Validity and Psychometric Properties of 3 and 4 Visual Analog Scale in Participants With Psoriatic Arthritis Treated With Guselkumab

OBJECTIVE: To evaluate the validity of the 3-item Visual Analog Scale (3VAS) and 4VAS and determine the minimal clinically important difference (MCID) and minimal detectable change (MDC) for each measure using data from three phase 3 randomized clinical trials of guselkumab in psoriatic arthritis (PsA).

METHODS: Pooled data (1,405 participants) from the DISCOVER-1, DISCOVER-2 and COSMOS studies were used. 3VAS/4VAS MCID and MDC were estimated using established formulae. Receiver operating characteristic analysis was used to identify 3VAS/4VAS thresholds for low, moderate and high disease activity. Criterion validity was assessed by correlating 3VAS/4VAS with other PsA measures. Mixed models evaluated the association between changes from baseline in 3VAS/4VAS at Week (W)8 of guselkumab treatment with the total PsA-modified van der Heijde-Sharp (vdH-S) score through W100.

RESULTS: 3VAS/4VAS showed moderate-to-strong correlation with all outcome measures assessed, with coefficients ranging from 0.56/0.62 for Health Assessment Questionnaire-Disability Index to 0.92/0.94 for patient global assessment. MCID was 0.9 for both 3VAS (range 0.7-1.3 depending on method used) and 4VAS (0.6-1.3); MDC was 3.1 and 3.0, respectively. 3VAS cutoffs for low, moderate and high disease activity were 2.1, 3.3 and 4.8, respectively, and 2.1, 3.4 and 5.0 for 4VAS. Change in 4VAS at W8 of guselkumab treatment significantly associated with change in vdH-S score through W100 (P=0.039).

CONCLUSION: These analyses support the validity of 3VAS/4VAS as multidimensional measures of PsA disease activity. 4VAS may be preferred owing to its greater face validity and separate measurements of the two cardinal aspects of PsA (joint/skin disease) and pain.