Periodic limb movement disorder: a Trojan horse for residual sleepiness in patients with OSAS while on CPAP?

Abstract

Introduction The main treatment for obstructive sleep apnea syndrome (OSAS) is the application of continuous positive airway pressure (CPAP) with expected resolution of the reported excessive daytime sleepiness (EDS). It is not uncommon though a few of those patients to continue experiencing residual EDS. The aim of this study was to identify the most common causes of the subjectively reported residual EDS. Methods In our tertiary sleep disorders centre and over a 5-year period, OSAS patients on CPAP with residual EDS despite seemingly good control of the apneic events on overnight oximetry and all the efforts for good treatment compliance were retrospectively identified. Eligible patients had an Epworth Sleepiness Scale (ESS) >10, adequate sleep time was demonstrated on sleep diary or actigraphy, and further polysomnographic and clinical history evaluation was required. Results 179 middle aged patients (52.8 ±8.2 years) were identified with an ESS=16 ±3.2 and a BMI=36.4± 6.99 kg/m2. Almost half of our patients (48.6%) (87 patients) were diagnosed with periodic limb movement disorder (PLMD, periodic limb movement index=44.4±28.37 /hr). Half of those (46%)(40 patients) suffered also from restless legs syndrome. 28% of our patients had depression as the primary cause of their residual EDS. 5.1% of the patients were finally diagnosed with concomitant hypersomnia of central origin(narcolepsy and idiopathic hypersomnia). In 6% no cause was identified and their residual EDS was considered to be secondary to possible hypoxic effects to the brain. Conclusion PLMD can be highly prevalent in OSAS with residual EDS while on CPAP.