BACKGROUND: A population-based method for estimating disease burden is commonly used. Nevertheless, these measurements do not entirely capture the comprehensive burden of illness on an individual patient. To address the problem, the Individual Burden of Illness Index (IBI index) Index was created and validated, specifically for major depressive disorder. The IBI represents the overall influence of the condition, encompassing distress from symptom intensity, functional impairment, and the patient's quality of life.

AIM: The aim of the study was to approve and validate the IBI index for the integral assessment of disease burden in patients with bipolar disorder (BD) in remission.

METHODS: The cross-sectional study was conducted in the outpatient psychiatric services in Saint Petersburg, Russia, from April through October 2020. Eighty-five patients aged 18 to 45 (mean age 36.6±5.7 years) with BD (type I - 75%, n=64; type II - 25%, n=21) in remission were examined. The study procedure included a structured clinical interview and the use of clinical scales: the World Health Organization's Quality of Life Questionnaire, Hamilton Rating Scale for Depression (HDRS), Young Mania Rating Scale (YMRS), and Personal and the Social Performance Scale.

RESULTS: The principal component analysis in accordance with the adjusted one showed that the burden of illness in patients with BD in remission is directly related to the severity of residual depressive symptoms, reflected in the HDRS score: as the HDRS score increases (0.27, p <0.001), residual mania (-0.14, p <0.001), social functioning (-0.06, p <0.001), and quality of life (-0.04, p <0.001) decrease. In contrast, when there are remaining residual mania symptoms, as indicated by the YMRS score, the result tends to be a lower burden, better social functioning, and enhanced quality of life.

CONCLUSION: The study has demonstrated through statistical means a successful adaptation and validation of the previously calculated IBI index for patients with BD in remission. Residual affective symptoms were shown to have different impacts on the social functioning of patients with BD in remission, indicating the need for a timely assessment and targeted therapy of these symptoms in such patients.