SPS is a rare progressive neurological disorder characterized by constant painful contractions and spasms of voluntary muscles, particularly the muscles of the back and upper legs. In 1956, scientists at the Mayo Clinic also coined the term stiff man syndrome, and clearly descri stiff person syndrome as a neurological disorder.
The rigidity, which is characterized by tightness and stiffness, begins slowly over several months at the axial muscles, especially the thoracic and lumbar spine, and spreads to the legs. The stiffness 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 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.