UNILATERAL UPPER-LIMB ASTERIXIS RELATED TO PRIMARY MOTOR CORTEX INFARCTION

Background Unilateral upper limb asterixis related to cortical infarct is an unusual clinical picture. We found this association in two pati ents. Magnetic resonance imaging (MRI), somatosensory evoked potential s (SEPs), and electromyographic recording were performed. Case Descrip tions Two patients developed an acute upper limb ataxia with asterixis . This consisted of frequent arrhythmic loss of extensor muscle tone o n instruction to maintain the wrist and fingers extended. Voluntary el ectromyographic activity in the left extensor digitorum communis muscl e showed abrupt periods of interruption ranging from 90 to 260 millise conds in duration in the first case and from 60 to 220 milliseconds in the second case. SEPs were normal. MRI disclosed a right cortical inf arct within the primary motor cortex in both cases. Conclusions These findings indicate that asterixis was not related to a failure in the p rocessing of proprioceptive input controlling the regulation of postur al tone of the distal upper limbs because SEPs were normal. The involv ement of primary motor cortex might suggest that asterixis results fro m an impairment of a centrally generated motor-command signal controll ing the postural tone of the distal upper limb.