Study objectives: Because the auditory startle reaction is abnormal in disorders with substantia nigra pathology, we hypothesized that auditory startle responses (ASRs) might also be altered in restless legs syndrome (RLS).
Design: Neurophysiologic study of the auditory startle reaction.
Setting: Neurology departments of a university hospital and an affiliated local hospital.
Patients and participants: Fifteen patients with idiopathic RLS (6 de novo, 9 untreated after a 7-day wash-out period of levodopa, mean duration of RLS [corrected] symptoms 21.2 +/- 17.9 years, mean IRLS [corrected] severity score 23.5 +/- 6.7) and 15 sex- and age-matched healthy controls were investigated.
Interventions: Not applicable.
Measurements and results: ASRs were elicited by 8 high-intensity auditory stimuli differing randomly in tonal frequency and intensity. Reflex electromyographic activity was simultaneously recorded with surface electrodes from 8 facial, neck, arm, and leg muscles. In RLS patients, ASRs were significantly more frequent (541 of 960 possible responses; controls, 430 of 960), and ASR area under the curve was significantly larger (3812 +/- 450 microVms; controls, 1756 +/- 226 microVms). Analysis per body region revealed that ASRs were significantly more frequent in RLS patients than in controls in leg muscles (138/360 vs 55/360); ASR latencies to leg muscles were significantly shorter in RLS patients (129 +/- 6 ms vs 160 +/- 11 ms); ASR area under the curve was significantly larger in RLS patients in facial (7547 +/- 1326 mmicroVms vs 2982 +/- 448 microVms) and leg muscles (1373 +/- 308 microVms vs 541 +/- 193 microVms).
Conclusions: Our data demonstrate disinhibition of reticulospinal pathways in RLS patients as compared to normal controls, likely originating from dysfunction rostral to the lower brainstem.