RESUMEN
Objectives: The bipolar spectrum concept has resulted in a paradigm shift that has affected both the diagnosis and therapy of mood disorders, with bipolarity becoming an indicator of treatment resistance in depression. Evening circadian preference has also been linked to affective disorders. The aim of our study was to confirm the relationship between the severity of depressive symptoms, bipolar features, chronotype, and sleep quality among patients with major depressive disorder. Methods: A group of 55 individuals who were recruited from a mental health outpatient clinic completed the following psychometric tools: a Chronotype Questionnaire comprising morningness-eveningness (ME) and subjective amplitude of the rhythm (AM) scales, the Hypomania Checklist 32 (HCL-32), the Beck Depression Inventory (BDI) and the Pittsburgh Sleep Quality Index (PSQI). Results: Factor analysis identified two latent components, accounting cumulatively for 58% of variables: depressive symptoms (BDI and PSQI) and bipolarity (ME, AM, and HCL-32). After rotation, ME loading in the first factor increased the result to a significant level. The correlation between the two components was very low. Conclusions: Evening chronotype appears to be a bipolarity-related marker, with this relationship being independent of its link to depressive symptoms and sleep quality. Eveningness and high circadian rhythm amplitude may offer promise as diagnostic, prognostic, and therapeutic predictors.