title: Influence of somatic symptoms on Patient Health Questionnaire-9 depression scores among patients with systemic sclerosis compared to a healthy general population sample.
abstract: 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: McGill University and Jewish General Hospital, Montreal, Quebec, Canada.
authors.forename: Allison
authors.initials: A
authors.lastname: Leavens
authors.forename: Scott B
authors.initials: SB
authors.lastname: Patten
authors.forename: Marie
authors.initials: M
authors.lastname: Hudson
authors.forename: Murray
authors.initials: M
authors.lastname: Baron
authors.forename: Brett D
authors.initials: BD
authors.lastname: Thombs
mesh_terms: D000328:Adult; D000368:Aged; D000416:Alberta / Q000453:epidemiology; D003863:Depression / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D005260:Female; D006306:Health Surveys / Q000379:methods* / Q000592:standards; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods*; D012042:Registries; D012595:Scleroderma, Systemic / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D012720:Severity of Illness Index; D013001:Somatoform Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D011795:Surveys and Questionnaires