Neurophysiological correlates of sleep leg movements in acute spinal cord injury

Objective: The objective of this study was to analyze the periodicity of leg movement activity emerging during sleep in a group of patients with spinal cord injury and to evaluate their pathophysiological features.

Methods: Twenty patients (16 males, mean age 34.0 years) with traumatic spinal cord lesions were recruited (5 cervical, 15 thoracic; 16 level A and 4 level B at the American Spinal Injury Association impairment scale). Periodicity of sleep leg movements was analyzed; electroencephalographic spectral analysis and heart rate were evaluated for 20s preceding and 30s following the onset of leg movements.

Results: Periodic leg movements during sleep (PLMS) index >5/h was found in only 4 patients and only 2 of these had PLMS index >15/h. Eleven patients (group I) did not show any increase in heart rate related to the occurrence of leg movements while the remaining 9 did (group II). Two patients in each group had American Spinal Injury Association impairment level B; 5 patients of group I and none of group II had cervical lesions while 6 patients of group I and all 9 of group II had thoracic lesions. Only 2 patients in group I presented clearly periodic leg movements during sleep and PLMS index >15/h. Electroencephalographic delta, alpha and beta bands around leg movements increased clearly in group II while the changes in group I were very limited or absent.

Conclusion: Leg movements during sleep are recorded in spinal cord injury patients with completely absent volitional activity in their lower limb but they show clear periodicity only in a small subgroup of them.

Significance: The disconnection from higher nervous structures, in patients with spinal cord injury might favor the appearance of leg movements due to the activity of spinal generators not inhibited by higher influences; correlated autonomic and electroencephalographic changes can be absent. This motor activity might assume the periodic character when a genetic predisposition is present.