13. Tuberculosis 107
Chest imaging with a CT scan may also show a nonspecific “tree in bud pattern” in some cases. Nodules, effusions, or a miliary pattern may be present; however, 5% of cases have normal chest imaging. 2. Imaging studies for extrapulmonary tuberculosis depend on the site of infection. CT scan of the chest may show hilar or cervical adenopathy as well as pericardial effusions or calcification. Echocardiography may also show pericardial effusion. Conventional X-ray, CT, and MRI may diagnose skeletal TB disease. V. Diagnosis of Tuberculosis Disease. The diagnosis of TB is based on a combination of exposure history, clinical findings, laboratory testing, and radiographic data. A. Pulmonary TB. This infection can be AFB smear-positive or smear-negative. 1. Smear-positive disease. The rapid identification of M tuberculosis should be sought with NAATs to distinguish MTB from nontuberculous mycobacteria for treatment initiation; however, culture is required to confirm the diagnosis and to establish sensitivities to antituberculosis drugs. 2. Smear-negative disease. The results of NAATs and/or culture may establish the diagnosis. Treatment should be initiated prior to microbiologic confirmation if TB is suspected and the patient is seriously ill and/or there is a high risk to transmit disease. If empiric therapy is initiated, patients should show signs of clinical response within 2 to 3 weeks (all patients should respond by 8 weeks). B. Extrapulmonary TB. These manifestations are often more difficult to diagnose as AFB smears and cultures are less sensitive. Whenever possible, tissue should be collected for histology, smear, and culture. The diagnosis may eventually be made on clinical grounds with the support of a positive TST or IGRA. VI. Screening and Diagnosis of Latent Tuberculosis Infection A. Screening. The goal of screening for LTBI is to identify persons who are at increased risk for developing active TB disease and would benefit from treatment of LTBI. Hence a decision to test presupposes a decision to treat. Screening for LTBI starts with a careful medical and social history that identifies risks for exposure or development of disease. The CDC recommends “targeted testing” with TST or IGRA of persons with recent exposure or at high risk for reactivation disease (see Section I.e). Persons with a known history of a positive TST or IGRA, a history of treatment for LTBI, or active TB should not undergo repeated testing. B. Diagnosis. A TST or IGRA can provide the initial step for the diagnosis of LTBI (see Section IV.c.6). If the test result is positive, it is followed by clinical and laboratory assessment to rule out active TB. The diagnosis of LTBI can be made in the absence of clinical symptoms, physical examination, and laboratory or radiographic findings suggestive of active TB disease. Sputum smears and cultures should be sent for patients with respiratory symptoms or an abnormal CXR (ie, infiltrate or cavitary lung lesion). If a patient is referred with a positive TST or IGRA, the assessment follows the same steps, and a diagnosis of LTBI is made if active TB disease is not confirmed.