S138 Sensory tricks, startle and prepulse inhibition in blepharospasm

Abstract

Objectives Dystonia is a disorder that manifests as an involuntary muscle contraction that may be generated by abnormal processing of sensory inputs. Abnormalities of motor control occur mainly in circuits of some complexity. An important feature in blepharospasm (BSP) is the need for a fine control of the level of eye closure, which may be abnormal in BSP patients. Methods We have examined the response of the orbicularis oculi (OOc) to various external interventions. For the study of the blink reflex, electrical stimuli were applied to the supraorbital nerve of each side or mechanical stimuli were applied to glabella and chin. For the study of prepulse inhibition, a conditioning electrical prepulse was applied to the median nerve or auditory stimuli were delivered 100 ms prior to the supraorbital nerve shock. For a startle, a loud auditory stimulus was delivered unexpectedly or together with an imperative somatosensory signal carrying the instruction to react either closing or opening the eyes. Results The blink reflex was abnormally larger and was inhibited less by a prepulse in patients than in healthy subjects. The degree of prepulse inhibition correlated with the degree of transient alleviation of BSP with a sensory trick. A startle sound together with the instruction to react accelerated reaction and movement times in closing and opening the eyes in both healthy subjects and patients. Discussion The combination of various electrophysiological tests characterize the clinical phenomenology in patients with BSP. Conclusion Prepulse inhibition in BSP patients correlate with the benefit of sensory tricks.