Abstract

Objective: Fatigue is an important symptom in psoriatic arthritis (PsA). The aim of this study was to determine the reliability and validity of the Functional Assessment of Chronic Illness Therapy Fatigue Scale (FACIT-Fatigue) in PsA.

Methods: Consecutive patients attending the PsA Clinic completed the FACIT-Fatigue twice, one week apart. Patients were assessed clinically according to a standardized 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 with other fatigue measures and disease characteristics.

Results: 135 patients (80M/55F, mean age 52±13yrs, disease duration 17±10 yrs) participated. The mean FACIT-Fatigue score was 35.8±12.4. Cronbach’s alpha was 0.96. Repeat questionnaires were returned by 54% of patients. There was no difference in disease characteristics 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 - 0.79 (95% CI -0.85, -0.72). FACIT-Fatigue scores were lower in patients with overwhelming fatigue and fibromyalgia than those without (p<0.0001). FACIT- Fatigue was correlated with actively inflamed joint count (-0.43, 95% CI -0.56, -0.28, p<0.0001), but not with the clinically damaged joint count (-0.06, 95% CI - 0.23, 0.11, p=0.51).

Conclusion: The FACIT-Fatigue was reproducible, 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.