Contributed by Kailash Bhatia, MD
Institute of Neurology
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Stiff person syndrome (SPS), first described by Moersch and Woltman in 1956, is a rare progressive movement disorder characterized by involuntary painful spasms and rigidity of muscles, usually involving the lower back and legs. This results in a typical clinical picture of stiff-legged gait with exaggerated lumbar hyperlordosis.
Onset is usually in the third to fifth decades of life. Investigations reveal a characteristic abnormality on EMG recordings with continuous motor unit activity of the paraspinal axial muscles. Variants of stiff person syndrome include "stiff-limb syndrome" producing focal stiffness typically affecting distal legs and feet.
Another variant is "stiff-person syndrome plus encephalomyelitis." There are also other causes of stiff or rigid limbs including neuromyotonia apart from the well recognized extrapyramidal rigidity and spasticity in pyramidal dysfunction.
Structural MRIs of brain and spine are usually normal. The exact cause of classic SPS remains unknown but automimmune mechanisms are suspected to have a role. Antibodies to the enzyme glutamic acid decarboxylase (GAD), have been detected and other autoimmune disorders such as diabetes, pernicious anemia, and thyroiditis occur more frequently in patients with SPS. 60-90% of classic SPS patients have very high anti-GAD titres, (usually over 20 nmol/l). Another important association is that of SPS with paraneoplastic syndromes. Mutations of the GLRA1 (glycine receptor) gene have also been identified to account for some cases of startle and limb stiffness.
Therapy for SPS remains symptomatic with muscle relaxants with GABAergic action. Immunosuppressive therapies include plasmapheresis or intravenous immunoglobulin infusion. However, overall the experience is still limited and there are yet no double-blind, placebo-controlled class A trials regarding treatment efficacy. The prognosis is variable. No reliable predictor of the disease course has been identified.