Increased brainstem excitability in stiff-person syndrome.

The recovery cycle of the R2 component of the blink reflex was studied in five patients with stiff-person syndrome (SPS) and in seven healthy control subjects. R2 recovery was enhanced in patients with SPS. This result is suggestive of hyperexcitability of brainstem interneuronal circuits in SPS. Hyperexcitability may result from abnormal input from suprasegmental structures or loss of inhibition by interneurons and is compatible with the proposal that there is a widespread dysfunction of central inhibitory mechanisms in SPS.