PsA-Disk, a novel visual instrument to evaluate psoriatic arthritis in psoriatic patients: an Italian derma-rheuma multicentre study

BACKGROUND: Consensus among dermatologists and rheumatologists in the diagnosis and assessment of musculoskeletal diseases in psoriasis (PsO) patients is needed. This study assesses characteristics of musculoskeletal pain in patients with PsO for the presence of psoriatic arthritis (PsA) and evaluation of a novel 16-item visual instrument (PsA-Disk). METHODS: Data were collected from eight dermatological/rheumatological centres across Italy. Patients with PsO completed PEST (Psoriasis Epidemiology Screening Tool) and PsA-Disk questionnaires during the first visit. A rheumatological visit was performed to confirm the presence of PsA. Both validity and reliability of PsA-Disk were assessed. RESULTS: A total of 573 patients with PsO were examined at the first visit, and 120 (21%) were diagnosed with PsA. Patients with PsA compared with patients with PsO (n = 119) presented statistically significant differences for: nail involvement, PEST score ⩾3, higher erythrocyte sedimentation rate (ESR), Nail Psoriasis Severity Index (NAPSI)-feet, NAPSI-(hands + feet) and PsA-Disk scores (73.9 ± 32.1 versus 58.1 ± 39.8, p < 0.001). Patients with PsA with knee arthritis had higher PsA-Disk scores (98.4 ± 26 versus 71.5 ± 31.9, p = 0.006) that were also correlated with number of swollen (r = 0.2, p < 0.05) and tender joints (r = 0.24, p = 0.021), patient (r = 0.4, p < 0.001) and physician-pain-visual analogue scale (VAS; r = 0.33, p < 0.001), patient global assessment (PGA)-VAS (r = 0.23, p = 0.025), physician-health assessment questionnaire (HAQ; r = 0.38, p = 0.011), Disease Activity Score (DAS)-44 (r = 0.25, p = 0.023) and Disease Activity in Psoriatic Arthritis (DAPSA; r = 0.31, p = 0.005). The instrument had excellent reliability in terms of internal consistency (Cronbach's alpha = 0.90) and stability (intraclass correlation = 0.98). Moderate agreement between PsA-Disk and PEST (Cohen's kappa = 0.46) was observed, while construct validity appeared appropriate [PsA + patients: PsA-Disk score (interquartile range; IQR) =71 (50-96); PsA-patients: PsA-Disk score (IQR)=50 (20-90); p < 0.001]. CONCLUSION: PsA-Disk may be considered a valid novel instrument aiding both dermatologists and rheumatologists in the rapid detection and assessment of musculoskeletal disease characteristics.