Low frequency of anticyclic citrullinated peptide antibodies in psoriatic arthritis but not in cutaneous psoriasis.

BACKGROUND: Anticyclic citrullinated peptide (anti-CCP) antibodies are highly specific for the diagnosis of rheumatoid arthritis (RA). The clinical distinction between RA and psoriatic arthritis (PsA) is often difficult to establish; therefore, the presence of rheumatoid factor (RF) and anti-CCP antibodies could be useful. Seven percent to 40% of patients with longstanding psoriasis will develop PsA at some point. Therefore, it is important to study the positivity of these antibodies in these two interrelated populations.

OBJECTIVE: The aim of this study was to determine the seropositivity of anti-CCP antibodies in patients with psoriasis and PsA and to compare it with that seen in patients with other inflammatory, noninflammatory (osteoarthritis) arthritides and healthy controls.

PATIENTS AND METHODS: Serum anti-CCP antibodies were measured in 106 patients with cutaneous psoriasis, 72 patients with PsA, 41 healthy controls (HC), 41 patients with undifferentiated or early inflammatory arthritis (UA), and 41 patients with RA and 41 with osteoarthritis using a commercial second-generation enzyme-linked immunosorbent assay. We considered a positive result to be >20 UI/mL, as recommended by the manufacturer.

RESULTS: Of 106 patients with PsA, 55 were women and 51 men. The mean age was 42.87 +/- 17.71 years and the mean disease duration was 5.3 +/- 2.10 years. Anti-CCP antibodies were not present in patients with psoriasis without arthritis. In contrast, 7 of 72 (9.72%) patients with PsA were positive for anti-CCP antibodies with a median titer of 7.16 units. Only one patient with PsA was positive for RF. Most of these patients were female with polyarticular joint involvement. Distal interphalangeal involvement was present in 4 and 2 had dactylitis. We found clear differences when we compared patients with PsA with patients with psoriasis (P = 0.001). Of the 43 patients with UA studies, 4 initially exhibited a low titer positive anti-CCP antibody, and at follow up, another patient developed anti-CCP antibodies and later developed RA. None of the patients with UA developed PsA at 5-year follow up. Thirty-two of the 41 patients had a positive anti-CCP antibody and the mean +/- standard deviation of the anti-CCP units was 80.61 +/- 55.5.2. Six of the 41 (14.6%) patients with osteoarthritis studied had positive anti-CCP with a mean titer of 7.388. None of the healthy controls exhibited positively for anti-CCP antibodies.

CONCLUSION: Anti-CCP antibodies may be found in patients with PsA and not in our patients with only cutaneous psoriasis. These antibodies may also be found in some patients with osteoarthritis and rarely in patients with UA; such patients will be of interest to follow prospectively.