ANTI-TNF THERAPY DOES NOT SUPPRESS TST RESPONSE IN RHEUMATOID ARTHRITIS PATIENTS

Background: In RA patients, tuberculosis (Tb) is increasing, mainly as result of latent infection (LTB1), a serious complication of treatment with anti-TNF. TNF blockade induces antiinflammatory and immunosuppressive effects, and at least theorically, it would be reasonable to expect that anti-TNF may suppress the tuberculin skin test (TST). Miss-application, the booster phenomenon (enhancement of TST on repeated testing 1-4 weeks after a negative resut) and interobserver variation are other important considerations regarding TST measure. However we have been unaware of formal data in rheumatic diseases.Objectives: To determine in RA patients the possible anti-TNF treatment effect on TST response and, b) to reassess the interobserver reliability in measuring TST response.Methods: We studied 37 RA patients (26 women, 11 men, mean age 42 ± 18.3 years) TST1 with booster (5 IU 23RD, Tubersol®), was applied to them, before starting anti-TNF therapy: 25 with adalimumab (ADA, 40 mg SC c/14 d), 12 with infliximab (INF, 3 mg/kg). Initial TST response (pre-anti-TNF therapy), was determined measuring the transverse diameter of the induration by the rolling method at 72 hours (TST1). The second TST application (TST2) was made 24 weeks after start anti-TNF therapy. They were measured by 2 independent observers and the average reading was taken for analysis. Interobserver reliability was tested by kappa coefficient. As controls, we used 20 inactive RA patients treated with chloroquine (RA-CQ), 6 men and 14 women, with age 43 ± 17.2 years SD. TST1 was measured already started CQ therapy, and TST2 was tested 24 weeks after TST1.Results: In RA patients with anti-TNF therapy, initial average induration (TST1) was 3.9 ± 7.2 mm SD and 4.3 ± 6.8 mm SD at 24 weeks of treatment (TST2), compared with TST1 of 4.2 ± 6.5 mm SD and TST2 of 4.5 ± 6.6 mm SD in RA-CQ group (p NS). An amplification or "booster"(defined as an increase >5 mm when TST1 was <10mm) was observed in 3/37 (9%) of anti-TNF patients and in 2/20 (10%) of RA-CQ patients (p NS). In 4 patients with negative TST1 (2 with INF, 1 with ADA, 1 RA-CQ), TST2 was positive (increase >5 mm), and in 3 TST1+ RA patients, a negative TST2 was observed (1 with INF, 1 with ADA, 1 RA-CQ), although all had negative bacilloscopy and normal chest X-ray, without clinical evidence of active Tb. The interobserver reliability was quite good with a kappa coefficient of the 0,78 when taking the cut-off for TST+ <5mm and of 0,89 when the cut-off was <10mm.Conclusion: In RA patients, anti-TNF therapy does not suppress or modify substantially TST response to 6 months of treatment compared with CQ, and TST interobserver reliability was enough acceptable for a biological test.Citation: Ann Rheum Dis, volume 64, supplement III, year 2005, page 409Session: Rheumatoid Arthritis – Treatment