Bristol rheumatoid arthritis fatigue scale is valid in patients with psoriatic arthritis and is associated with overall severe disease and higher comorbidities.

Aims: To (1) determine the reliability and validity of the Bristol Rheumatoid Arthritis Fatigue scale (BRAF-NRS) in patients with psoriatic arthritis (PsA) and (2) examine possible clinical associations of worse fatigue in PsA.

Methods: Study phase 1: BRAF-NRS scale validation cohort. A consecutive cohort of 70 PsA patients was recruited to complete the 3-item BRAF-NRS and the 13-item Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) questionnaires, alongside disease activity assessment. All patients also completed the BRAF-NRS questionnaire, 1 day later. Study phase 2: Identifying the potential clinical associations of fatigue by using BRAF-NRS (n = 283). A second cohort of 283 PsA patients underwent detailed skin and rheumatologic assessments including disease activity measures. Comorbidities were measured using the Charlson comorbidity index (CCI). Factors predicting worse fatigue as measured by BRAF-NRS were determined using regression analysis.

Results: In phase 1, 67 out of 70 patients from the first cohort had complete assessments. The internal consistency of BRAF-NRS as measured by Cronbach's alpha was 0.92. Test-retest reliability as measured by the intra-class correlation coefficient was 0.97. There was excellent correlation between the BRAF-NRS and FACIT-F score(r = - 0.83) (p = <0.001, 95% CI - 0.74 to - 0.91). In phase 2, using data from the second cohort of 283 PsA patients, possible clinical associations of worse fatigue were examined. On multiple linear regression analyses, the model predicted significant association of worse fatigue scores with low education status (p = 0.03), number of deformed joints (p = 0.01), not achieving minimal disease activity state (p < 0.001), higher CCI scores, and worse health assessment questionnaire score (p < 0.001).

Conclusions: BRAF-NRS is a reliable, reproducible, and valid instrument for measuring fatigue in PsA. Fatigue in PsA is associated with low education status and overall more severe disease.Key Points• Fatigue is increasingly recognized as an important measure to examine among patients with PsA, but the available valid fatigue scores in PsA are relatively long and time-consuming especially when other core domains also need to be measured• BRAF-NRS is a short, easily readable, only 3-item tool to measure fatigue, and this is the first study which has examined its performance among the patients with PsA. Our results show that it is a reliable, reproducible, and valid (construct validity) instrument for measuring fatigue in PsA• This study also clearly showed a significant positive relationship between fatigue and comorbidities, and it was also found that comorbidities play the largest role in the multivariate model.