Idiopathic hypersomnia differs from narcolepsy in that it lacks which features?

• A. It includes cataplexy
• B. It has REM sleep abnormalities
• C. It is characterized by excessive daytime sleepiness without cataplexy and without clear REM abnormalities
• D. It is defined by frequent naps

Answer: (C)

The main idea is that narcolepsy typically includes two big features: cataplexy (sudden loss of muscle tone) and abnormal REM sleep patterns on testing. Idiopathic hypersomnia, however, shows excessive daytime sleepiness without cataplexy and without clear REM abnormalities. So the best description is that idiopathic hypersomnia is characterized by daytime sleepiness without cataplexy and without clear REM abnormalities, which is exactly what differentiates it from narcolepsy. Frequent naps can occur in various sleep disorders and aren’t the defining distinction here.