Stiff person syndrome (SPS) (or stiff-man syndrome outside the USA) is a rare neurologic disorder of unknown etiology.
Those with the illness experience progressive, fluctuating tonic muscle contractions, particularly the axial musculature. Depression and anxiety are often noted although this may be a result of discomfort due to stiffness, rather than underlying neurochemical abnormalities. MRI detection of GABA in the brain have demonstrated reduced levels in stiff-person syndrome
Because many patients with SPS have circulating antibodies to the enzyme glutamic acid decarboxylase (GAD), an autoimmune cause of the disease has been postulated. However, GAD antibodies cannot be the sole cause, as most Type I diabetics possess anti-GAD antibodies, yet the frequency of SPS among Type I diabetics is 1 in 10,000. The GAD protein regions (epitopes) recognized by these antibodies may differ in each disease.. A mutation in GLRA1 (glycine receptor) is responsible for some cases of stiff person syndrome.
Prognosis is variable and there is no reliable predictor of speed and severity of disease onset. Muscle tetany may lead to muscle rupture and broken bones, or problems swallowing and breathing in severe cases.
Treatment is mostly palliative with muscle relaxants which enhance GABA production, such as benzodiazepines. These treatments lose their effectiveness as the illness progresses. In the absence of double-blind, placebo-controlled class A trials to determine treatment efficacy, some authorities recommend human trials of immunosuppressive therapy, plasmapheresis or intravenous immunoglobulin infusion. A recent study funded by the NINDS demonstrated the effectiveness of intravenous immunoglobulin (IVIg) treatment in reducing stiffness and lowering sensitivity to noise, touch, and stress in people with SPS. Monoclonal antibody rituximab has produced long-lasting remissions. Clinical trials of this treatment are underway. A clinical case was reported in April 2008 issue of the Neurology Journal. The patient's symptoms improved unexpectedly from propofol administration.[