Auditory startle reaction is disinhibited in idiopathic restless legs syndrome.

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.