Functional assessment of chronic illness therapy-fatigue scale is valid in patients with psoriatic arthritis

Background: Fatigue is an important symptom in psoriatic arthritis ( PsA). Aim: To determine the reliability and validity of the Functional Assessment of Chronic Illness Therapy- Fatigue ( FACIT fatigue) Scale in PsA. Methods: Consecutive patients attending the PsA clinic were assessed with the FACIT fatigue Scale twice, 1 week apart. Patients were assessed clinically according to a standardised PsA clinic protocol. Internal consistency of the 13 items on the FACIT fatigue questionnaire was measured using Cronbach's alpha; test - retest reliability by the intraclass correlation coefficient ( ICC), and validity by the correlation of the FACIT fatigue results with other fatigue measures and disease characteristics. Results: 135 patients ( 80 men and 55 women, mean ( SD) age 52 ( 13) years, mean ( SD) disease duration 17 ( 10) years) participated. The mean FACIT fatigue score was 35.8 ( 12.4). Cronbach's a was 0.96. Repeat questionnaires were returned by 54% of patients. No difference in disease characteristics was observed between those who did and did not return the questionnaires. The ICC for first and repeat FACIT fatigue scores was 0.95. The correlation between the FACIT fatigue and modified Fatigue Severity Score was 20.79 ( 95% CI -0.85 to -0.72). FACIT fatigue scores were lower in patients with overwhelming fatigue and fibromyalgia than in those without ( p < 0.001). The FACIT fatigue was correlated with the actively inflamed joint count ( - 0.43, 95% CI - 0.56 to - 0.28, p, 0.001), but not with the clinically damaged joint count ( -0.06, 95% CI -0.23 to 0.11, p = 0.51). Conclusion: The FACIT fatigue results were reproducible, and correlated with other fatigue measures as well as with disease activity in patients with PsA. Therefore, the FACIT fatigue is a reliable and valid instrument to measure fatigue in PsA.