Diagnostic Conversion From Psychotic Unipolar Depression to Bipolar and Psychotic Disorders: A Swedish Registry-Based...

To estimate the cumulative incidence of diagnostic conversion from psychotic unipolar depression to bipolar and psychotic disorders in Sweden.

Data from Swedish national registers were used to identify incident cases of psychotic unipolar depression between 2005 and 2011. To minimize the risk of misclassification, patients with a prior history of psychotic disorders, bipolar disorders, or manic episodes were excluded. Patients were followed until the first occurrence of a diagnostic change, death, or December 31, 2021. The cumulative incidence of diagnostic change was estimated using a competing risk model.

A total of 7836 patients diagnosed with psychotic depression between 2005 and 2011 were included. The median age at index diagnosis of psychotic depression was 49 years (interquartile range: 35-65), and 56.7% were women. By the end of follow-up, 28.8% (95% CI: 27.7-29.9) of patients had undergone a diagnostic change to either a psychotic or bipolar disorder. The cumulative incidence of conversion was higher to psychotic disorders (17.5%, 95% CI: 16.6-18.4) than to bipolar disorders (14.7%, 95% CI: 13.8-15.5). In a sensitivity analysis requiring at least two recorded diagnoses separated by ≥ 1 year, the overall incidence of diagnostic change decreased to 19.0% (95% CI: 18.1-20.0), with corresponding rates of 10.0% (95% CI: 9.3-10.7) to psychotic disorders and 9.8% (95% CI: 9.1-10.5) to bipolar disorders. Diagnostic conversion was more common among younger individuals.

Approximately 20%-30% of patients diagnosed with psychotic depression in secondary care in Sweden are expected to receive a subsequent diagnosis of a bipolar or psychotic disorder within 17 years. This has important clinical implications, as prognosis and treatment strategies differ between these conditions. Further research is needed to identify risk factors for diagnostic conversion to improve early detection and management.