Narcolepsy 'masked' in a patient with severe obstructive sleep apnea

Narcolepsy is a rare hypersomnolence disorder with a prevalence of 25-50 per 100000 population.Narcolepsy frequently co-exists with obstructive sleep apnea (OSA) and the diagnosis remains elusive in view of overlapping symptoms. In this case report, we present an atypical case of Narcolepsy which was unmasked in the titration study as respiratory events-related arousals were abolished. Case history and discussion: A 53-year-old male was referred to our sleep clinic in view of persisting excessive daytime sleepiness (EDS) despite using positive airway pressure(PAP) therapy adequately for severe OSA. On retaking clinical history, the patient had EDS history for 25 years and had episodes of buckling of knees and irresistible sleep while standing in lifts and riding a bicycle. His sleep assessment revealed Epworth sleepiness score of 18/24 with a BMI of 32.2 kg/m2. Level 1 polysomnography revealed a sleep efficiency of 94.5% despite fragmented sleep. Sleep latency was 2minutes and REM latency was 1hour 29 minutes. Apnea-hypopnea index was 30.3 events/hr. In the in-lab titration study the respiratory events and arousals were abolished and REM latency was shortened to 22 minutes. A multiple sleep latency test (MSLT) with PAP therapy at adequate pressures revealed sleep-onset-REM periods with a mean latency of 7 minutes. Though the history was highly suggestive of narcolepsy, the diagnosis would have been elusive if not for the shortened REM latency revealed with PAP therapy. Conclusion: Narcolepsy needs to be considered in patients with residual significant EDS. Titration data needs to be carefully analyzed for typically shortened REM latency. Confirmation of diagnosis with MSLT is warranted in patients with typical history.