Idiopathic hypersomnia is distinguished from narcolepsy by the absence of cataplexy and what other feature?

• A. Presence of cataplexy
• B. Absence of cataplexy
• C. Absence of cataplexy and absence of clear REM sleep abnormalities
• D. Frequent naps

Answer: (C)

The key idea is how idiopathic hypersomnia and narcolepsy differ in two main features: the presence of cataplexy and REM-related abnormalities on sleep testing. Narcolepsy often includes cataplexy and shows REM sleep abnormalities, such as sleep-onset REM periods (SOREMPs) during the multiple sleep latency test. Idiopathic hypersomnia, on the other hand, lacks cataplexy and does not show clear REM sleep abnormalities on testing. So the statement that best distinguishes idiopathic hypersomnia is that there is both an absence of cataplexy and an absence of clear REM sleep abnormalities.

Choosing a option that mentions cataplexy alone would point toward narcolepsy, and mentioning frequent naps alone isn’t definitive, since both conditions can involve daytime sleepiness.