Department of Rheumatology, Nuffield Orthopaedic Centre, Oxford, UK
SIR, We report a study of anti-endomysial antibodies (EmA) in patients with psoriatic arthritis (PsA) in Oxford.
The presence of EmA is a useful screening test for gluten sensitivity [1], which is often unrecognized in the general population [2]. Michaëlsson et al. [3] found that 49 of 302 patients with psoriasis had increased serum IgA antibodies to gliadin. When 30 of these patients followed a gluten-free diet, their psoriasis improved [4]. Gluten sensitivity could be relevant to the underlying pathogenetic mechanisms in PsA and we aimed to ascertain the prevalence of positive EmA in a group of patients with PsA.
Ethical approval was obtained from the Central Oxford Research Ethics Committee. We invited 149 patients with PsA from the rheumatology clinics in Oxford to attend a special interest clinic for PsA. Patients were considered to have PsA if they had a seronegative inflammatory arthritis and psoriasis. Patients were excluded if their rheumatoid factor titre was >1:160 or if they had reactive arthritis with a clear infective trigger.
EmA were detected by direct immunofluorescence, as described in detail elsewhere [2]. Serum IgA was also determined to identify cases of IgA deficiency.
A total of 107 patients were finally recruited to the PsA special interest clinic between December 1998 and September 2000; eight did not respond to the letter, 17 did not attend their appointment, 11 declined, and six had other reasons for not taking part. Of the 107 participants, four attended prior to EmA being tested in our study, two were excluded as their diagnosis was not PsA (rheumatoid and reactive arthritis, respectively), one had never had psoriasis and was therefore excluded, one did not consent to venepuncture, and three blood samples did not arrive at the laboratory. Therefore 96 samples [51 males and 45 females aged between 19 and 71 yr (mean age 45.9 yr)] were collected for EmA analysis.
Endomysial antibody assays have a reported specificity of 94100% and a sensitivity of 89100% [5]; however, sensitivity was shown to be only 78% in a recent report [6]. EmA testing is currently the screening method of choice for gluten sensitivity, but this is being superseded by tissue transglutaminase ELISA (enzyme-linked immunosorbent assay), which in preliminary studies has superior sensitivity (98%) and specificity (98%) [7]. In our study all 96 patients were negative for EmA. The population prevalence of gluten sensitivity in the United Kingdom is estimated to be 0.5% [8], therefore our study shows that it is unlikely that PsA is strongly related to gluten sensitivity. Larger studies would be needed to identify the true prevalence of gluten sensitivity in PsA.
This study was supported by a research grant from the Oxfordshire Health Authority.
Notes
Correspondence to: J. L. Dockerty, Senior Registrar, Rheumatology Department, Dunedin Hospital, 201 Great King Street, Dunedin, New Zealand.
References
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