The role of home sleep testing for evaluation of patients with excessive daytime sleepiness: focus on obstructive sleep apnea and narcolepsy

Excessive daytime sleepiness (EDS) is a common complaint in the general population, which may be associated with a wide range of sleep disorders and other medical conditions. Narcolepsy is a sleep disorder characterized primarily by EDS, which involves a substantial burden of illness but is often overlooked or misdiagnosed. In addition to identifying low cerebrospinal fluid (CSF) hypocretin (orexin) levels, evaluation for narcolepsy requires in-laboratory polysomnography (PSG). Polysomnography is the gold standard for diagnosis of obstructive sleep apnea (OSA) as well as other sleep disorders. However, the use of home sleep apnea testing (HSAT) to screen for OSA in adults with EDS has increased greatly based on its lower cost, lower technical complexity, and greater convenience, versus PSG. The most commonly used, types 3 and 4, portable monitors for HSAT lack capability for electroencephalogram recording, which is necessary for the diagnosis of narcolepsy and other sleep disorders and is provided by PSG. These limitations, combined with the increased use of HSAT for evaluation of EDS, may further exacerbate the under-recognition of narcolepsy and other hypersomnias, either as primary or comorbid disorders with OSA. Adherence to expert consensus guidelines for use of HSAT is essential. Differential clinical characteristics of patients with narcolepsy and OSA may help guide correct diagnosis. Continued EDS in patients diagnosed and treated for OSA may indicate comorbid narcolepsy or another sleep disorder. Although HSAT may diagnose OSA in appropriately selected patients, it cannot rule out or diagnose narcolepsy. Therefore, at present, PSG and MSLT remain the cornerstone for narcolepsy diagnosis.