Functional impairment measurement in psoriatic arthritis: Importance and challenges

Patients with psoriatic arthritis (PsA) experience substantial physical impairment. This is commonly assessed using the patient-reported Health Assessment Questionnaire-Disability Index (HAQ-DI), which was originally developed in rheumatoid arthritis. The purpose of this review is to examine the value and challenges of using the HAQ-DI in patients with PsA, and to discuss alternative measures of functional impairment in this condition.

A literature search was performed in the MEDLINE, BIOSIS Previews, Embase, Derwent Drug File, and SciSearch databases using relevant terms and key words. Additional references from personal libraries were identified by the authors.

Although validated in PsA, the HAQ-DI has limitations, including marked floor effects, lack of responsiveness to treatment effects in later disease stages, and underestimation of physical impairment in patients whose symptoms are predominantly skin related. Nonetheless, it has been widely used in clinical trials of PsA treatment and is generally responsive to change with effective therapy, discriminating between active and placebo treatments. Other generic or arthritis-specific patient-reported questionnaires with a focus on physical impairment include the Medical Outcomes Study Short Form-36 Health Survey, the EuroQol-5D, the Arthritis Impact Measurement Scales, and the Routine Assessment of Patient Index Data 3. There are currently no PsA-specific instruments to assess physical function, but health-related quality-of-life questionnaires with elements related to functional impairment include the PsA Quality of Life questionnaire, the PsA Impact of Disease questionnaire, and VITACORA-19. As the available measures of physical impairment may not reflect the impact of all aspects of PsA on a patient, additional health-related quality-of-life instruments, such as the Dermatology Life Quality Index, may be used in parallel to obtain a more complete picture of the disease burden.

The HAQ-DI is a valuable assessment tool that clinicians should continue to use in clinical trials and practice. Because instruments to specifically assess physical function in patients with PsA are currently lacking, clinicians should consider using a combination of instruments to conduct the most thorough evaluation possible.