Objective: The reported rates of depressive symptoms in patients with SSc are high. The Center for Epidemiologic Studies Depression Scale (CES-D) is the only measure of depressive symptoms validated for SSc patients. The objective of this study was to assess the internal consistency reliability, convergent validity and strength of association with clinical correlates of the 9-item version of the Patient Health Questionnaire depression scale (PHQ-9) compared with the CES-D in SSc.
Methods: We conducted a cross-sectional, multicentre study of 566 SSc patients who were assessed with the PHQ-9 and CES-D scales, and through clinical histories and medical examinations. Internal consistency reliability was assessed with Cronbach's alpha, convergent validity with Pearson's correlation and the relationship of socio-demographic and clinical variables with the PHQ-9 and CES-D scores using multiple linear regression.
Results: Scale reliability was good for the PHQ-9 (alpha = 0.87) and similar to the CES-D (alpha = 0.90). Correlations of the PHQ-9 total score were -0.68 with mental health, -0.43 with physical health, 0.44 with disability, 0.40 with pain and 0.79 with fatigue, which were all in the expected direction and similar to the results with the CES-D. Regression coefficients of clinical correlates did not differ significantly between models using the PHQ-9 and CES-D.
Conclusion: The PHQ-9 is reliable and valid for use as a measure of depressive symptom severity in patients with SSc and performs similarly to the CES-D. However, the PHQ-9 is advantageous because it is half the length of the CES-D, easily administered and scored, and is increasingly used across many patient groups for assessment in research and clinical settings.