Objective: To identify isolated peripheral enthesitis and/or dactylitis as a subset of psoriatic arthritis (PsA) and to define the clinical characteristics of these patients.
Methods: We examined 401 unselected patients with PsA seen in 3 Italian rheumatological centers over a 6 month period. The diagnosis of PsA was based upon the clinical experience of a rheumatologist. The clinical features of patients with PsA were assessed by clinical examination and review of the patients' charts, evaluating the presence of peripheral arthritis, spinal involvement, dactylitis, and enthesitis. A series of 483 rheumatological patients without psoriasis and spondyloarthropathy (European Spondylarthropathy Study Group criteria) seen consecutively in a one month period constituted the control group.
Results: 14 patients (3.5%) presented isolated episodes of peripheral enthesitis and/or dactylitis. No patient developed peripheral arthritis and/or axial involvement during the followup period (median 30 mo; range 3-72 mo). 10/14 patients (71%) presented at least one episode of finger and/or toe dactylitis. 5 of these 10 patients (50%) had additional episodes of peripheral enthesitis (Achilles tendinitis, plantar fasciitis, and posterior tibial tendinitis). Episodes of Achilles tendinitis and/or plantar fasciitis were present in 8/14 patients (57%). 3 of these 8 patients (37%) had associated peripheral enthesitis in other sites as well: lateral epicondyle, insertion of the patella tendon into the inferior pole of the patella, femoral quadriceps, and posterior tibial tendons. An additional case had posterior tibial tendinitis and 2 episodes of toe dactylitis. None of these 14 cases presented radiological evidence of sacroiliitis and only one of the 13 typed was HLA-B27 positive. 12 patients (2.4%) of the control group had episodes of peripheral enthesitis (11 plantar fasciitis and one Achilles tendinitis). No patient had episodes of dactylitis. The frequency of isolated Achilles tendinitis and/or dactylitis was significantly higher in patients with PsA compared to controls (3.5 vs 0.2%; p = 0.001).
Conclusion: In some patients PsA can occur only with peripheral enthesitis, particularly Achilles tendinitis, and/or dactylitis. These patients may represent a subset of PsA, not defined by Moll and Wright and spondyloarthritis classification criteria, and poorly recognized in the studies on PsA.