Objective: Choreic movements of patients with Huntington's disease (HD) may result from an abnormal control of sensory inputs. In order to further examine the pathophysiology of facial choreic movements (FCM), we carried out a neurophysiological study, including prepulse inhibition of the blink reflex (BR), in HD patients with and without FCM.
Methods: The study was conducted in 20 genetically proven HD patients with Unified Huntington Disease Rating Scale (UHDRS) scores of FCM ranging between 0 and 3, and in 12 age-matched healthy volunteers who served as control subjects. We counted the number of spontaneous blinks, recorded the electromyographic activity underlying FCM, and analyzed latency, amplitude, and duration of the BR responses to electrical and auditory stimuli. Prepulse inhibition was studied by comparing the responses to test trials with those to control trials. In control trials BRs were obtained to either a single supraorbital nerve electrical stimulus (EBR) or to a 90dB auditory stimulus (ABR). In test trials, the same stimuli were preceded by the prepulse, which was either a weak acoustic tone or a weak electrical stimulus to the third finger, delivered 30-150 ms before.
Results: Spontaneous blinking rate was abnormally low in 3 patients, and abnormally high in 9 patients. Mean duration of the BR was longer in patients than in control subjects. In prepulse trials, the percentage inhibition of the BR was abnormally reduced in 15 patients to at least one sensory modality, and significantly correlated with the score of FCM.
Conclusions: Our results suggest that the severity of FCM in patients with HD might be an expression of a disturbance in motor control partly related to an abnormal processing of sensory inputs. Such abnormality involves circuits used in prepulse inhibition of the BR.