervous system, helping your nerves process sensory input. Low GABA levels are associated with an increased risk of mental health disorders. Early research has hypothesized that low GABA activity may play a role in why so many people with SPS experience anxiety and depression.

Hyperhidrosis 

Hyperhidrosis, or excessive sweating, is a common symptom of stiff person syndrome. Dysregulation of the autonomic nervous system that controls functions like sweating and heart rate may contribute to excessive sweating in some people with SPS. Anxiety may also trigger sweating episodes.

What Causes Stiff Person Syndrome? 

Researchers are working to determine exactly what causes stiff person syndrome. Evidence suggests it is an autoimmune disorder that develops when the immune system mistakenly attacks glutamic acid decarboxylase (GAD). This enzyme triggers the production of neurotransmitter gamma-aminobutyric acid (GABA). GABA calms neurons responsible for muscle movement and helps prevent excess muscle activity.

In people with SPS, the immune system produces antibodies that attack GAD, leading to decreased production of GABA. Low levels of GABA causes the neurons responsible for muscle movement to continuously send signals to the brain, leading to uncontrolled muscle stiffness and spasms. 

Risk Factors

While the exact trigger for the body's abnormal autoimmune reaction is unclear, certain factors are associated with an increased risk of developing SPS.

• Sex: People assigned female at birth are twice as likely to develop SPS than people assigned male at birth. 
• Age: SPS can affect people of all ages, but most commonly develops between the ages of 30 to 60.
• Underlying autoimmune diseases: People with other autoimmune conditions have a higher risk of developing SPS, especially those with type 1 diabetes, vitiligo, thyroiditis, and pernicious anemia. 

Diagnosis

Diagnosing stiff person syndrome can be challenging due to its rarity and the overlap of its symptoms with other conditions, such as fibromyalgia and multiple sclerosis.

Healthcare providers (like a neurologist, or a doctor specializing in the brain and nervous system) begin the diagnostic process by reviewing your medical history and performing a physical examination. Diagnostic tests are necessary to rule out other possible causes of your symptoms and confirm a diagnosis. These tests may include:

• Blood tests: Check for the presence and amount of antibodies against glutamic acid decarboxylase (GAD) in the blood. 
• Spinal tap (lumbar puncture): Involves collecting and analyzing a small amount of cerebrospinal fluid, the fluid surrounding the brain and spinal cord, for the presence of GAD antibodies.
• Electromyography (EMG): Measures and records electrical activity in muscles at rest and during muscle contractions, helping assess muscle function and identify abnormal muscle activity patterns associated with SPS.
• Imaging tests: Healthcare providers may order imaging tests, such as magnetic resonance imaging (MRI), computed tomography scan (CT), or positron emission tomography scan (PET), to rule out other possible causes of symptoms, such as spinal stenosis or cancer. 

Treatments for SPS

There is no cure for stiff person syndrome, so treatment focuses on reducing muscle spasms and stiffness and suppressing the overactive immune response to maintain mobility and physical function. Treatment approaches vary, depending on the type and severity of your symptoms.

Medications

Medications are the primary treatment for stiff person syndrome. Depending on your symptoms, your healthcare provider may prescribe:

• Muscle relaxants: Muscle relaxers help reduce muscle tension and stiffness and relieve muscle spasms. Some also reduce anxiety. Diazepam (benzodiazepine) is the most common muscle relaxant for treating SPS. Your healthcare provider may prescribe oral medications or administer your medication intravenously (IV) directly into a vein on your arm. 
• Anticonvulsants: Certain medications for treating seizures, such as gabapentin and vigabatrin, are similar to the neurotransmitter GABA. These help to manage nerve activity and reduce muscle spasms and stiffness.
• Botulinum toxin injections: Botulinum toxin injections, more commonly called Botox, can temporarily relieve muscle spasms. Healthcare providers may use these injections in people with local SPS (e.g., affecting one leg) to provide short-term relief.  
  

Immunotherapy 

When other treatments are ineffective, healthcare providers may prescribe immunotherapy to treat SPS. These drugs help regulate the immune system by suppressing the overactive immune response by decreasing the production of antibodies that lead to SPS symptoms.

• Intravenous immunoglobulin (IVIg): Monthly immunoglobulin infusions can improve muscle stiffness and flexibility, reduce hyperexcitability (sensitivity to sounds and touch), and improve physical function in people with SPS. 
• Rituxan (rituximab): In a class of medications called monoclonal antibodies, Rituxan (rituximab) injections may help control SPS symptoms in people who do not respond to other medicines. Some people may need repeat injections every 3-6 months or every 6 to 12 months to manage symptoms. 

Physical Therapy

Physical therapy can help people with SPS manage symptoms and improve or maintain their mobility. Physical therapists develop personalized treatment programs that may include:

• Stretching and gentle exercises maintain muscle flexibility and allow people with SPS to retain the ability to perform everyday tasks. 
• Range of motion exercises to improve balance, coordination, and overall physical function to prevent falls and maintain safe mobility.
• Pain management therapies like hydrotherapy, massage, and relaxation exercises.

Prevention

Unfortunately, there is currently no guaranteed way to prevent stiff person syndrome. Factors that cause muscle spasms, such as unexpected or loud noises and light touch, are common everyday occurrences, which makes it challenging to avoid possible triggers. 

Following your treatment plan and regular check-ups with your healthcare provider are the best ways to manage the condition and control symptoms. Some evidence suggests that a gluten-free diet may help manage symptoms in people with SPS, though more research is needed to determine the impact a gluten-free diet has on symptom management.

Related Conditions 

Many people with stiff person syndrome also have other underlying, related conditions. 

Autoimmune Disorders

Up to 80% of people with SPS have another autoimmune disorder, particularly conditions related to the endocrine system (made up of soft tissues and glands that release hormones). Type 1 diabetes, thyroid disease, and pernicious anemia are prevalent in people with SPS, and researchers are currently investigating the connections between the disorders.

Cancer

People with SPS have an increased risk of certain types of cancer, including breast cancer, lung cancer, and lymphoma. Research is ongoing to understand the link between SPS and certain types of cancer.

Living With Stiff Person Syndrome

Stiff person syndrome is a rare but severe condition that can significantly impact your daily routine and quality of life. Living with SPS often means making lifestyle changes to manage the challenges the painful, sometimes debilitating symptoms can cause. This might include: 

• Using assistive devices: Canes, walkers, and wheelchairs can help you maintain mobility and independence.
• Modifying your home environment: Updating your living space can help you stay safe, such as installing grab rails, handrails, or ramps. This can lower your risk of falls and related injuries.
• Seeking emotional support: Talking to your healthcare provider and/or a counselor can help manage the emotional impact of SPS. Joining a support group for people with SPS can be an excellent way to connect with others who understand what you're going through.

Living with a chronic condition like stiff person syndrome requires following your treatment plan and regular visits with your healthcare provider for monitoring and treatment changes as needed.