The alien hand and related signs

Abstract

Alien limb sign includes failure to recognise ownership of one's limb when visual cues are removed, a feeling that one body part is foreign, personification of the affected body part, and autonomous activity which is perceived as outside voluntary control. Although the hand is most frequently affected, any limb or combination of limbs may fulfil the alien limb criteria. Alien hand sign should be reserved for cases in which the hand feels foreign together with observable involuntary motor activity. To characterise this phenomenon, seven patients with alien hand sign and other motor or behavioural manifestations are described. Aetiologies included multiple infarcts and cortobasal ganglionic degeneration (CBD). In this study, all patients had apraxia in response to verbal commands and problems with bimanual coordination. Most displayed non-goal directed involuntary motor activities, and two had self destructive motor behaviours. Grasp reflex occurred with alien hand due to either aetiology. Cortical reflex myoclonus was frequently seen in CBD patients. The phenomenological spectrum is reviewed, a diagnostic protocol proposed, and possible anatomical bases of alien hand discussed.