A 25-year-old man reports sudden episodes of muscle weakness triggered by laughter or excitement, excessive daytime sleepiness despite 8 hours of night sleep, and hypnagogic hallucinations. Sleep-onset REM periods (SOREMPs) are found on multiple sleep latency test (MSLT). What is the DIAGNOSIS and underlying neurochemical deficiency?

• A Idiopathic hypersomnia; serotonin deficiency
• B REM sleep behavior disorder; dopamine deficiency
• C Narcolepsy type 1; orexin (hypocretin) deficiency ✓
• D Kleine-Levin syndrome; histamine deficiency

Explanation

Narcolepsy type 1 (with cataplexy) is characterized by the tetrad of excessive daytime sleepiness, cataplexy (brief sudden loss of muscle tone triggered by strong emotions), sleep paralysis, and hypnagogic/hypnopompic hallucinations. The MSLT shows ≥2 SOREMPs and mean sleep latency ≤8 minutes. It is caused by destruction of hypocretin (orexin)-producing neurons in the lateral hypothalamus (likely autoimmune), resulting in CSF orexin levels <110 pg/mL. Treatment includes sodium oxybate for cataplexy, modafinil/armodafinil for sleepiness, and stimulants.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.