title: Evaluation of the 9-item Patient Health Questionnaire (PHQ-9) as an assessment instrument for symptoms of depression in patients with multiple sclerosis.
abstract: BACKGROUND
  Patients with multiple sclerosis (MS) have a high prevalence of depression, but there are concerns regarding assessment of possible depression status using rating scales, such as the 9-item Patient Health Questionnaire (PHQ-9). The idea has been proposed that PHQ-9 scores are contaminated by the MS symptoms of fatigue and impaired concentration, decreasing the validity of measurement.
  
  
  OBJECTIVE
  To determine the extent to which scores on the PHQ-9 are contaminated by patients reporting symptoms attributable to MS.
  
  
  METHODS
  Baseline PHQ-9 scores from an ongoing prospective cohort study of depression in patients with MS (N = 173) were compared with those of a general population sample (N = 3304). Depression prevalence estimates for the MS and general population samples were calculated using conventional algorithm and cutoff point scoring methods, as well as modified scoring methods, excluding fatigue and concentration deficits. Correlations between scores on adjusted scoring methods were analyzed. The proportion that each item contributed to total PHQ-9 scores was also calculated. A logistic regression model evaluated the relationship between symptom severity and MS status corrected for age, sex, and other depressive symptoms.
  
  
  RESULTS
  Conventional PHQ-9 algorithm and cutoff point scoring yielded 2-week prevalence estimates of 9.8% and 21.4%, respectively, in patients with MS, and 3.3% and 8.4%, respectively, in the general population. In both samples, conventional and modified scoring methods were strongly correlated (Spearman rank correlation coefficient > 0.9). The proportion of total scores contributed by fatigue and concentration items was not different between samples. With adjustment for other depressive symptoms, the MS sample had greater odds of endorsement for guilt (odds ratio, 2.17; P = 0.025) and fatigue (odds ratio, 1.51; P = 0.046).
  
  
  CONCLUSIONS
  Inclusion or exclusion of fatigue and concentration items on the PHQ-9 scale does not substantially alter the performance of the scale. With use of the PHQ-9 in MS populations, we find no evidence to suggest that modified approaches to scoring are necessary.
authors.affiliation: University of Calgary, Calgary, Alberta, Canada.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Sjonnesen
authors.forename: Sandy
authors.initials: S
authors.lastname: Berzins
authors.forename: Kirsten M
authors.initials: KM
authors.lastname: Fiest
authors.forename: Andrew G
authors.initials: AG
authors.lastname: M Bulloch
authors.forename: Luanne M
authors.initials: LM
authors.lastname: Metz
authors.forename: Brett D
authors.initials: BD
authors.lastname: Thombs
authors.forename: Scott B
authors.initials: SB
authors.lastname: Patten
mesh_terms: D000465:Algorithms; D015897:Comorbidity; D003863:Depression / Q000175:diagnosis* / Q000453:epidemiology*; D003866:Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology; D006801:Humans; D016015:Logistic Models; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000523:psychology; D011569:Psychiatric Status Rating Scales; D011795:Surveys and Questionnaires