In patients with PsA, the severity of nail disease correlates with indicators of severity of both skin and joint disease. Although rheumatologists can adequately screen for nail disease, the management of this aspect of PsA is often overlooked.
administration and in interpreting the results, particularly in the context of previous bacille Calmette-Guérin (BCG) vaccination. 3 Of newly diagnosed patients with pulmonary tuberculosis, 10-25% will have false-negative skin tests. This is due to a combination of factors, including inadequate nutrition, the inability to react to skin tests due to immunosuppression or the release of specific cytokines liberated in active tuberculosis which inhibit the delayed hypersensitivity, severe tuberculosis or concomitant corticosteroid use.A whole-blood IGRA for the detection of LTBI is an in vitro T cell-based assay. The principal of the assay is that T cells of individuals previously sensitized with tuberculous antigen will produce IFN-c when they re-encounter mycobacterial antigens. Thus a high level of IFN-c production is presumed to be indicative of tuberculosis infection. Early assays used purified protein derivative as the stimulating antigen; however, newer assays use RD1 antigens specific to M. tuberculosis. These antigens are not shared with BCG or most nontuberculous mycobacteria. Currently, two methods exist for detecting the IFN-c released by the T cell: an enzyme-linked immunosorbent assay (e.g. QFT-TB) and an enzyme-linked immunospot assay (e.g. T-SPOT.TB; Oxford Immunotech, Abingdon, U.K.).A recent meta-analysis found that the new IGRAs were a useful diagnostic tool with excellent specificity in the diagnosis of LTBI but concluded that further research was required to define their use in high-risk populations. 4 A systematic review recommended the use of RD1 antigen-based assays in preference to those based on a TST for the diagnosis of LTBI, especially in the context of previous BCG vaccination or immunocompromise. 5 The U.S. Centers for Disease Control and Prevention published guidance for the use and interpretation of the QFT-TB test and recommend that these tests can be used safely in all circumstances in which the TST is currently used. 6 In summary, we found the QFT-TB test to be useful in the confirmation of suspected latent tuberculosis in the management of erythema induratum. These new IFN-c assays may provide a reliable and more easily administered alternative to TSTs.
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