Background Psoriasis patients attending outpatient dermatology clinics may have musculoskeletal complaints that relate to psoriatic arthritis (PsA). Dermatologists are recommended to ask patients about characteristic signs of inflammatory joint disease, allowing an early detection and treatment of PsA. Several screening tools have been proposed to help general practitioners or dermatologists detecting patients with PsA, but none combines appropriate diagnostic value and ease of use compatible with outpatient practice.
Objectives To develop and internally validate a brief tool for dermatologists to screen patients to refer to a rheumatologist for PsA diagnosis.
Methods After extensive literature review, 12 items were initially selected, covering various locations (peripheral joints, spine, buttock, anterior chest wall, fingers, heel) and features of inflammatory signs occurring in PsA (morning stiffness, nocturnal awaking, swollen joint). The validation study was conducted in patients with psoriasis diagnosed by a dermatologist consecutively recruited between 09/2012 and 06/2014 (Saint Joseph Hospital, Paris, France). Patients already known to be affected by PsA were excluded. After being enrolled by a dermatologist, participants were subsequently assessed by a rheumatologist who assessed the diagnosis of PsA based on CASPAR criteria (Yes/No). Univariate analysis was first conducted to examine associations between items and PsA diagnosis. Multivariate logistic regression models using Firth's penalized likelihood method were then performed, following a stepwise backwards procedure. Weights were rescaled from the regression coefficients to provide the final score. Model discrimination was assessed through sensitivity (Se), specificity (Sp), positive (PPV) and negative predictive values (NPV), and area under the ROC curve (AUC). Final model was internally validated using bootstrapping techniques.
Results 168 patients were recruited, of whom 9 were excluded for previously established PsA and 22 were lost-to-follow up and did not attend the rheumatologist consultation. Of the 137 included patients (median age 43 [interquartile range 31-55], 59.6% men, median duration of psoriasis disease 12 [5-20]), 21 (15.3%) had a final diagnosis of PsA. Final logistic regression model included 6 independent items, including past or current dactylitis, inflammatory heel pain, bilateral buttock pain, anterior chest wall pain, peripheral joint pain with swelling, and back pain with prolonged morning stiffness. At the optimized threshold of ≥1/10 points, the final score yielded the following performance indices: Se=90.5% (69.6-98.8), Sp=74.1 (65.2-81.8), PPV=38.8 (25.2-53.8), NPV=97.7 (92.0-99.7), AUC=89.0 (80.7-97.3; Figure). No evidence for overoptimism was found in internal validation.
Conclusions These first findings demonstrate the good diagnostic properties of a new screening scale using only 6 easy to collect items. If confirmed in other populations, these features may prove useful in outpatient dermatology clinics for selection of psoriasis patients requiring further assessment by the rheumatologist.
Disclosure of Interest None declared