What is SPS

General Discussion

Stiff-person syndrome (SPS) is a rare acquired neurological disorder characterized by progressive muscle stiffness (rigidity) and repeated episodes of painful muscle spasms. Muscular rigidity often fluctuates (i.e., grows worse and then improves) and usually occurs along with muscle spasms. Spasms may occur randomly or be triggered by a variety of different events including a sudden noise or light physical contact. In most cases, other neurological signs or symptoms do not occur. The severity and progression of SPS vary from one person to another. If left untreated, SPS can potentially progress to cause difficulty walking and significantly impact a person's ability to perform routine, daily tasks. Although the exact cause of SPS is unknown, it is believed to be an autoimmune disorder and sometimes occurs along with other autoimmune disorders.​

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Signs & Symptoms

The characteristic findings associated with SPS are progressive, fluctuating muscular rigidity that occurs along with muscle spasms. The severity and progression of SPS can vary from one person to another. The symptoms usually develop over a period of months and may remain stable for many years or slowly worsen. In some people, symptoms can be stabilized through medication. Affected individuals should talk to their physician and medical team about their specific case, associated symptoms and overall prognosis.

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In many cases, SPS begins slowly over several months or a few years. Affected individuals may initially experience aching discomfort, stiffness, or pain, especially in the lower back or legs (predominantly classic type). Early on, stiffness may come and go, but it gradually becomes fixed. The shoulders, neck, and hips may also be affected. As the disease progresses, stiffness of the leg muscles develops, and is often more pronounced on one side than the other (asymmetrical). This leads to a slow, stiff manner of walking. As stiffness increases, affected individuals may develop a hunched or slouched posture due to outward curving of the upper spine (kyphosis) or an arched back due to inward curving of the lower spine (hyperlordosis). In some individuals, stiffness may progress to involve the arms or face.

In addition to muscular rigidity/stiffness, individuals with SPS also develop muscle spasms, which may occur for no apparent reason (spontaneously) or in response to various triggering events (i.e., stimuli). Spasms can be triggered by unexpected or loud noises, minor physical contact, cold environments, stress or situations that cause a heightened emotional response. Muscle spasms are often very painful and usually worsen existing stiffness. The spasms may involve the entire body or only a specific region. The legs are often involved, which may lead to falls. Spasms of abdominal muscles may lead to individuals feeling full faster than normal (early satiety) leading to unintended weight loss. Spasms involving the chest and respiratory muscles can be serious, potentially requiring emergency medical treatment with ventilatory support. Spasms may last several minutes, but occasionally last for hours. Sudden withdrawal of medication in individuals with SPS may result in a life-threatening situation with overwhelmingly severe muscle spasms. Sleep usually suppresses the frequency of contractions.

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Causes

The exact cause of SPS is not known. Some studies in the medical literature indicate that it may be an autoimmune disorder. Autoimmune disorders are caused when the body’s natural defenses (e.g., antibodies) against “foreign” or invading organisms begin to attack healthy tissue for unknown reasons.

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Most of those affected have antibodies to glutamic acid decarboxylase (GAD), a protein in inhibitory nerve cells that is involved in the creation (synthesis) of the main inhibitory neurotransmitter called gamma-aminobutyric acid (GABA). GABA helps control muscle movement and prevent hyperexcitibility within the brain and spine. The symptoms of SPS may develop when the immune system mistakenly attacks certain nerve cells (neurons) that produce GAD leading to a deficiency of GABA in the body.

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Affected Populations

SPS is an extremely rare disorder. The exact incidence and prevalence of SPS is unknown, although one estimate places the incidence at approximately 1 in 1,000,000 individuals in the general population. The distribution of SPS between men and women indicates a female predominance. SPS usually becomes apparent sometime between 30-60 years of age. However, SPS has been reported to occur in children and older adults as well.

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SPS was first described in the medical literature by doctors Moersch and Woltman in 1956 as stiff-man syndrome. The disorder is now known as stiff-person syndrome to reflect that the disorder affects individuals of any age and both genders.

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Related Disorders

Symptoms of the following disorders can be similar to those of SPS. Comparisons may be useful for a differential diagnosis.

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Tetanus is an infectious disorder that affects the central nervous system. It is caused by the microorganism, Clostridius tetani, a type of bacterium. This microorganism usually enters the body through wounds, injections, or skin ulcers. The incubation period of tetanus is usually seven to twenty one days. Symptoms of this syndrome include muscle stiffness, especially of the jaw (lock jaw) and painful muscle spasms. Affected individuals may also experience low-grade fever, difficulty in swallowing (dysphagia), difficulty breathing, alteration in the rhythm of the heartbeat, and convulsions. Tetanus can also cause behavioral changes including anxiety and restlessness. The symptoms of tetanus usually last for three to four weeks. Although tetanus is a treatable disease, vaccination is recommended during infancy and every few years thereafter.​

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Standard Therapies

The treatment of SPS is directed toward the specific symptoms that are apparent in each individual which often requires a multifaceted approach including non-medication interventions (stretching, heat therapy, aqua therapy, massage therapy, acupuncture, etc). Drugs that are considered GABA-ergic agonists therapies such as benzodiazepines, specifically diazepam and clonazepam, are used to treat muscle stiffness and episodic spasms. Affected individuals may also benefit from baclofen, usually given in addition to benzodiazepines. Other medications reported to have benefit in a small number of individuals include anti-seizure (anticonvulsant) drugs including vigabatrin, valproate, pregabalin, and gabapentin.