StartReact effects support different pathophysiological mechanisms underlying freezing of gait and postural instability in Parkinson's disease

The pathophysiology underlying postural instability in Parkinson's disease is poorly understood. The frequent co-existence with freezing of gait raises the possibility of shared pathophysiology. There is evidence that dysfunction of brainstem structures contribute to freezing of gait. Here, we evaluated whether dysfunction of these structures contributes to postural instability as well. Brainstem function was assessed by studying the StartReact effect (acceleration of latencies by a startling acoustic stimulus (SAS)). We included 25 patients, divided in two different ways: 1) those with postural instability (HY = 3, n = 11) versus those without (HY