Objective: To study concordance between self-report measures and clinical observations of functional disability in ankylosing spondylitis (AS), rheumatoid arthritis (RA), and fibromyalgia (FM).
Methods: 35 patients with AS completed 9 selected items of the Functional Index questionnaire, whereas 12 patients with RA and 13 with FM completed 7 selected items of the Arthritis Impact Measurement Scales. Five days later, all 60 patients and 4 controls actually performed the selected activities, which were recorded on video. The tapes were assessed in random order by 12 observers (6 occupational therapists and 6 physicians). Both patients and observers indicated functional disability on a 10 cm visual analog scale (VAS).
Results: Interobserver agreement was high (Cronbach's alpha 0.98). All observers scored the 4 healthy controls as having no disability at all. Mean discordance scores (VAS patients minus VAS observers) for the selected items were negligible in AS [-0.17 cm (p = 0.30)], moderate in RA [+1.10 cm (p = 0.06)] and high in FM [+2.44 cm (p < 0.01)].
Conclusion: Discordance between self-report questionnaires and observed functional disability is a feature most striking in FM. In validation of self-report questionnaires of functional disability the appropriate spectrum of rheumatological diagnoses should be considered.