Changes in excitability of motor cortical circuitry in primary restless legs syndrome

Objective: To investigate the excitability of segmental and suprasegmental systems in patients with primary restless legs syndrome (pRLS) by measuring the cortical silent period (C-SP) and the peripheral silent period (P-SP). Background: There is some evidence that RLS may be the motor manifestation of normal CNS periodicity that becomes disinhibited under certain conditions. The mechanism of this disinhibition is unclear. Design/Methods: Ten patients with pRLS and 10 normal age-matched subjects were studied. The mixed nerve P-SP produced by electrical stimulation of the median and common peroneal nerves was recorded during maximal contraction of the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The C-SP produced by a single magnetic shock to motor cortex at 150% of resting threshold was also measured during maximal contraction of the APE and TA muscles. The average of 5 to 10 trials at each site was obtained and compared using Student's t-test. Results: Resting central motor threshold was not significantly different between pRLS patients and the control group. The average duration of the C-SP was shorter in the APE (74.5 +/- 37.7 versus 129.56 +/- 35.95 msec, p < 0.05) and TA (66.81 +/- 25.63 versus 136.1 +/- 40.35 msec, p < 0.05) in patients with pRLS. The P-SP duration, however, was not significantly different between two groups in either limb. Conclusion: The supraspinal inhibitory system is impaired in pRLS.