Background Functional ability, which includes the ability to perform activities of daily living (ADL), is considered a core outcome domain in rheumatology. Recommendations for assessing ADL ability include the use of generic and diseases-specific questionnaires based on self-report and one of the most frequently used instruments is the Health Assessment Questionnaire Disability Index (HAQ-DI). Self-report reflects the person's perception of extent of disability, which may be influenced by pain and other psychosocial factors. A poor agreement between self-reported and observed ADL ability has previously been demonstrated in rheumatic populations based on other self-report instruments.

Objectives to evaluate relationships between HAQ-DI scores and measures of observed ADL ability in patients with inflammatory and non-inflammatory rheumatic diseases and the association between pain and fatigue and these disability measures.

Methods patients with rheumatoid arthritis (RA), knee osteoarthritis (OA) and fibromyalgia (FM) were assessed with the HAQ-DI. The Assessment of Motor and Process Skills (AMPS) was used to obtain measures of observed ADL ability. Two domains of observed ADL ability were evaluated: ADL motor skills (moving self and objects) and ADL process skills (organizing and adapting actions). Pain and fatigue were assessed by 100mm visual analogue scales (VAS). The project was approved by the local ethical committee (H-B-2007–084).

Results 143 women (50 with RA, 27 with knee OA, 66 with FM), mean age 51.2 (11.8) participated. Baseline characteristics and correlations are presented in table 1. Patients with FM had the highest pain, fatigue, and HAQ disability scores and the poorest performance on the AMPS. The relationships between self-reported and observed ADL motor ability were weak to moderate across all diagnostic groups; strongest in patients with knee OA. Relationships with the AMPS ADL process ability measure were weak to insignificant. Level of pain, and not fatigue, showed the strongest relationship with self-reported functional ability across all diagnostic groups. A weak to moderate relationship between pain and AMPS ADL motor ability measures were also present in patients with RA and OA, but insignificant in patients with FM (r= -0.16, p=0.195).

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Conclusions the relation between self-reported and observed functional ability is low across a spectrum of musculoskeletal diagnoses, even when using instruments recommended for these populations including the HAQ-DI. This has major implications on how to interpret and measure functional ability in the future as both methods should probably accompany each other. Interestingly pain was not associated with observed motor ADL ability in FM as opposed to RA and OA.

Disclosure of Interest None declared