n. A rare neurological disorder characterized by progressive rigidity and stiffness, primarily of the axial musculature, resulting in postural deformity.
Stiff person syndrome (SPS), also known as Stiff man syndrome (SMS), is a rare neurologic disorder of unclear etiology characterized by progressive rigidity and stiffness. The stiffness primarily affects the truncal muscles and is superimposed by spasms, resulting in postural deformities. Chronic pain, impaired mobility, and lumbar hyperlordosis are common symptoms. The exact mechanism of the condition is unclear.
SPS occurs in about one in a million people and is most commonly found in middle-aged people. A small minority of patients have the paraneoplastic variety of the condition. Variants of the condition, such as stiff-limb syndrome which primarily affects a specific limb, are often seen.
SPS was first described in 1956. Diagnostic criteria were proposed in the 1960s and refined two decades later. In the 1990s and 2000s the roles of antibodies in the condition became more clear. SPS patients generally have GAD antibodies, which seldom occur in the general population. In addition to blood to tests for GAD, electromyography tests can help confirm the condition's presence.
Benzodiazepine-class drugs are the most common treatment; they are used for symptom relief from stiffness. Other common treatments include Baclofen, intravenous immunoglobin and rituxan. There has been limited but encouraging success with stem-cell treatment.