A 40-year-old man reports irresistible daytime sleepiness, cataplexy triggered by laughter, sleep paralysis, and hypnagogic hallucinations. PSG shows sleep-onset REM period (SOREMP) < 15 minutes on MSLT. The neurotransmitter deficiency central to the pathophysiology is:
- A Dopamine
- B Serotonin
- C Orexin (hypocretin) ✓
- D Adenosine
Explanation
Narcolepsy type 1 (with cataplexy) is caused by selective loss of orexin (hypocretin)-producing neurons in the lateral hypothalamus, most commonly through an autoimmune mechanism targeting these neurons. CSF orexin-1 levels are undetectable or very low (≤110 pg/mL). The tetrad of excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic/hypnopompic hallucinations constitutes the classic presentation. MSLT showing ≥2 sleep-onset REM periods and mean sleep latency ≤8 minutes confirms the diagnosis. Treatment: modafinil/sodium oxybate (GHB) for EDS; sodium oxybate/venlafaxine for cataplexy.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.