Clinical and polysomnographic characteristics of high frequency leg movements

The aim of this study was to describe the clinical and polysomnographic characteristics of patients with high frequency leg movements (HFLM) on polysomnographic recording.

Among 486 patients (male 232, female 254) referred for overnight diagnostic PSG over a 9-month period, 37 patients demonstrated HFLM: 19 males (8.2% of PSGs) and 18 females (7.1% of PSGs). An equal number of age- and sex-matched consecutive patients who did not show HFLM were selected. HFLM was defined as > or = 4 discrete leg movements occurring at a frequency of 0.3-4.0 Hz.

Two-thirds (64.3%) of all HFLMs occurred during waking; 35.7% occurred during sleep. Of those HFLM episodes occurring during sleep, 44.8% occurred during stage 1, 45.1% during stage 2, 0.6% during stages 3 and 4, and 9.5% during REM. The movements usually appeared unilaterally, but sometimes they showed a bilateral pattern. The mean frequency was 1.6 +/- 0.6 Hz (range 0.4-3.7), the mean number of episodes of HFLM per subject per night was 26.5 +/- 30.5 (range 2-111), and the mean duration per episode was 17.6 +/- 35.4 sec (range 1.5 sec-6.1 minutes). The mean HFLM index, (total number of HFLM divided by the time in bed, in hours), was 107.7 +/- 254.5 (range 2.0-1078.3). Patients with HFLM complained of RLS symptoms significantly more often than the group without HFLM (p < 0.05).

Further studies are needed to establish criteria for scoring HFLM. Examination of other patient cohorts with HFLM will be needed to determine whether HFLM are in fact associated with RLS.