Differentiating psoriatic arthritis sine psoriasis from seronegative rheumatoid arthritis-Experiences from five patients.

Psoriatic arthritis (PsA) without skin lesions is frequently confused with seronegative rheumatoid arthritis (RA). In this study, we aimed to promote diagnostic accuracy. Five PsA patients with no skin lesions were reviewed. We analyzed the clinical characteristics of these patients. All patients had multiple peripheral arthritis as well as axial involvement, and had been misdiagnosed with RA for several years initially. They developed severe deformation as a result of delayed diagnosis and inadequate treatment. Four patients had nail changes and one had a family history of psoriasis. They had hallmarks of PsA such as dactylitis, enthesitis, and distal interphalangeal arthritis. Ultrasound detection frequently revealed inflammation in the enthesis and extra-synovial areas. Nail psoriasis, dactylitis, enthesitis, distal interphalangeal arthritis, and extra-synovial inflammation would help to differentiate PsA from seronegative RA.