Nightmare disorder and depression: Exploring a neglected clinical association

Nightmares are overrepresented in psychiatric disorders and are strongly associated with suicidality, especially in Major Depressive Episode (MDE). This study had two main objectives: (1) to determine an optimal diagnostic cutoff for the Nightmare Severity Index (NSI) to identify Nightmare Disorder (ND), and (2) to compare the clinical profiles of MDE patients with ND (MDE-ND) and without ND (MDE-WND). We hypothesized that MDE-ND represents a more severe depressive subtype. This prospective case-control study was conducted in routine clinical settings. Participants were adults diagnosed with MDE according to DSM-5 criteria. Two groups were defined using NSI scores. The NSI cutoff score for diagnosing ND was determined using a Receiver Operating Characteristic (ROC) curve and the Youden Index. Psychiatric symptoms, sleep quality, and circadian rhythms were assessed using self-report questionnaires. Objective sleep and circadian rhythm parameters were measured using actigraphy. The NSI demonstrated excellent diagnostic performance with a cutoff ≥10 (sensitivity:96.67%, specificity:93.94%). Nearly half (49.6%) of MDE patients met ND criteria. Compared to MDE-WND, MDE-ND patients showed greater clinical severity, including higher lifetime and current suicidality and more severe depressive, anxiety, and insomnia symptoms. Objectively, they exhibited longer sleep latency, poorer sleep continuity, and lower sleep efficiency. Logistic regression identified anxiety severity, insomnia, and female gender as significant factors associated with ND. Mediation analyses revealed indirect associations within the tested models between nightmares and suicidality with anxiety mediating the link. MDE-ND is a more severe depressive subtype, with greater psychiatric burden and sleep disturbances. Early identification may help reduce suicidality by targeting nightmares in this high-risk group.