Nasal Continuous Airway Pressure Titration Unmasks Periodic Limb Movements in Obstructive Sleep Apnea Syndrome

Park, D H; Jeong, D U

Abstract

OBJECTIVES
High co-morbidity of periodic limb movements during sleep(PLMS) and obstructive sleep apnea syndrome(OSAS) is well known and their incidences tend to increase in the elderly. Previous studies have inconsistently reported increase or no change of periodic limb movement index(PLMI) by nasal continuous positive airway pressure(CPAP) in OSAS without annalyzing possible variables affecting PLMI. We attempted to examine PLMI change evoked during CPAP titration and also factors affecting it in OSAS.
METHODS
Twenty-nine OSAS patients(M:F=26:3, mean age:51.6+/-10.6 yrs) without other sleep disorders except for PLMS were selected, based on the nocturnal (baseline) polysomnography. Another night of nocturnal polysomnography was performed for CPAP pressure titration. We compared between those two nights PLMI, mean and lowest SaO2, and sleep variables. We also calculated PLMI differences between baseline and CPAP nights, named as delta PLMI(value of CPAP night PLMI minus value of baseline night PLMI). Correlations were calculated between delta PLMI and factors such as age, body mass index, applied CPAP pressure, baseline night values of respiratory disturbance index, mean and lowest SaO2, and sleep parameter differences between baseline and CPAP nights.
RESULTS
Decrease of RD1(p<.01) and increase in mean and lowest SaO2(p<.05, p<.01) were observed during CPAP night. No sleep parameters showed significant change except for the decrease of total stage 1 sleep%(p<.01) during CPAP night. Ten out of 29 patients showed PLMI increase, while the other 19 patients showed either no change(n=14) or even PLMI decrease(n=5) during CPAP night. The 10 patients showing PLMI increase during CPAP night showed a significant positive correlation between delta PLMI and baseline night RDI(p<.05), which meant that PLMI increase was found to be more prominent in higher RDI patients than in lower RDI ones. There were no significant correlations between delta PLMI and other factors in the other 19 patients.
CONCLUSIONS
We suggest that during the baseline night PLMS would have been underscored and/or masked due to the overlapping of PLMS and apnea/hypopneas or the arousals induced by apnea/hypopneas. Despite its still unknowen mechanism, the CPAP application may unmask PLMS and increase PLMI in a subgroup of OSAS patients. It needs to be evaluated further whether the chronic CPAP use sustains the above findings