Musculoskeletal ultrasound can improve referrals from dermatology to rheumatology for patients with psoriasis

Dear Editor, Psoriasis affects 1–3% of the population, and up to one‐third of patients with psoriasis have underlying psoriatic arthritis (PsA).1 Nonspecific musculoskeletal complaints are even higher, occurring in around 50% of patients.2 Detecting early signs of PsA and providing early treatments are crucial to prevent progressive, damaging arthritis.3 Due to the high frequency of nonspecific pain in psoriasis, it is not possible for every patient with psoriasis with joint pain to be assessed by a rheumatologist. Different screening tools have been developed for the dermatology practice to distinguish patients with a higher likelihood of having PsA; however, the low specificities of these tools limit their use in clinical practice.4,5,6 Musculoskeletal ultrasound (US) has been shown to be more sensitive than physical examination to detect joint inflammation.7 It has been used commonly in rheumatology practice for diagnosis and follow‐up of patients with inflammatory arthritis including PsA. We hypothesize that a screening US could add value to improve referrals from dermatology to rheumatology for patients with psoriasis with joint pain. To test our hypothesis a prospective study on patients with psoriasis with any joint pain was carried out (Ottawa Health Science Network Research Ethics Board, Ottawa: 20160386‐01H). Exclusion criteria included already known diagnosis of PsA, recent trauma or surgery of the painful joints, and pregnancy. After giving informed consent, patients had an US scan on the same day as their clinical assessment by one of two experienced rheumatologists in musculoskeletal US, blinded to the clinical examination findings (S.B. or D.S.). A predefined limited US protocol was performed, examining the wrists and 2–3rd metacarpophalangeal, 2–3rd proximal interphalangeal and 2–5th metatarsophalangeal joints for synovitis, and also Achilles enthesitis and the most painful joint. The US scoring system included a semiquantitative scoring of inflammation (none, mild, moderate, severe) for both grey‐scale and Doppler findings. A similar approach was used to compare the inflammatory entheseal findings. The Early Arthritis for Psoriatic Patients6 and Psoriasis Epidemiology Screening Tool5 questionnaires were completed by the patients. After reviewing these questionnaires the dermatologist was asked to make a decision on the indication to be referred to rheumatology. Then, the US information was shared with the dermatologist using a standard report form, and the decision of referral was revisited. The patients were then assessed by a rheumatologist. The accuracy of the referrals based on the questionnaires and dermatologist's assessment was investigated and the added value of US was analysed. Fifty‐one patients with psoriasis with a median age of 48 years (interquartile range 38–60, range 21–68) were enrolled. The most common psoriasis type was plaque psoriasis (86%), with a median 15 years (interquartile range 6–30, range 2–58) of disease duration. PsA was diagnosed in 20 patients (39%) according to the rheumatologist. Based on the questionnaires, the dermatologist decided to refer 47 patients (92%) with psoriasis to rheumatology. Among these 19 (40%) were diagnosed with PsA, showing high sensitivity (95%) but low specificity (9%) of the referrals based on clinical assessment only. After reviewing the US scans, 22 patients were referred to rheumatology, with a reduction of 53%. Among these, 15 (68%) were diagnosed with PsA. Among nonreferred patients, five were diagnosed with PsA but two had isolated axial involvement with no peripheral joint disease, for which the peripheral joint and entheseal US would not be expected to have any value. After exclusion of these cases, the sensitivity and specificity of the referral by the dermatologist were found to be 88% and 77%, respectively (Table 1). Performance of the questionnaire and added value of ultrasound (US) CI, confidence interval; EARP, Early Arthritis for Psoriatic Patients; LR, likelihood ratio; NPV, negative predictive value; OR, odds ratio; PEST, Psoriasis Epidemiology Screening Tool; PPV, positive predictive value. Performance of the questionnaire and added value of ultrasound (US) CI, confidence interval; EARP, Early Arthritis for Psoriatic Patients; LR, likelihood ratio; NPV, negative predictive value; OR, odds ratio; PEST, Psoriasis Epidemiology Screening Tool; PPV, positive predictive value. Timely referral of patients with psoriasis to rheumatology is an important step in the management of PsA and improves long‐term patient outcomes. Screening tools in psoriasis that have high sensitivities usually have low specificities, which means a higher number of patients to be referred to rheumatology than needed.4,8 This is a concern due to high patient loads within rheumatology clinics and long waiting times. Our study demonstrated that a musculoskeletal US based on a predefined protocol improves the referrals made to rheumatology. In conclusion, a screening musculoskeletal US in patients with psoriasis with peripheral joint pain improves the referrals from dermatology to rheumatology by decreasing the false positives. The screening by US in this study was done by experienced rheumatologists; therefore, whether the same results can be achieved by less experienced sonographers with no special interest in musculoskeletal US needs to be studied to test the generalizability of the tool for this indication. If the same results can be achieved, a screening programme that involves a family physician or a healthcare professional and a sonographer may be useful to identify patients who have higher risk of PsA and improve the referrals to rheumatology. Funding sources: this study was supported by AbbVie. D.S. had funding from Union Chimique Belge (UCB) Canada for an axial spondyloarthritis fellowship. S.B. had funding from the Turkish Society for Rheumatology. Conflicts of interest: S.Z.A. has received honoraria from AbbVie, Celgene, UCB, Novartis, Janssen and Sanofi. S.F. did not receive funding for this study. She has received honoraria and served on advisory consultancy boards for AbbVie, Actelion, Aralez, Bausch Health, Celgene, Janssen, LEO Pharma, Novartis, Pfizer, Sanofi Genzyme and UCB.

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