Periodic limb movements in complete spinal cord injuries: Important new insights into the pathophysiology of this symptom

Abstract

Objective Periodic limb movements (PLM) are automatic stereotyped movements of the lower limbs which occurs predominantly at night or when lying down. In a previous study, we identified PLM in numerous patients with spinal cord injuries (SCI), falsely labeled as spasticity and spasms. But unlike spasticity and flexor afferent reflex, the pathophysiology of this movement disorder remains unclear, whether it has a cerebral or spinal origin. Material/Patients and methods Patients with a history of SCI and consecutively addressed for uncontrolled spasticity and spasms despite treatment from March 2014 to July 2016, were systematically assessed by a nocturnal polysomnography (PSG). PLM were defined as a PLM index above 15 events per hour of sleep, according to AASM guidelines. We extracted the data regarding patients presenting with a clinically complete SCI, defined as an ASIA impairment scale scored as A (AIS-A). Results Among the 24 patients initially included, 4 were AIS-A. They all had a thoracic level of injury above Th10. They were all diagnosed with PLM, with a median PLM index of 53.5/h (range [18.2;155]), and PLM arousals of 2.2/h (range [0;15.9]). The initiation of a dopaminergic agonist restored normal sleep motor behaviors in all 4 patients. Discussion/Conclusion The fact that PLM were observed in patients with a clinically complete disruption of the spinal cord, strongly suggested that these movements originates within the spinal cord, possibly below Th10. This hypothesis has been previously raised by the observation of persistent PLM during REM sleep in incomplete SCI patients. We therefore hypothesize the existence of a spinal generator of PLM, at least partly made up by dopaminergic neurons expressing D3 dopa-receptors. This sets the bases for future anatomical and physiological studies for the origination of these movement disorders.