Respiratory burden and periodic limb movement frequency in adults with elevated PLMI: A retrospective...

Periodic limb movements during sleep (PLMS) frequently coexist with obstructive sleep apnea (OSA), and whether PLMS should be scored when OSA is untreated remains unclear. In adults with an elevated periodic limb movement index (PLMI), we primarily examined whether the apnea-hypopnea index (AHI) was associated with PLMI; secondary analyses assessed its associations with the PLM-arousal index (PLMAI) and PLM-arousal coupling.

We retrospectively analyzed polysomnograms of 507 consecutive adults with PLMI ≥15 events/h. Associations of respiratory and oxygenation measures with PLMI were assessed using Spearman correlation, adjusted regression of log-transformed PLMI, and categorical analyses across OSA severity. PLMAI was modeled using mean-centered PLMI and AHI, their interaction, age, sex, and body mass index, with heteroscedasticity-robust (HC3) inference and sensitivity analyses.

AHI was not associated with PLMI (ρ = 0.003; 95% CI -0.08 to 0.09). After adjustment for age, sex, and body mass index, PLMI changed by -0.2% per 10 events/h of AHI (95% CI -2.2% to 1.8%). PLMI did not differ across OSA severity categories (p = 0.63), and AHI did not predict PLMI >30 events/h (OR per 10 events/h 1.05; 95% CI 0.98-1.12). AHI showed no independent main association with PLMAI (p = 0.08), but the PLMI×AHI interaction was positive and remained significant across sensitivity analyses (HC3 p < 0.001).

In adults with elevated PLMI, respiratory burden was not associated with PLM frequency, supporting continued scoring and reporting of PLMS in patients with OSA. Higher AHI modestly strengthened the association between PLMI and PLM-related arousals; therefore, PLMAI should be interpreted cautiously when the respiratory burden is substantial.