Early Psoriatic Arthritis Versus Early Seronegative Rheumatoid Arthritis: Role of Dermoscopy Combined with Ultrasonography for Differential Diagnosis

Objective Exclusion of psoriatic skin/nail lesions is important in differentiating early seronegative rheumatoid arthritis (ERA) from early polyarticular psoriatic arthritis (EPsA) and such manifestations may go unnoticed in atypical or minimally expressed cases. The aim of this study is to assess the usefulness of integrated rheumatological-dermatological evaluation in highlighting dermatological lesions missed on rheumatological examination and to investigate the role of ultrasonography (US) and dermoscopy in improving the recognition of subclinical psoriatic findings. Methods Patients with a new diagnosis of seropositive or seronegative ERA and EPsA with prevalent hands involvement were recruited. All were reassessed for the presence of psoriatic lesions during an integrated rheumatological-dermatological clinical evaluation and underwent hands US and proximal nailfold dermoscopy. Results Seventy-three consecutive subjects were included in the study: 25 with seropositive ERA, 23 with seronegative ERA, and 25 with EPsA. One-fourth of the subjects initially diagnosed as seronegative ERA presented cutaneous or nail psoriasis on integrated rheumatological-dermatological evaluation, thereby being reclassified as EPsA. The presence of at least 1 extrasynovial feature on hand US and dotted vessels on proximal nailfold dermoscopy was significantly associated with EPsA, with a sensitivity of 68.0% and 96.0% and a specificity of 88.1% and 83.3% for US and dermoscopy, respectively. When used together, specificity for PsA diagnosis raised to 90.5%. Conclusion Integrated rheumatological-dermatological clinical evaluation may be helpful in identifying patients with EPsA misclassified as seronegative ERA. Additionally, US and dermoscopy may be used as supportive tools in identifying subclinical psoriatic features, which may come in handy in distinguishing EPsA from ERA.