Objective
Depression symptom measures that include somatic symptoms may inflate severity estimates among medically ill patients, including patients with systemic sclerosis (SSc; scleroderma). The 9‐item Patient Health Questionnaire (PHQ‐9) is increasingly used to assess depressive symptoms in medical settings, but it is not known whether PHQ‐9 scores are influenced by somatic symptoms common in medical illness. The objective was to assess whether SSc patients had higher somatic symptom scores on the PHQ‐9 than non–medically ill respondents from the general population matched on cognitive/affective scores.
Methods
SSc patients from the Canadian Scleroderma Research Group Registry were matched with respondents from a random population survey of Alberta, Canada residents who were without chronic disease on total PHQ‐9 cognitive/affective scores (5 items), sex, and, as close as possible, age. PHQ‐9 somatic scores (4 items) were compared between SSc patients and healthy Alberta survey respondents using t‐tests for unadjusted analyses and analysis of covariance to adjust for age differences that remained after matching.
Results
Somatic symptoms accounted for 64% of the total PHQ‐9 scores for 762 matched SSc patients (n = 837 total) compared to 56% for 762 matched Alberta population survey respondents (n = 3,304 total), a mean difference of 1.0 point, or 19% of the total scores for the SSc patients (Hedges's g = 0.38). After adjusting for age, the mean difference increased to 1.4 points, reflecting 25% of the SSc patients' total scores (Hedges's g = 0.55).
Conclusion
PHQ‐9 scores among patients with SSc may include a small to moderate amount of variance from somatic symptoms that are not necessarily related to depression.