Reflex testing reveals circadian variation of spinal excitability in restless legs syndrome patients

Authors


Ms Samantha Kerr, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand Medical School, 7 York Road, Parktown, 2193, South Africa. Email: samantha.kerr@wits.ac.za

Abstract

Restless legs syndrome (RLS) is a condition characterized by night-time exacerbation of symptoms, suggesting a possible circadian aetiology. It is hypothesised that RLS is caused by a central deficiency of dopamine causing spinal hyperexcitability. The study objective was to compare spinal reflex responses in RLS patients at two different times and with healthy participants. Standard electromyographic (EMG) techniques were used to quantify patellar and H-reflexes in RLS patients (n= 11) and matched control subjects (n= 9). Kinematic analysis was performed on patellar reflexes to measure knee angular velocity and displacement. Both reflexes were tested in the evening and the following morning. RLS patients had a significantly attenuated evening quadriceps EMG amplitude during patellar reflex testing compared to morning measurements (p= 0.0078) and compared to evening measurements in the control group (p= 0.040). Also, the RLS patients had significantly less knee angular displacement in the evening compared to morning measurements (p= 0.018). There were, however, no significant differences in any of the H-reflex measurements. Our data confirm a circadian variation in RLS aetiology but found no evidence of global spinal hyperexcitability as measured by patellar and H-reflex assessment. Differences in the findings from patellar and H-reflex assessments may indicate discrete (non-uniform) changes in the excitability of the spinal cord function amongst RLS patients.

Ancillary