The stiff man and stiff man plus syndromes

Rigidity in the setting of continuous motor unit activity at rest can be ca used by a variety of central and peripheral conditions. A central origin is suggested by the presence of painful reflex spasms. Focal spinal lesions a nd infective causes are relatively easily excluded through imaging, microbi ological and serological studies. There then remain a group of-patients who may have the classical 'stiff-man syndrome' or a related syndrome. When st rict diagnostic criteria are used, patients with the stiff man syndrome uni formly have axial rigidity, and about 90% are found to have antibodies agai nst glutamic acid decarboxylase. Treatment response and prognosis are excel lent. Stiff persons with 'plus' signs, particularly those with rigidity of a distal limb, are unlikely to have the classical stiff man syndrome. They have a poorer treatment response and prognosis. Some have a paraneoplastic aetiology, while a non-malignant autoimmune basis seems likely in others. T hose in whom post-mortem pathology findings are available usually are seen to have had an encephalomyelitis with prominent involvement of the grey mat ter. Clinically, stiff persons with 'plus' signs may be divided into three groups according to the aggressiveness of the pathology and its relative di stribution. Encephalomyelitis with rigidity follows a relentless subacute c ourse, leading to death within 3 years. Chronic cases may present with pred ominantly brainstem involvement, including generalised myoclonus (the 'jerk ing stiff person syndrome') or spinal cord involvement, dominated by stiffn ess and spasm in one or more limbs (the 'stiff limb syndrome').