The Polish multicenter Treatment Resistant Depression Project (TRES-DEP) has aimed to study a number of demographic, clinical and psychometric characteristics comparing patients with treatment-resistant (TR) and treatment non-resistant depression (TNR). Fifty patients with TR depression (group 1) and 50 patients with TNR depression (group 2) were included in this preliminary analysis.

Treatment-resistant depression was recognized on account of lack of significant improvement following at least two adequate courses of antidepressant treatment. The exclusion criteria were treatment with mood stabilizers, diagnosis of substance misuse, dementia or severe somatic disease. The presence of bipolarity features was assessed by Polish version of Mood Disorder Questionnaire (MDQ).

Significantly more patients with TR depression compared with TNR had family history of mental disorders, especially alcohol dependence (24% vs 8%, p=0,03), had more previous depressive episodes (8.5±5.0 vs 5.1±3.8; p=0.001), and reported shorter time from the last hospitalization (14.8±26.5 vs 41.9±71.1 months, p< 0.005). Patients from group 1 significantly more frequently fulfilled MDQ criteria for bipolarity than patients from group 2 (44% vs 12%, p< 0.001). Among TR patients, MDQ-positive compared with MDQ-negative more frequently reported treatment nonadherence (41% vs 18%, p=0.055), suicidal attempts (41% vs 18%, p=0.055) and inadequate remission (100% vs 21%; p< 0.05).

Our preliminary results point to clinical differences between patients with TR and TNR depression, including higher scores on bipolarity scale in TR. The features of bipolarity may be an important reason for non-response during antidepressant treatment of depression and worse clinical course and outcome.