REM Density, Leg Movements, and REM Sleep without Atonia: Differentiating Type 1 from Type 2 Narcolepsy Through Polysomnographic Analysis, a Preliminary Study.

Objective: This study aimed to identify distinct REM sleep characteristics that differentiate type 1 narcolepsy (NT1) from type 2 narcolepsy (NT2) using polysomnography (PSG), while acknowledging the need for future validation against other hypersomnia disorders.

Methods: A retrospective review included 31 patients with NT1, 21 patients with NT2, and 24 healthy participants. Each participant underwent overnight PSG and a subsequent multiple sleep latency test (MSLT) to assess REM sleep parameters including average REM density, neck myoclonus index, and leg movement index. Cerebrospinal fluid (CSF) samples were collected to measure orexin-A and catecholamine levels.

Results: 1. NT1 patients demonstrated significantly higher average REM density versus NT2 (P<0.05); 2. Elevated REM sleep characteristics in NT1: neck myoclonus index (0.82 vs 0.25 n/hr), leg movement index (18 vs 7 n/hr), and REM sleep without atonia (RSWA) incidence (71% vs 24%) (all P<0.05); 3. Biochemical correlations: REM density negatively correlated with orexin-A (r=-0.42) and positively with norepinephrine (r=0.38) (both P<0.05).

Conclusion: While REM density, leg movement index and RSWA show promise for NT1/NT2 differentiation, these findings require validation in cohorts including idiopathic hypersomnia and other central hypersomnolence disorders. The observed electrophysiological patterns may reflect orexin-mediated dysregulation of REM motor control, but their diagnostic specificity remains to be established.