A New Electrophysiological Approach to Sleep Microstructure: The Gülhane Classification of K-Complex Subtypes in Narcolepsy Type 1 and Type 2

Study Objectives: While the pathophysiology of Narcolepsy Type 1 (NT1) involves hypocretin deficiency, the microstructural electrophysiological features that distinguish NT1 from Narcolepsy Type 2 (NT2) remain incompletely defined. This study evaluated sleep microstructure with a six-subtype K-complex (KC) categorization (Gülhane Classification). Methods: Retrospective polysomnography from the December 2016–January 2026 clinical archive was reviewed. K-complex scoring defined the analyzed sample: NT1 n = 18, NT2 n = 13, and simple-snoring controls with AHI < 5 (n = 15). Complete overnight PSG summaries were available for NT1 n = 16 and NT2 n = 13. Six visually defined KC subtypes (Isolated-KC, KC-Burst, KC-Sigma, KC-Delta, Polyphasic-KC, and Polyphasic-KC-Sigma) were compared across Descendant, Intermediate, and Ascendant portions of the NREM cycle. Results: Compared with controls, NT1 showed lower Isolated-KC and KC-Sigma counts across cycle periods (p < 0.05). NT1 also had higher wake after sleep onset (WASO; 34.7 ± 21.1 min) and lower sleep efficiency (90.7 ± 5.4%) than NT2. NT1–NT2 differences that reached p < 0.05 were KC-Delta in the Intermediate (p = 0.015) and Descendant (p = 0.030) periods, Isolated-KC in the Intermediate period (p = 0.039), and KC-Sigma in the Descendant period (p = 0.041). Conclusions: In this retrospective cohort, morphological KC subtyping showed a coherent reduction in Isolated-KC and KC-Sigma in NT1. The findings are descriptive and require prospective validation; they do not constitute a standalone diagnostic test.