Short-interval leg movements during sleep entail greater cardiac activation than periodic leg movements during sleep in restless legs syndrome patients

Periodic leg movements during sleep (PLMS) are sequences of ≥4 motor events with intermovement intervals (IMI) of 10–90 s. PLMS are a supportive diagnostic criterion for restless legs syndrome (RLS) and entail cardiac activation, particularly when associated with arousal. RLS patients also over-express short-interval leg movements during sleep (SILMS), which have IMI <10 s and are organized mainly in sequences of two movements (doublets). We tested whether the cardiac activation associated with SILMS doublets differs from that associated with PLMS in a sample of 25 RLS patients. We analysed time–series of R–R intervals synchronized to the onset of SILMS doublets or PLMS that entailed an arousal during non-rapid eye movement (NREM) sleep. We assessed cardiac activation based on the R–R interval decrease with respect to baseline during NREM sleep without leg movements. We found that the duration of the R–R interval decrease with SILMS doublets was significantly longer than that with PLMS, whereas the maximal decrease in R–R interval was similar. Scoring SILMS in RLS patients may therefore be relevant from a cardiac autonomic perspective.