[A case of alien hand syndrome after right posterior cerebral artery territory infarction].

We report a 63-year-old right-handed man who presented an alien hand syndrome (AHS). He complained of clumsiness of his left hand and admitted to our hospital. On the first examination, he presented left homonymous hemianopia, left spatial neglect and left limb ataxia, but neither paralysis nor sensory impairment. A few days after, he complained that his left hand was controlled by someone else, and we considered this phenomenon as AHS. At that time, he lost sensation of almost all modalities including deep sensation on his left upper and lower limb. Magnetic resonance image examination was performed, and it showed acute cerebral infarction at right posterior cerebral artery territory including right thalamus (ventral posterior lateral nucleus). Generally, AHS is caused by left mediofrontal and callosal lesion (frontal type AHS), or by callosal with bilateral frontal or without frontal lesion (callosal type AHS). However, some cases were reported that they presented AHS after damage of the basal ganglia, right thalamus, right occipital or inferior parietal lobe. Some authors described this phenomenon as "sensory" or "posterior" type AHS. In such cases, included our case, we speculate that sensory impairment causes AHS. Especially in our case, AHS might be caused by not only the sensory impairment but also by left homonymous hemianopia and left spatial neglect. So, because of these symptoms, our patient could not recognize the motion of the left hand, and presented AHS. We think that this "sensory" or "posterior" type AHS should be distinguished from frontal and callosal type AHS.