High-altitude global amnesia.

A variety of transient focal neurological signs presenting at high altitude have been described without associated acute mountain sickness or other concurrent illness. We report a case series of transient global amnesia at high altitude. The term high-altitude global amnesia (HAGA) is introduced to indicate this condition, and the pathophysiology is discussed. We hypothesize that because of the highly variable ventilatory response to hypoxia and to individual cerebral vasomotor reactivity, individuals with a marked hyperventilatory response could experience significant hypocapnic cerebral vasoconstriction that in turn could cause local hypoxia or ischemia to particular regions of the brain and resulting transient focal neurological impairment.