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Absence of metacarpophalangeal synovitis by high-resolution ultrasonography distinguishes psoriatic arthritis from rheumatoid arthritis – A cross-sectional study

Background: We aimed to evaluate the high-resolution ultrasonography (HRUS) findings in the hands of patients with psoriatic arthritis (PsA) and rheumatoid arthritis (RA). Materials and Methods: This was a cross-sectional study of ultrasonography (USG) of hands in patients with PsA fulfilling the Classification criteria for psoriatic arthritis (CASPAR) in comparison with cases with RA fulfilling 1987 American College of Rheumatology classification criteria. Bilateral 1st and 2nd metacarpophalangeal (MCP) and proximal interphalangeal joints were assessed for synovitis and bone erosions, and extensor tendons at wrist for tenosynovitis by a single observer using the GE LOGIQ BOOK XP USG machine (General Electric Medical Systems) with a high-frequency 12-MHz linear array transducer. Demographic and clinical details were extracted from the electronic database of the hospital information system. Results: A total of 62 patients (31 with RA and PsA each) were studied. Demographic and baseline features were similar, except for more male patients in PsA as compared to RA (41.9% vs. 16.1%; P = 0.02). MCP synovitis was higher in RA as compared to PsA (71% vs. 29%; P = 0.001). Multiple logistic regression analysis found that absence of MCP synovitis by HRUS (adjusted odds ratio [OR]: 5.97; P = 0.02) in spite of higher number of swollen joints (adjusted OR: 29.3; P = 0.03) favors the diagnosis of PsA as compared to RA. Conclusion: “Our finding of fewer or no MCP synovitis by HRUS in PsA as compared to RA warrants a larger, powered validation study; if reproduced, it can be an additional tool to differentiate PsA including those without overt skin lesions from seronegative RA/early undifferentiated polyarthritis.”