Stiff person syndrome, or SPS, is a rare progressive neurological disorder that causes painful muscle spasms, muscle stiffness, and other severe symptoms whose severity varies from person to person. It is primarily an autoimmune condition, meaning it occurs due to the improper functioning of the body’s immune system. Interestingly, stiff person syndrome was initially known as stiff man syndrome but was later renamed, as the disease can affect anyone irrespective of gender or age.

Types of stiff person syndrome
The condition can manifest in many ways. Its main classifications or types include:

• Classic stiff person syndrome
  Classic SPS occurs when the body produces specific antibodies that affect the functioning of an enzyme called glutamic acid decarboxylase (GAD). Up to 80% of people with the condition have this variant, making it the most common.
• Progressive encephalomyelitis with rigidity and myoclonus (PERM)
  This is a more severe type characterized by eye movement issues, decreased consciousness, autonomic dysfunction, and ataxia. It is also known as jerking stiff person syndrome. The condition requires treatment in a hospital due to the occurrence of dysautonomia. Like classic SPS, PERM can be caused due to GAD-related antibodies.
• Focal stiff person syndrome
  As the name implies, this type usually impacts only one limb.
• Paraneoplastic-related stiff person syndrome
  This variant generally affects the nervous system of individuals with cancers like colon cancer, lung cancer, breast cancer, and Hodgkin and non-Hodgkin lymphomas. It is believed to be caused by an antibody different from classic SPS.

Causes of stiff person syndrome
While scientists do not fully understand what causes the condition, research has shown it sets in when an autoimmune response affects the spinal cord and the brain.

Some studies show that patients with stiff person syndrome produce antibodies that work against the GAD enzyme. This enzyme helps make gamma-aminobutyric acid (GABA), a neurotransmitter that controls muscle movement. Research also shows that those with the disease produce antibodies that work against dipeptidyl peptidase-like protein 6 (DPPX), amphiphysin, and glycine receptors. However, there have been instances where patients have not had any known or detectable antibodies.

Risk factors of stiff person syndrome
Individuals with other autoimmune conditions like thyroiditis, pernicious anemia, vitiligo, and type 1 diabetes are more likely to develop this disease. As per the statistics, stiff person syndrome impacts almost double the female population compared to the male population.

Symptoms associated with stiff person syndrome
The signs of the condition include the following:

• Muscle rigidity or stiffness
  In most cases, the torso area (including the back, chest, and abdomen) is the first to get affected by rigidity. The other body parts that might get affected are the hands and legs. Rigidity and stiffness can also develop in other parts and worsen without a clear cause.
• Painful muscle spasms
  Muscle spasms can vary in duration and spread throughout the body or be confined to a specific part. They can be triggered by external stimuli, such as loud noises, unexpected events, physical touch, temperature fluctuations, and stressful situations.
• Agoraphobia and anxiety
  The uncertainty of developing spasms causes patients to become anxious. Some have agoraphobia, where they fear venturing into open or crowded places or leaving their homes.
• Poor posture
  The patient might develop a hunch, making it hard for them to move or walk.

Diagnosis of stiff person syndrome
The condition can be difficult to diagnose as its symptoms closely resemble those of other autoimmune conditions like multiple sclerosis and ankylosing spondylitis. The signs can also be confused for fibromyalgia, anxiety, Parkinson’s disease, and psychosomatic illnesses.

Healthcare professionals identify stiff person syndrome by analyzing the distinct signs, performing neurological and physical tests, and inquiring about the patient’s past health records. Some examinations that can help diagnose the condition are:

• Antibody blood test
  This test looks for the presence and level of GAD antibodies in the patient. While these antibodies are also seen in those with diabetes, their values are ten times higher in stiff person syndrome.
• Electromyography (EMG)
  This test measures the electrical activity in the patient’s muscles. It can help eliminate other possible causes of one’s symptoms.
• Lumbar puncture (spinal tap)
  To check for GAD antibodies, healthcare professionals extract a tiny amount of fluid from the patient’s spinal canal. This helps them confirm the diagnosis and receive clues about other possible underlying conditions.

Treatment of stiff person syndrome
While the condition has no cure, the right treatment and care can help control the symptoms and improve the patient’s quality of life. Healthcare professionals recommend remedies that relieve rigidity, stiffness, and painful muscle spasms. Massage therapy, physical therapy, heat therapy, hydrotherapy, acupuncture, and stem cell transplant are a few treatments that help patients.

Some studies reveal that intravenous immunoglobulin (IVIG) treatment can help improve the symptoms of this condition. It involves collecting antibodies from the plasma of healthy donors and infusing them into the patient’s bloodstream.