Objective measurements and characteristics of spinal excitability in restless Legs syndrome patients
Date
2018
Authors
Dafkin, Chloe Lynn
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Abstract
Restless legs syndrome (RLS) is a neurological disorder that presents with sensory and motor symptoms that worsen in the evening and with rest. An evening state of spinal hyperexcitability has been proposed to be a possible cause of evening increases in RLS symptoms. Therefore the studies included in this thesis aimed to assess circadian variations in the state of spinal excitability in RLS patients in order to extend our knowledge about alterations in spinal processing and provide further elucidation of the pathophysiological mechanisms involved in RLS.
The first two studies of this thesis assessed circadian variations in spinal excitability in terms of spinal reflex responses of RLS patients compared to control participants. The plantar, flexor withdrawal, and crossed extensor reflexes all showed a circadian rhythm in RLS patients suggesting an evening increase in spinal excitability. We theorise that the circadian variation in spinal excitability in RLS patients may be due to an evening form of central sensitization particularly affecting nociceptive responses. These results reinforce the notion that there is increased spinal cord excitability in the evening in RLS patients, which corresponds to the symptomatic period of RLS.
Although RLS patients demonstrated a circadian variation in the reflex responses, indicating a possible increase in spinal excitability in RLS patients in the evening, RLS patients showed no increases in spinal excitability when compared to control participants. An unexpected finding was decreased plantar reflex responses in RLS patients compared to control participants. Excitability of both the flexor withdrawal and crossed extensor reflexes demonstrated no significant differences between RLS patients and control participants. These results do not support the theory of increased spinal excitability in RLS patients. The findings indicate that the pathophysiology of RLS is likely to involve complex spinal
alterations. The concept of global spinal hyperexcitability in RLS patients does not take into account the complex interactions of various sensory modalities in the spinal cord.
The plantar, flexor withdrawal, and crossed extensor reflexes studies in this thesis investigated spinal excitability in RLS patients in a static environment. However, dynamic sensorimotor integration is likely to play a role in RLS as inactivity brings on RLS symptoms and movement relieves RLS symptoms. Therefore, the third study of this thesis investigated temporal changes during locomotion in RLS patients using electromyography (EMG) of the muscles involved in gait in order to evaluate dynamic sensorimotor feedback in RLS patients. EMG muscle activity during the gait cycle did not show the circadian variation in RLS patients that was seen in healthy control participants. However, evening differences in gait muscle activation patterns between RLS patients and control participants were evident. These results extend our knowledge about alterations in spinal processing during gait in RLS patients. A possible explanation for these findings is central pattern generator sensitization caused by alterations in sensitivity of cutaneous afferents in RLS patients.
In conclusion, the results of these studies provide further insight into the pathophysiology of RLS, highlighting that RLS is not due to a global state of spinal hyperexcitability. As not all sensory processing is affected in the same manner the pathophysiology of RLS is likely to involve complex spinal alterations.
Description
Original published work submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy.
Johannesburg, South Africa, 2018.