International multicenter psoriasis and psoriatic arthritis reliability trial for the assessment of skin, joints, nails, and dactylitis.

Objective: Clinical trials in psoriasis and psoriatic arthritis (PsA) involve assessment of the skin and joints. This study aimed to determine whether assessment of the skin and joints in patients with PsA by rheumatologists and dermatologists is reproducible.

Methods: Ten rheumatologists and 9 dermatologists from 7 countries met for a combined physical examination exercise to assess 20 PsA patients (11 men, mean age 51 years, mean PsA duration 11 years). Each physician assessed 10 patients according to a modified Latin square design that enabled the assessment of patient, assessor, and order effect. Tender joint count (TJC), swollen joint count (SJC), dactylitis, physician's global assessment (PGA) of PsA disease activity (PGA-PsA), psoriasis body surface area (BSA), Psoriasis Area and Severity Index (PASI), Lattice System Physician's Global Assessment of psoriasis (LS-PGA), National Psoriasis Foundation Psoriasis Score (NPF-PS), modified Nail Psoriasis Severity Index (mNAPSI), number of fingernails with nail changes (NN), and PGA of psoriasis activity (PGA-Ps) were assessed. Variance components analyses were carried out to estimate the intraclass correlation coefficient (ICC), adjusted for the order of measurements.

Results: There is excellent agreement (ICC >/=0.80) on the mNAPSI, substantial agreement (0.6 >/= ICC < 0.80) on the TJC, PASI, and NN, moderate agreement (0.4 >/= ICC < 0.60) on the PGA-Ps, LS-PGA, NPF-PS, and BSA, and fair agreement (0.2 >/= ICC < 0.40) on the SJC, dactylitis, and PGA-PsA. The only measure that showed a significant difference between dermatologists and rheumatologists was dactylitis (P = 0.0005).

Conclusion: There is substantial to excellent agreement on the TJC, PASI, NN, and mNAPSI among rheumatologists and dermatologists.