Sleep-related leg movements in obstructive sleep apnea: definitions, determinants, and clinical consequences.

Study Objectives: To investigate (1) the effect of different scoring rules on leg movement (LM) classification in patients with obstructive sleep apnea (OSA); (2) determinants of respiratory event related leg movements (rLM); and (3) to relate LM parameters to clinical outcomes.

Methods: (1) LM classification was compared between the World Association of Sleep Medicine (WASM) 2006 and the WASM 2016 rules in 336 participants with apnea hypopnea index (AHI) ≥ 5; (2) determinants and features of rLM were investigated with logistic mixed regression in 172 participants with AHI ≥ 10 and respiratory disturbance index (RDI) ≥ 15, and (3) LM parameters were compared for patients with and without cardiovascular events and related to continuous positive airway pressure (CPAP) adherence.

Results: WASM-2016 scoring significantly reduced periodic limb movements of sleep (PLMS) frequency in OSA participants even when only considering the new periodicity criteria. Probability of rLM was strongly increased when respiratory events ended with an arousal, but rLM probability was lower for hypopneas and respiratory effort-related sleep arousal (RERAs) than for obstructive apneas. In participants with frequent non-respiratory PLMS, rLM were more frequent and behaved more PLMS-like. In participants without PLMS, rLM probability mostly depended on respiratory event features. LM parameters were neither related to cardiovascular event risk nor to CPAP-adherence.

Conclusions: It is likely that the PLMS frequency in OSA populations has been previously overestimated. Our results suggest that there are two types of rLM, true periodic ones that happen to synchronize with the respiratory events, and periodic appearing but respiratory driven LM, and that the presence of non-respiratory PLMS is instrumental in distinguishing between the two.