Progressive Encephalomyelitis With Rigidity: Stiff Person Syndrome Variant Associated With Multiple Sclerosis

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To the Editor: Stiff person syndrome (SPS) is characterized by progressive muscle spasms, rigidity, and hyperlordosis. Progressive encephalomyelitis with rigidity (PER), a variant of stiff person syndrome, is characterized by limb and trunk rigidity, painful muscle spasms, ocular motor disturbances, dysphagia, dysarthria, and hyperekplexia. PER differs from SPS usually based on the presence of brainstem, autonomic, and long-tract signs and also a more aggressive course.