The Patient Health Questionnaire (PHQ-9) as a tool to screen for depression in people with multiple sclerosis: a cross-sectional validation study

Background: Depression has a point prevalence of 25% and lifetime prevalence of 50% in people with multiple sclerosis (pwMS). Due to accessibility and brevity, the 9-item Patient Health Questionnaire (PHQ-9) may be a useful tool in clinical practice for screening and monitoring of depressive symptoms in people with MS (pwMS). Methods: The objective of this study was to evaluate the reliability, validity and acceptability of the PHQ-9 as a screening tool for depressive symptoms in pwMS. PwMS completed online questionnaires at 3 time-points over 4-weeks. The PHQ-9, Multiple Sclerosis Impact Scale (MSIS-29), Centre for Disease Control Health-Related Quality of Life Measure (CDC-HQOL-4) and clinical history. Results: 103 participants completed the PHQ-9 at three time points, 43% were categorised as depressed on at least one response. The PHQ-9 exhibited high internal reliability (Cronbach's alpha = 0.89), and test-re-test agreement (ICC 0.89, 95% CI 0.85-0.91). Convergent validity was indicated through positive correlation with the mental health items on the MSIS-29 (r = 0.46 and r = 0.50) and CDC-HQOL-4 (r = 0.79 and r = 0.73) at both assessment points. Positive correlations between the PHQ-9 and the MSIS-29 (r = 0.86 and r = 0.84) and CDC-HQOL-4 (r = 0.55 and r = 0.37) physical symptom sub-scores did not indicate divergent validity. 93% of ratings evaluated the PHQ-9 as "Very" or "Completely" acceptable. Conclusion: The PHQ-9 is a reliable and valid measure of depressive symptoms in people with MS. Given its accessibility, ease of administration, and acceptability, we recommend the PHQ-9 as a tool to screen for depressive symptoms in people with MS.