Somatic symptoms of depression are unlikely to be biased by multiple sclerosis (MS) symptoms, according to a recent study. However, the use of certain somatic symptoms to assess anxiety may be biased for those with high MS symptoms. People with MS (n=513) completed a survey about MS symptoms, treatments, and distress. The Patient Health Questionnaire-9 assessed depression, and the patient-report version of the Primary Care Evaluation of Mental Disorders assessed anxiety. Participants were grouped into low vs high MS symptoms based on self-reported symptoms and as high vs low disability by the Expanded Disability Status Scale (EDSS). Groups were compared using differential item functioning analysis. Researchers found:

• No bias was found on somatic symptoms of depression comparing high vs low MS symptom groups or comparing groups based on EDSS scores.
• 2 anxiety symptoms (fatigue and muscle tension) showed bias comparing high vs low MS symptom groups and comparing high vs low groups based on EDSS scores.
• Intraclass correlations suggested a small effect due to bias in the somatic symptoms of anxiety.