Validation of the Japanese version of the Systemic Lupus Activity Questionnaire that includes physician-based assessments in a large observational cohort.

The Systemic Lupus Activity Questionnaire (SLAQ) is a patient-reported outcome for systemic lupus erythematosus (SLE). We aimed to translate it into Japanese and further investigate its validity and reliability. The English version of the SLAQ was translated into Japanese and administered to Japanese SLE patients at our university clinic. Physicians assessed disease activity using the SLE Disease Activity Index 2000 (SLEDAI-2K). The patients were prospectively followed for repeat assessment a year later. Ultimately, 255 patients participated. The patients' 10-point ratings of disease activity and SLAQ scores were significantly correlated (Spearman's ρ = 0.53). The SLAQ score was weakly correlated with the SLE Disease Activity Index 2000 (SLEDAI-2K)-nolab (omitting laboratory items; ρ = 0.18) but not with the SLEDAI-2K (ρ = 0.02). These results suggested its convergent and discriminant validity. The SLAQ demonstrated acceptable internal consistency (Cronbach's α = 0.80), and good test-retest reliability (intraclass correlation coefficient = 0.85). The effect sizes and the standardized response means of the SLAQ were as follows: clinical worsening, 0.26 and 0.31, and improvement, -0.39 and -0.41, respectively, which indicated a small but significant responsiveness. The Japanese version of the SLAQ demonstrated acceptable reliability and validity; its performance was comparable to that of the original version.