Diagnostic conversions from major depressive disorder into bipolar disorder in an outpatient setting: results of a retrospective chart review

Background: The aim of the study was to check the stability of a diagnosis of major depressive disorder (MDD) in an outpatient setting, as well as to assess the scope of diagnostic conversions into bipolar disorder (BD).

Methods: Retrospective chart review of 122 patients with a primary diagnosis of MDD.

Results: Diagnostic conversion from MDD into BD was noticed in 40 subjects (32.8%), 25 patients (20.5%) were treatment-resistant. Mean time to the conversion was 9.27±8.64 years. A negative correlation between the age of illness onset and time to diagnostic conversion was observed (-0.41; p<0.05). Earlier onset of MDD was associated with higher risk of diagnostic conversion (<30vs≥30 years of age at onset: 69% vs 28%, p=0.0001; <35vs≥35 years of age: 50% vs 25%, p=0.0065). Treatment-resistance was more prevalent in the BD conversion group (40% vs 11%; p=0.0002). Diagnostic conversion into BD was also related longer duration of treatment received, higher number of illness episodes, and higher number of hospitalizations.

Limitations: Retrospective design of the study.

Conclusions: The problem of diagnosis evolution from MDD to BD was observed in about 1/3 of patients, and was associated with treatment-resistance of depression, earlier onset of depression, longer time of treatment, higher number of depressive episodes and hospitalizations. The variables above may be a useful predictor of bipolar diathesis.