Unmasking of Periodic Limb Movements With the Resolution of Obstructive Sleep Apnea During Continuous Positive Airway Pressure Application

Purpose: Periodic limb movements (PLMs) and obstructive sleep apnea (OSA) may present as overlapping conditions. This study investigated the occurrence of PLM during continuous positive airway pressure (CPAP) titration, with the hypothesis that the presence of PLM during CPAP represented "unmasking" of a coexisting sleep disorder. Methods: A total of 78 polysomnographic recordings in 39 OSA subjects with an hourly PLM index >= 5 during CPAP application were evaluated. Results: Application of CPAP significantly improved sleep architecture without change in the PLM index when compared with baseline. The PLM indices and PLM arousal indices were linearly correlated during both nights (r = 0.553, P < 0.01; r = 0.548, P < 0.01, respectively). Eleven subjects with low PLM indices at baseline had greater changes in the PLM index as compared with the sample remainder (P = 0.004). Sixteen subjects with significantly lower PLM indices at baseline required optimal CPAP levels higher than the sample average of 8.2 cm H2O (P = 0.032). These subjects also showed significantly higher median apnea-hypopnea index (AHI) at baseline than the sample remainder (74.4 events per hour [range: 24.2-124.4 events per hour] vs. 22.7 events per hour [range: 8.6-77.4 events per hour], respectively, P < 0.001). Conclusions: These findings suggest that PLM seen during CPAP titration may be related to a concurrent sleep disorder because of "unmasking" in patients with treated OSA.