Inconsistent Use of “Not Better Explained” Criterion Raises Questions in Sleep Disorder Diagnosis

A new systematic review is drawing attention to inconsistencies in how a critical diagnostic rule is applied across major sleep disorder classification systems, with potential implications for diagnostic accuracy and patient care.¹

Researchers of the study, published in Journal of Sleep Research, say their findings highlight the need for consistent use of the “Not Better Explained” (NBE) exclusion criterion, which plays a central role in clinical diagnosis by ensuring that symptoms attributed to a sleep disorder are not better explained by another sleep-related issue or by a different condition, such as a medical illness or neurological or psychiatric disorder.² In practice, the criterion acts as a safeguard against misdiagnosis and overmedicalization, helping clinicians draw clearer boundaries between normal variations in sleep and true pathology.

Despite its importance, the study found notable differences in how consistently and clearly the NBE criterion is applied across 2 widely adopted diagnostic frameworks: 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).

“As sleep medicine continues to evolve at the intersection of multiple disciplines, a more precise and transparent use of diagnostic criteria (especially those like ‘not better explained’—the NBE criterion that requires expert judgment) will be essential for aligning clinical effectiveness and epistemological precision,” wrote the researchers.

The group conducted a systematic content analysis of 10 major sleep disorders, including insomnia, narcolepsy, sleep apnea, circadian rhythm disorders, and parasomnias. They evaluated whether the NBE criterion was present, how it was worded, and which alternative conditions were explicitly excluded.

The results revealed that ICSD-3-TR includes the NBE criterion more frequently, appearing in 9 of the 10 disorders analyzed, compared with 7 of 10 in the DSM-5-TR. Overall, there was strong overlap between the 2 systems, with a similarity score (Jaccard index) of 0.75. However, the differences that did emerge were meaningful and largely centered on how the criterion is framed and applied.

One of the most striking distinctions was in the types of conditions excluded. The ICSD-3-TR more often excludes other sleep disorders, substance use, and sleep-related behaviors, reflecting a framework rooted within sleep medicine itself. By contrast, the DSM-5-TR places greater emphasis on excluding medical and mental health conditions, aligning more closely with its broader psychiatric orientation.

These differences reflect deeper philosophical approaches to diagnosis, explained the researchers, noting that ICSD-3-TR tends to focus on differentiating between sleep disorders, while the DSM-5-TR emphasizes distinguishing sleep conditions from broader medical or psychiatric causes. This divergence can influence how clinicians interpret symptoms, particularly in patients with multiple overlapping conditions.

The study also highlighted variability in the wording of the NBE criterion. The ICSD-3-TR used more standardized language, most commonly the phrase “not better explained,” across disorders. In contrast, the DSM-5-TR employs a wider range of expressions, including “not attributable to,” “not adequately explained,” and “does not occur exclusively,” which may introduce ambiguity in clinical interpretation, wrote the researchers.

This lack of consistency could have practical consequences, flagged the group. Variability in how exclusion criteria are phrased and applied may contribute to differences in diagnosis rates, comorbidity assessments, and treatment decisions. For example, in insomnia, the DSM-5-TR explicitly considers whether symptoms may be better explained by mental health conditions, while the ICSD-3-TR takes a more permissive approach that allows insomnia to be diagnosed alongside comorbid disorders.

The implications extend across multiple conditions. In circadian rhythm sleep–wake disorders, the ICSD-3-TR included exclusion criteria addressing medical and substance-related causes, whereas the DSM-5-TR did not include an NBE clause, raising concerns about potential overdiagnosis. Meanwhile, in sleep apnea, both systems largely omit the NBE criterion, reflecting reliance on objective physiological markers rather than differential diagnostic logic.

Based on their findings, the researchers called for greater harmonization in future revisions of diagnostic classifications, including more consistent wording and clearer guidance on how to apply exclusion criteria in the context of comorbid conditions. Incorporating both intra-disciplinary (sleep-specific) and interdisciplinary (medical and psychiatric) perspectives may help strike a balance between diagnostic precision and clinical practicality.

References

1. Micoulaud-Franchi J-A, Martin VP, Coelho J, et al. Investigation of the “not better explained” diagnosis criteria in sleep disorder classifications: A systematic content analysis and critical review. J Sleep Res. Published online March 13, 2026. doi:10.1111/jsr.70327

2. Stores G. Clinical diagnosis and misdiagnosis of sleep disorders. J Neurol Neurosurg Psychiatry. 2007;78(12):1293-1297. doi:10.1136/jnnp.2006.111179