Diagnostic accuracy of Quantiferon TB test for patients with SLE and miliary tuberculosis

Excerpt

The mortality rate of patients with miliary tuberculosis is almost 20%. The sensitivity of acid-fast staining method does not exceed 50% for diagnosis of miliary tuberculosis. Nevertheless, the time required for mycobacterium culture results may lead to significant delay in diagnostic procedure. The tuberculin skin test is negative in more than 50% of patients with miliary tuberculosis. This is more distinct in patients who received steroid treatment. The sensitivity (86–89%) and specificity (94–98%) of QuantiFERON TB-2G (QFT-TB) test is high for the diagnosis of tuberculosis infection and the test is introduced to the clinical applications for diagnosis of active pulmonary tuberculosis. On the other hand, there are only case reports about the value of QFT-TB test in patients with miliary tuberculosis[1‐4]. In the present report, 24 years old female, who was followed with the diagnosis of systemic lupus erythematosus (SLE) and systemic sclerosis since 2005 at another health care center and was given prednisolone (by reducing gradually from 35 mg/day to 10 mg/day) and methotrexate 7.5 mg/week for last 3 years, admitted with complaints of fever, weight loss (5 kg in 3 months) and abdominal discomfort. On physical examination, she had cachectic appearance, her body temperature was 38.1°C and heart rate was 120 beats/min. On chest auscultation, coarse crackles were audible in the bilateral lung fields. The significant laboratory findings included: haemoglobin 6.9 g/dl, leucocyte count 2,200 μl⁻¹ (absolute lymphocyte count 330 μl⁻¹), platelet count 416,000 μl⁻¹, serum albumin 3.1 g/dl, erythrocyte sedimentation rate 90 mm/h, C-reactive protein 9.4 mg/dl (0–0.8 mg/dl). A chest radiograph revealed diffuse small nodular shadows in both lung fields; chest computed tomography showed multiple millimetric nodules which were consistent with miliary tuberculosis and endobronchial invasion. Subcapsular liver collection, diffuse thickening on the caecum wall and intraabdominal lymphadenopathies were revealed by abdominal computed tomography. Even though tuberculin skin test was anergic, QFT-TB test was negative and acid-fast staining in sputum and abdominal fluid samples were negative, antituberculous treatment was administered because of radiological evidence of tuberculosis and immunosuppressive status of the patient. The patient was defervesced within 3 days and on her follow-up clinical recovery was observed. Mycobacterium tuberculosis was isolated in abdominal fluid and sputum samples in the 3rd week. The data about the clinical application of QFT-TB test in miliary tuberculosis is inadequate. Kobashi et al. [3] presented one patient with indeterminate QFT-TB test who died from miliary tuberculosis. The authors suggested that lymphocytopenia caused a decrease in the production of interferon (IFN)-γ and mitogen QFT-TB levels. In another study, four of five active tuberculosis patients with indeterminate QFT-TB results had moderate lymphocytopenia (lymphocyte count <1,000 μl⁻¹) due to underlying diseases. Interestingly, one of these patients had SLE [4]. Similarly, the lymphocyte count of our patient was significantly low and she had history of receiving steroid and methotrexate. In conclusion, the diagnostic value of QFT-TB test may be controversial in a patient who had miliary tuberculosis and lymphocytopenia and/or received steroid treatment. Further investigations are necessary to determine the value of QFT-TB test in such patients. …