What are the key diagnostic criteria for narcolepsy in adults, and how can I differentiate it from other sleep disorders?

Key diagnostic criteria for narcolepsy in adults include excessive daytime sleepiness that is persistent and not explained by other causes, often accompanied by cataplexy (sudden loss of muscle tone triggered by emotions), hypnagogic hallucinations, sleep paralysis, and disrupted nocturnal sleep. Diagnosis is primarily clinical but supported by objective testing such as polysomnography followed by a multiple sleep latency test (MSLT) demonstrating a mean sleep latency of ≤8 minutes and two or more sleep-onset rapid eye movement periods (SOREMPs) during the MSLT. Cerebrospinal fluid hypocretin-1 measurement may also aid diagnosis in uncertain cases Dyken & Yamada 2005Chavda et al. 2022.

Differentiation from other sleep disorders is critical, especially from obstructive sleep apnoea/hypopnoea syndrome (OSAHS), which can also cause excessive daytime sleepiness but is characterized by disrupted breathing during sleep, snoring, witnessed apnoeas, and often obesity or comorbidities such as hypertension or diabetes. OSAHS diagnosis relies on sleep studies showing apnoeas/hypopnoeas and oxygen desaturation, whereas narcolepsy shows characteristic REM abnormalities and sleep onset patterns without respiratory events NICE NG202. The presence of cataplexy is a key clinical feature distinguishing narcolepsy from OSAHS and other hypersomnias Miano et al. 2024.

In clinical practice, a detailed sleep history focusing on symptoms such as cataplexy, sleep paralysis, and hallucinations, combined with sleep study results, helps differentiate narcolepsy from other causes of excessive sleepiness. Use of assessment tools like the Epworth Sleepiness Scale can quantify sleepiness but cannot alone differentiate narcolepsy from other disorders NICE NG202. Polysomnography and MSLT remain the gold standard for diagnosis, with hypocretin testing reserved for complex cases Dyken & Yamada 2005Chavda et al. 2022Miano et al. 2024.