Somatic symptoms have negligible impact on Patient Health Questionnaire-9 depression scale scores in neurological patients

Irene L. Katzan, Brittany Lapin*, Sandra Griffith, Lara Jehi, Hubert Fernandez, Erik Pioro, Stewart Tepper, Paul K. Crane

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Background and purpose: There is concern that the Patient Health Questionnaire-9 (PHQ-9) depression scale may be impacted by the presence of somatic symptoms (differential item functioning [DIF]) in patients with neurological conditions. We evaluated the PHQ-9 for the presence and impact of DIF in large clinical samples of neurological patients. Methods: We conducted a cross-sectional study of patients seen at the Cleveland Clinic Cerebrovascular, Headache, Movement Disorder, and Neuromuscular clinics who completed the PHQ-9 and patient-reported disease severity measures as part of standard care between 29 July 2008 and 21 February 2013. We evaluated PHQ-9 items for DIF with respect to disease-specific severity for each condition. Salient DIF impact was characterized as a difference between DIF-adjusted and unadjusted PHQ-9 scores. Results: Included in the study were 2112 patients with stroke, 8221 with migraine, 440 with amyotrophic lateral sclerosis (ALS), and 5022 with Parkinson disease (PD). Several PHQ-9 items demonstrated DIF with respect to disease-specific severity, although salient DIF was present in very few patients (stroke, n = 0; migraine, n = 1; ALS, n = 13; PD, n = 1). Conclusions: PHQ-9 items function consistently across disease severity, with salient levels of DIF impact found only for a very small proportion of people. These results suggest that the PHQ-9 provides a consistent measure of depression severity among people with neurological conditions associated with somatic symptoms that overlap with depression.

Original languageEnglish (US)
Pages (from-to)1812-1819
Number of pages8
JournalEuropean Journal of Neurology
Issue number6
StatePublished - Jun 2021
Externally publishedYes


  • depression
  • neurological disorders
  • psychometrics
  • screening

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology


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