Propriospinal myoclonus: a motor phenomenon found in restless legs syndrome different from periodic limb movements during sleep.
Three patients presented with a 25-, 15-, and 5-year history of restless legs syndrome (RLS) and periodic limb movements during sleep (PLMS). For 1, 4, and 5 years, they reported additional involuntary trunk and limbs jerks preceding falling asleep and occasionally during intrasleep wakefulness. Videopolysomnography revealed jerks during relaxed wakefulness arising in axial muscles with a caudal and rostral propagation at a slow conduction velocity, characteristic of propriospinal myoclonus (PSM). Jerk-related EEG-EMG back-averaging did not disclose any preceding cortical potential. During relaxed wakefulness preceding falling asleep and during intrasleep wakefulness, PSM coexisted with motor restlessness and sensory discomfort in the limbs. PSM disappeared when spindles and K-complexes appeared on the EEG. At this time, typical PLMS appeared every 20 to 40 seconds, especially during light sleep stages. PLMS EMG activity was limited to leg, especially tibialis anterior muscles, and did not show propriospinal propagation. In one patient, alternating leg muscle activation was also present. Jerks with a PSM pattern represent another motor phenomenon associated with RLS and different from the more usual PLMS.