Dissociation apraxia secondary to right premotor stroke

Apraxia is usually associated with damage to the dominant parietal cortex, but several other areas, including the left dorsolateral frontal cortex and subcortical structures, have also been implicated, suggesting that the praxis system is mediated by an anatomically distributed network. The right premotor frontal cortex is commonly assumed to play a secondary role in this system. We describe a patient who developed left upper limb apraxia after a right premotor ischaemic stroke. The neuropsychological examination ruled out impairment of other cognitive functions, including those subserved by the parietal-temporal cortex. Neither pyramidal signs nor interhemispheric transfer syndrome were detected, suggesting that the right primary motor cortex and corpus callosum were intact and that apraxia arose from a right prefrontal cortical lesion. An additional feature was the patient's inability to copy a gesture or posture demonstrated by the examiner (visual input) or to execute a verbal command (auditory input), even though he could copy the position in which the examiner placed his right arm while blindfolded (proprioceptive input). The disturbance was interpreted as "dissociation apraxia". To our knowledge this type of dissociation has never been reported in a patient with focal brain damage. The case of this patient highlights the importance of the right premotor cortex in the praxis system, and lends support to the hypothesis of a modular and multimodal organization of brain functioning.