Investigation of the “Not Better Explained” Diagnosis Criteria in Sleep Disorder Classifications: A Systematic Content Analysis and Critical Review

Accurate diagnostic boundaries between normal and pathological sleep are essential for appropriate care. Among diagnostic criteria, the "Not Better Explained" (NBE) exclusion criterion prevents misclassification by ensuring that symptoms are not attributable to another disorder. Despite its importance, the NBE criterion has never been systematically analysed across the International Classification of Sleep Disorders-Third Edition Text Revision (ICSD-3-TR) and the Diagnostic and Statistical Manual of Mental Disorders-Fifth Edition Text Revision (DSM-5-TR). A systematic content analysis was conducted using a validated methodology for diagnostic criteria evaluation. Ten major sleep disorders were selected based on prevalence and clinical relevance. For each disorder in both classifications, NBE formulations were identified, extracted, and categorised by excluded condition and causal wording. The Jaccard index quantified overlap, and visualisations compared exclusion patterns. The ICSD-3-TR included the NBE criterion in 9 of 10 disorders, whereas the DSM-5-TR included it in 7 of 10. Overall overlap was strong (Jaccard index = 0.75). Differences were mainly semantic. The ICSD-3-TR more often excluded "sleep disorders," "substance use," and "sleep behaviours," while the DSM-5-TR emphasised "medical" and "mental disorders." The ICSD-3-TR predominantly used "not better explained," whereas the DSM-5-TR employed more variable formulations ("not attributable," "not adequately explained"…). By highlighting the strengths and inconsistencies in the use of the NBE criterion, we aim to contribute to a more empirically and conceptually grounded framework for sleep disorder diagnosis. Our work aims to inform ongoing efforts to improve the reliability, validity, and clinical utility of diagnostic classifications in sleep medicine.