Periodic leg movements during sleep and periodic limb movement disorder in patients presenting with unexplained insomnia

Objective: The aim of this study was to evaluate quantitatively the presence and the characteristics of periodic leg movements during sleep (PLMS) in a group of consecutive patients presenting with daytime impairment related to insomnia of unknown etiology and whose polysomnographic features differ from those of healthy individuals only for a significantly increased arousal index in NREM sleep. Methods: We recruited 20 consecutive adult patients with insomnia according to the ICSD-2 criteria, 20 patients with RLS, and 12 age-matched normal controls. The time structure of their polysomnographically recorded leg movements during sleep was analyzed by means of an approach particularly able to consider their periodicity. Results: A subgroup of 12 patients with a relatively high number of periodic LM activity was detected with a statistically based approach using two indexes: total LM index and Periodicity index. This subgroup had high PLMS index, Periodicity index was also high and PLMS showed a progressive decrease during the night, being highest in the first hours of sleep. The characteristics of PLMS were identical within this insomnia subgroup and RLS patients. Conclusions: PLMS was a common finding in our patients with insomnia and a detailed analysis of their periodicity revealed that a subgroup of these patients had to be finally diagnosed with Periodic Limb Movement Disorder. Significance: Polysomnography with the subsequent analysis of PLMS periodicity is able to differentiate between insomnia patient subgroups.