DIAGNOSIS OF PULMONARY TUBERCULOSIS
The chest radiograph is an invaluable tool in the diagnosis of pulmonary tuberculosis. Pulmonary tuberculosis typically demonstrates number of abnormalities on chest radiographs. Primary pulmonary tuberculosis most commonly reveals hilar lymphadenopathy, which may cause right middle lobe compression and atelectasis. Pulmonary infiltrates may be seen in primary tuberculosis, typically in the middle or lower lobes, but cavitary lesions are uncommon. Pleural effusions may also be present in cases of primary infection.In contrast, the radiographic appearance of reactivation tuberculosis is commonly that of disease of the upper lobes. Upper lobe infiltrates are routinely identified, and cavitation is common. Atypical presentations of reactivation tuberculosis include lower lobe infiltrates, pulmonary nodules, isolated pleural effusions, or isolated hilar lymphadenopathy. Rarely, chest radiographs may be normal in the patient with culture-proven tuberculosis, especially in immunosuppressed patients. In those with HIV, the incidence of active tuberculosis with a normal chest radiograph IS more common and may be close to 20% for patients with CD4 counts less than 200.Definitive diagnosis of tuberculosis relies on isolation of the organism from a clinical specimen. A patient with appropriate clinical findings and a chest radiograph suggestive of pulmonary tuberculosis should have sputum sent for mycobacterial stains and cultures. Sputum is best obtained by collecting the first sample expectorated by the patient in the morning. If the patient has evidence of pulmonary involvement by radiographs but continues to have non-diagnostic sputum samples, then bronchoscopy should be considered to confirm the diagnosis. The diagnostic yield of bronchoscopy may be greater than 90%.Distinguishing Mycobacterium tuberculosisirom Mycobacterium avium complex is important, particularly in the patient who is mycobacteria smear positive with cultures that are pending or negative. The development of nucleic acid amplification tests in the United States may achieve this goal. Some practitioners recommend the use of nucleic acid amplification test to rapidly diagnosis tuberculosis in patients who are mycobacterial smear positive. Nucleic acid amplification may also be used for patients with high clinical suspicion of pulmonary tuberculosis who remain smear-negative. Up to 50% of smear-negative cases that ultimately are culture positive can be rapidly diagnosed with these tests. The general use of nucleic acid amplification tests should be limited to these conditions. More advanced techniques for diagnosis of tuberculosis are likely to become available in the near future.*60/348/5*
