Background/Purpose: The prevalence of undiagnosed psoriatic arthritis (PsA) in psoriasis patients is high, with delays in diagnosis contributing to poor patient outcomes. We aimed to describe a novel model of care involving a self-referral system and central triage clinic for psoriasis patients with musculoskeletal (MSK) symptoms and to compare the efficacy of several triage methods for PsA.

Methods: Patients with psoriasis were identified by searching the institutional electronic medical records. These patients received a letter inviting them to contact the research team if they were experiencing any MSK symptoms. Participants were assessed in a central triage clinic to determine their likelihood of having PsA. The following triage methods were used: 1) three PsA screening questionnaires (TOPAS-2, PEST, PASE); 2) MSK ultrasound assessment of symptomatic joints and entheses; 3) clinical assessment by an advanced practice physiotherapist and 4) levels of CRP and ESR. Each patient was then assessed by a rheumatologist to determine whether they have PsA. Patients were classified by the rheumatologist to “Not PsA”, “Possible PsA” or “PsA”. The rheumatologist was blinded to the results of the triage methods. The performance of each triage method to identify PsA was assessed by calculating its sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the ROC curve (AUC).

Results: Of the 1159 patients invited to participate, 300 responded (26%) and 152 (13%) agreed to participate. Of the 94 patients assessed thus far in the clinic, 69 (73%) did not have PsA, 17 (18%) had possible PsA, and 8 (9%) had PsA. The performance of triage methods is presented in Table 1. The advanced practice physiotherapist’s assessment in detecting clinical PsA was highly sensitive (100%) with good specificity (71%). The screening questionnaires varied by their sensitivity and specificity with TOPAS-2 showing highest sensitivity (88%) and PASE with highest specificity (87%). The prevalence of positive MSK inflammation by ultrasound (at least 1 joint or enthesis with positive power Doppler signal) was 39.4%. The sensitivity of positive MSK ultrasound was high (88%) but its specificity was moderate (65%). 22% of the study participants who had positive MSK ultrasound findings were not classified by the rheumatologist as having PsA. The performance of CRP and ESR as triage methods was poor.

Conclusion: MSK ultrasound, advanced practice physiotherapist and TOPAS-2 were highly sensitive in identifying patients with PsA among psoriasis patients with MSK symptoms. A significant proportion of patients with positive MSK inflammation by ultrasound were not identified as having PsA by the clinician.