Alien hand syndrome without a corpus callosum lesion.

A 58 year old right handed woman developed a left alien hand syndrome after a right capsulothalamic haemorrhage with mesencephalic extension. No lesion was detected in the corpus callosum. Positron emission tomography suggested that right cortical dysfunction might account for the absence of recognition of the left hand whereas involuntary motor activity was attributed to the lesion itself. This case shows that the alien hand syndrome is not always the expression of a disconnection syndrome and may occur after a large, strategically located, posterior lesion.