Alien hand syndrome: Pathophysiology, semiology and differential diagnosis with psychiatric disorders (Review)

Alien hand syndrome (AHS) is an uncommon neurological condition characterized by involuntary, yet seemingly purposeful, movements of a limb, typically an upper extremity, with variable awareness and control by the affected individual. It is associated with a range of peculiar sensations, such as the feeling of limb estrangement, alien control and involuntary mirroring or restraining of movements. AHS indicates a profound disruption in volitional motor control and personal agency. The aetiology of AHS is the dysfunction of critical brain regions secondary to diverse neurological insults, such as tumours, vascular disorders, infarction or neurodegenerative diseases. It is clinically categorized into the parietal and callosal types, depending on the affected region, with manifestations often linked to the specific brain region affected. The callosal type is particularly challenging to diagnose due to its rarity and potential for nonspecific or concealed symptoms amid concurrent brain injuries. Distinguishing AHS from psychiatric disorders is crucial for accurate diagnosis and improved patient outcomes. Further research is imperative for a deeper understanding of the pathophysiology of AHS and the development of effective treatments. AHS predominantly affects adults and is frequently associated with multiple comorbidities. The syndrome is also exemplified by three distinct motor behaviours: Involuntary grasping, inter-manual conflict and limb levitation accompanied by the sensation of an alien limb or the perception of external control over one's movements. It has a generally good prognosis with partial or total recovery following appropriate rehabilitation techniques, including pharmacological and psychological measures.