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

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).

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.

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 APB and TA muscles. The average of 5 to 10 trials at each site was obtained and compared using Student's t-test.

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 APB (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.

The supraspinal inhibitory system is impaired in pRLS.