title: High rates of depressive symptoms among patients with systemic sclerosis are not explained by differential reporting of somatic symptoms.
abstract: OBJECTIVE
  Between 36% and 65% of patients with systemic sclerosis (SSc) report symptoms of depression above cutoff thresholds on self-report questionnaires. The objective of this study was to assess whether these high rates result from differential reporting of somatic symptoms related to the high physical burden of SSc.
  
  
  METHODS
  Symptom profiles reported on the Center for Epidemiologic Studies Depression Scale (CES-D) were compared between a multicenter sample of 403 patients with SSc and a sample of respondents to an Internet depression survey, matched on total CES-D score, age, race/ethnicity, and sex. An exact nonparametric generalized Mantel-Haenszel procedure was used to identify differential item functioning between groups.
  
  
  RESULTS
  Patients with SSc reported significantly higher frequencies (moderate to large effect size; P < 0.01) on 4 CES-D somatic symptom items: bothered, appetite, effort, and sleep. Internet respondents had higher item scores on 2 items that assessed interpersonal difficulties (unfriendly, large effect size; P < 0.01; disliked, large effect size; P < 0.01) and on 2 items that assessed lack of positive effect (happy, moderate effect size; P = 0.01; enjoy, large effect size; P < 0.01). Adjustment of standard CES-D cutoff criteria for potential bias due to somatic symptom reporting resulted in a reduction of only 3.6% in the number of SSc patients with significant symptoms of depression.
  
  
  CONCLUSIONS
  High rates of depressive symptoms in SSc are not due to bias related to the report of somatic symptoms. The pattern of differential item functioning between the SSc and Internet groups, however, suggests some qualitative differences in depressive symptom presentation.
authors.affiliation: Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada. brett.thombs@mcgill.ca
authors.forename: Brett D
authors.initials: BD
authors.lastname: Thombs
authors.forename: Samantha
authors.initials: S
authors.lastname: Fuss
authors.forename: Marie
authors.initials: M
authors.lastname: Hudson
authors.forename: Orit
authors.initials: O
authors.lastname: Schieir
authors.forename: Suzanne S
authors.initials: SS
authors.lastname: Taillefer
authors.forename: Joshua
authors.initials: J
authors.lastname: Fogel
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Ford
authors.forename: Murray
authors.initials: M
authors.lastname: Baron
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003863:Depression / Q000150:complications* / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D012595:Scleroderma, Systemic / Q000150:complications / Q000523:psychology*; D012647:Self-Assessment; D012720:Severity of Illness Index