Falling and postural deficits due to acute unilateral basal ganglia lesions.

Nine patients presented with sudden falling events to one side while sitting, standing, or walking. All were initially unaware of their severe postural deficit, and five were obfuscated. The observed falls were a distinctly slow, tilting motion in a stereotypic lateral or diagonal trajectory, literally "like a falling log." The events occurred with eyes opened and were exacerbated with eye closure, but no patient had evidence of cerebellar, vestibular, or posterior column dysfunction or significant motor weakness. Unilateral basal ganglia hemorrhages or lacunar infarcts contralateral to the side of the fall were demonstrated by computed tomographic scans. The overall prognosis was favorable; eight of nine patients regained independent ambulation within 3 to 6 weeks. Our findings indicate that a distinct loss of postural balance arises contralaterally to unilateral pallidal-putaminal lesions.