FRI0347 TUBERCULIN SKIN TEST FOR DETECTION OF TUBERCULOSIS IN SYSTEMIC SCLEROSIS

Abstract

Background The tuberculin skin test (TST) is a screening tool for detection of occult or remote tuberculosis infection. Although skin tightness is a classic manifestation in systemic sclerosis (SSc), there are no reports vis-a-vis any limitation of the TST in SSc patients nor a definition on the cut-off for a positive TSTtest size for a diagnosis of tuberculosis. Objectives Our aims were to determine (a) the indurated reaction size of the TST; (b) the cut-off size for the indurated TST; and, (c) the sensitivity and specificity of the test for the diagnosis of tuberculosis in SSc patients. Methods A cross-sectional study was conducted among Thai adult SSc patients, followed up at the Scleroderma Clinic, Khon Kaen University, Thailand between November 1, 2016 and November 30, 2017. The TST was performed using 0.1 ml purified protein derivatives (PPD) injected intradermally (Figure 1), and interpreted 72 hours after testing. Results A total of 168 SSc patients were enrolled (female to male ratio = 1.8:1). The median age and duration of disease was 57.2 and 6.4 years, respectively. The majority (71.8%) was the diffuse cutaneous SSc subset. Seventeen cases (10.1%) were defined as tuberculosis infection. All of the patients had a history of BCG vaccination at birth. An indurated skin reaction size TST of 20 U/L had a high specificity for tuberculosis (99.3%: 95%CI 96.4-100) (Kappa 0.86; p=0.03). The modified Rodnan skin score (mRSS) had a significant negative correlation with the indurated skin reaction size (Rho -0.23; p=0.003). While other clinical parameters—such as BMI, SSc subset, serum albumin level, steroid or immunosuppressant use—were not correlated with the TST result (p=0.06, 0.14, 0.09, 0.23 and 0.89, respectively). Conclusion Indurated skin ≥ 20 mm indicated a high specificity for tuberculosis infection in SSc patients with history of BCG vaccination. The high mRSS resulted in a smaller skin reaction size when using the TST. The TST is thus less useful as a diagnostic tool for tuberculosis among SSc patients, especially among those with severe skin tightness.