Stiff Person Syndrome (SPS)

February 2, 2017

Stiff Person Syndrome, also known as Stiff Man Syndrome, is a neurological condition believed to be of auto-immune origin. It is unique among neurological diagnoses due to its lack of significant similarity to any other neurological diseases. Although rare, once observed it is quite unforgettable. Because of its rarity, many neurologists and GPs are not aware of the condition. In most cases, the first symptoms are insidious and victims are often initially misdiagnosed with depression. The onset is most frequent between the third and fourth decades of life.

SPS was the name assigned to the condition when first identified in the 1950s by Moersch and Woltman in the USA. SPS is characterized by fluctuating muscle rigidity in the trunk and limbs and a heightened sensitivity to stimuli such as noise, touch, and emotional distress, which can set off muscle spasms. Abnormal postures, often hunched over and stiffened, are characteristic of the disorder. People with SPS can be too disabled to walk or move, or they are afraid to leave the house because street noises, such as the sound of a horn, can trigger spasms and falls. SPS affects twice as many women as men.   It is frequently associated with other autoimmune diseases such as diabetes, thyroiditis, vitiligo, and pernicious anemia.

The disorder is often misdiagnosed as Parkinson’s disease, multiple sclerosis, fibromyalgia, psychosomatic illness, or anxiety and phobia. A definitive diagnosis can be made with a blood test that measures the level of glutamic acid decarboxylase (GAD) antibodies in the blood. People with SPS have elevated levels of GAD, an antibody that works against an enzyme involved in the synthesis of an important neurotransmitter in the brain.

Women appear most likely to fall victim to SMS/SPS. The age range is wide, with some victims presenting in their teens. However, the majority are aged 30 and over. SMS/SPS has many variants.

Another abnormality in SPS is called co-contraction: when the person attempts to contract a muscle to move in one direction, muscles that pull in the opposite direction are involuntarily activated. Individuals with SPS may have difficulty making sudden movements and may have a stiff-legged unsteady gait (manner of walking). The muscle contractions are usually reduced with extra rest.

Eventually, persons with stiff person syndrome may develop a hunched posture (kyphosis) or a swayback (lordosis).


The cause of stiff person syndrome is unknown, however, researchers theorize that SPS may be an autoimmune disorder. An autoimmune disorder involves a malfunction of the immune system, where the body produces antibodies against its own tissues. Antibodies are proteins produced by the body as part of its defense against foreign bacteria, viruses, or other harmful substances. Other autoimmune disorders such as diabetes, pernicious anemia (a chronic, progressive blood disorder), and thyroiditis (inflammation of the thyroid gland) may occur more frequently in patients with SPS.


Often SPS, antibodies are produced against glutamic acid decarboxylase (GAD), an enzyme largely found in the central nervous system . However, GAD antibodies alone appear to be insufficient to cause SPS, as some persons with stiff person disease do not have the GAD antibodies, and GAD antibodies are associated with a number of diseases.


SPS is characterized by constant painful contractions and spasms of voluntary muscles, particularly the muscles of the back and upper legs.

In general, increased muscle tension, which is more marked proximally than distally, is present. Less frequently, lower extremities are most affected. More rarely, upper and lower extremities are affected. In people with diabetes, one limb may be affected, sparing other muscle groups. In most if not all patients, opposing muscle groups are noted to be tense, and tonic contraction with long relaxation times may be noted following percussion of the muscle. In most patients, the neurologic examination findings are otherwise normal.

Symptoms may occur gradually, spreading from the back and legs to involve the arms and neck. Symptoms may worsen when the affected individual is anxious or exposed to sudden motion or noise. Affected muscles may become twisted and contracted, resulting in bone fractures in the most severe cases.

Individuals with stiff-person syndrome may have difficulty making sudden movements and may have a stiff-legged, unsteady gait. Sleep usually suppresses frequency of contractions. Stiffness may increase and patients may develop a hunched posture (kyphosis) or a swayback (lordosis).


Treatment with IVIg, anti-anxiety drugs, muscle relaxants, anti-convulsants, and pain relievers will improve the symptoms of SPS, but will not cure the disorder. Most individuals with SPS have frequent falls and because they lack the normal defensive reflexes; injuries can be severe. With appropriate treatment, the symptoms are usually well controlled.

SPS is clinically elusive, but potentially treatable. Traditional treatment for SPS starts with medications such as baclofen or a benzodiazepine . Commonly used benzodiazepines are diazepam (Valium) or lorazepam (Ativan). Both benzodiazepine and baclofen act increasing the activity of the central inhibitory systems. Although no studies have been performed, tizanidine (Zanaflex) may be a less sedating alternative, and prednisone is also a commonly prescribed drug for treatment of SPS.

In some patients, plasmapheresis, a process of filtering the blood to remove excess antibodies, has been demonstrated to be useful in removing anti-GAD antibodies from the bloodstream. In the hospital setting, intravenous immunoglobulin (IVIG) has also been used in the treatment of SPS.


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