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a condition of unknown etiology marked by painful, progressive fluctuating rigidity of axial and limb muscles in the absence of signs of cerebral or spinal cord disease but with continuous electromyographic activity.
a condition of unknown cause characterized by progressive fluctuating rigidity of axial and limb muscles in the absence of signs of cerebral and spinal cord disease but with continuous electromyographic activity.
Aetiology Autoimmune disorder linked to production of anti-GAD65 antibodies against glutamic acid decarboxylase in 60% of patients and pancreatic islet cells; remaining 40% have other autoantibodies. It is unclear whether anti-GAD antibodies cause the loss of spinal inhibition. Some patients with cancer-related stiff-person syndrome have autoantibodies against a 128 kD synaptic protein
Diagnosis Simultaneous video-electroencephalographic surface EMG demonstrates continuous motor unit activity in affected muscles at rest, abnormal activity of small gamma motor neurons
Management Benzodiazepines, cortisol if adrenocortical dysfunction, plasma exchange, IVIG—IV immunoglobulins are well-tolerated and effective
Associated disorders Epilepsy, type 1 diabetes and other organ-specific autoimmune disorders—e.g., myasthenia gravis, thyroiditis, adrenalitis