Stiff-Person Syndrome

What is Stiff-Person Syndrome?

Stiff person syndrome is a rare neurological disorder that causes painful muscle spasms and rigidity in the muscles. Stiff person syndrome is also known as SPS, stiff man syndrome and Moersch-Woltman syndrome.

What causes stiff person syndrome?

The cause of stiff-person syndrome is not fully understood. It is thought that it may be an autoimmune disorder, which means that the body’s defence mechanism (the immune system) attacks healthy tissue, believing it to be a harmful threat. It is not known why autoimmune conditions occur.

Investigations suggest that most people who have stiff person syndrome have GAD (glutamic acid decarboxylase) antibodies. GAD is a protein found in the nerve cells. It helps to produce GABA (gamma-aminobutyric acid), which is involved in muscle movement control. It is thought that stiff person syndrome may occur when the body mistakes the neurons that are involved in GAD production, leading to a shortage of GAD. In some cases, individuals also have antibodies for amphiphysin, a protein involved in the transmission of electric signals between the nerve cells. This is less common than GAD antibodies and it tends to be present in people with breast cancer.

In cases where antibodies for GAD are not present, the case may be idiopathic (no known cause) or testing may be carried out to identify other potential causes.

How is stiff person syndrome diagnosed?

Stiff person syndrome is diagnosed based on clinical symptoms and the findings of physical examinations and additional tests, which may include tests to identify specific antibodies and those to monitor electrical activity in the nerve cells. Electromyography (EMG) shows muscle activity during both rest and work. If the muscles appear stiff and rigid, this is symptomatic of stiff person syndrome.

What are the symptoms of stiff person syndrome?

SPS affects people in different ways and some people have much more severe symptoms than others. The main characteristics are painful muscle spasms, which are accompanied by progressive rigidity. Often, symptoms develop over a period of time and then stabilise before progressing. In the most severe cases, the muscles become so stiff that mobility is compromised and the spine becomes hunched. The hips, knees and shoulders can be affected, as well the lower back.

In addition to stiffness, it is common for individuals to experience muscle spasms, which may come on very suddenly or as a result of response to a trigger, such as stress or physical contact with a surface or object. Sometimes, unexpected spasms can also make stiffness worse, as well as increasing the risk of falls and affecting digestion and appetite when the abdominal muscles are involved. If spasms affect the respiratory muscles, this can be very serious and often, immediate medical attention is required. Spasms vary in severity, can affect part or the whole of the body and can last anywhere from minutes to hours. If medication is stopped abruptly, this can lead to severe spasms that can be life-threatening.

In more severe cases, stiff person syndrome can affect day to day life and make even the most basic and mundane activities difficult. In this case, it may be beneficial to use a walking aid. Problems with mobility can also affect mental health. Some people become very anxious about going out on their own or having to complete actions such as crossing the road or climbing onto a bus or train, for example. If the condition is not treated effectively, it is possible for serious complications to arise, such as breathing difficulties.

Less commonly, stiff person syndrome may be associated with thyroiditis, pernicious anaemia, epilepsy and a skin condition called vitiligo.

Subdivisions of stiff person syndrome There are variants of stiff person syndrome that tend to be a lot less common than the conventional form. These include:

  • Jerking stiff-person syndrome: this is characterised by sudden, jerky movements in the legs and progressive stiffness
  • Stiff limb syndrome: this causes stiffness and spasms in one leg only. However, as the disorder progresses, both legs may be affected
  • Progressive encephalomyelitis with rigidity and myoclonus (PERM): this is characterised by symptoms similar to classic stiff person syndrome. However, symptoms tend to progress much faster

Who is affected?

Stiff person syndrome is rare. It is estimated to affect just 1 in every 1 million people, although the exact incidence is unknown. This disorder is more common in females than males and is most commonly diagnosed in people aged between 30 and 60 years old. However, it can be found in younger people and children.

How is stiff person syndrome treated?

Treatment is designed to target the main symptoms and may involve a combination of medication and therapies, such as physiotherapy. Medicines such as benzodiazepines are used to reduce stiffness and treat muscle spasms. In addition, baclofen and drugs used to treat and control seizures may be recommended.

IVIG (intravenous immunoglobulin) treatment may also be beneficial, but further research is required to determine the efficacy and safety of this therapy for people who have stiff person syndrome.

Research into potential therapies and treatments is still ongoing.

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