Parkinson's disease (PD) and focal dystonia (FD) are both predominantly characterized by motor symptoms. Also, recent research has shown that sensory processing is impaired in both movement disorders. FD is characterized by involuntary movements and abnormal limb postures; thus, abnormal kinesthesia could be involved in the pathogenesis. We examined passive index finger movements in patients with FD (n = 12) and PD (n = 11) and in age-matched healthy controls (n = 13). Compared to healthy controls, patients with PD and FD were significantly impaired in the correct detection of the movement direction. The perceptual thresholds for 75% correct responses of movement direction were 0.21 degrees for FD and 0.28 degrees for PD patients compared to 0.13 degrees in control subjects. Subjects with PD and FD were also significantly impaired when they had to judge consecutive amplitudes. Results of the present study point to impaired kinesthesia in FD. Defective sensory processing could be involved in the pathophysiology of the disease and may influence dystonic contractions.

The auditory startle response (ASR) is a brainstem reflex elicited by an unexpected acoustic stimulus. In focal dystonia (FD), the excitability of brainstem neurons is abnormally enhanced. To identify a possible impact of this pathology on the processing of acoustic stimuli, we studied the habituation of the ASR in patients (n = 11) with FD and compared the findings to those of patients with Parkinson’s disease (PD; n = 11) and controls (n = 11). Latencies in FD patients did not differ from those of controls but were delayed in PD patients compared to controls (p < 0.0001). Habituation was normal at the orbicularis oculi muscles but reduced at the sternocleidomastoid muscles in FD (p = 0.005). Habituation in PD was comparable to controls. Normal latencies and sequence activation indicate intact neural pathways mediating the ASR in FD. Impaired habituation of the ASR points towards a reduced inhibition of acoustic stimuli in FD.

No abstract

No abstract