Pleural tuberculosis

Tuberculosis (TB) can involve nearly any part of the body and can present in a number of ways clinically. Some presentations are classic and allow easy identification of the disease through standard procedure (pulmonary TB - sputum AFB smear/culture), while others require additional testing. Pleural TB is the third most common presentation of TB, following pulmonary and lymphatic involvement. This places pleural involvement at a rate of up to 20% of cases of TB in some studies. Pleural involvement is elevated in patient with HIV, specifically in those with higher CD4, which may point to the pathophysiology of this condition.

Pleural involvement can occur in the setting of primary or reactivation TB. Organisms gain access to the pleural space and stimulate an immune mediated response, particularly lymphocytes (Th1). This results in a delayed hypersensitivity reaction in the pleura. Pleural involvment can manifest as a simple effusion or empyema, which is much less common.

Clinical manifestations can develop quickly in this group of patients, where up to 30% present for medical attention within a week of onset. The most common clinical features include pleuritic chest pain, dyspnea and dry cough. Constitutional symptoms may also be present and are more common in HIV positive patients.

Typically, its said that patients with pleural TB are non-contagious and are unlikely to have positive sputums. that being said, extension into the pleura from parenchymal disease is one possible mechanism for effusion formation. CT scans of patients with pleural TB show up to 80% will have evidence of parenchymal involvement. Also, one study in patients with pleural TB found a 50% positive induced sputum culture rate in this population. Making it a test to be considered in all of these patients.

Pleural fluid analysis reveals several things. pH is rarely >7.4 in TB effusion. The cell count differential can initially show neutrophilic predominance, and will tend to shift to lymphocytic predominance thereafter. Eosinophilia is rare, and suggests an alternative diagnosis. AFB smear of pleural fluid is positive less than 10% of the time, with culture identifying TB in up to 30% of cases. The likelihood of identifying the organism increases in patients with HIV. Adenosine deaminase (ADA), an enzyme in the purine pathway associated with lymphocytes, has been found to be increased in pleural TB. The sensitivity and specificity of this test in patient with a high likelihood of TB is roughly 95% at certain levels. That being said, there are studies showing this can also be elevated in rheumatoid arthritis, lung malignancies and other pulmonary infections. PCR testing is useful, given that there are few bacteria present in the pleural fluid and this may allow magnification of the presence of infection. The Amplified Mycobacterium Tuberculosis Direct Test (AMTD) is a nucleic amplification test specifically for TB. This test is positive in 100% of patients with a positive culture, but only 60% in those who are pleural fluid culture negative. The gold standard historically has been pleural biopsy. Not only does it confirm TB, but it can help identify additional disease that may mimic a TB presentation (sarcoid, fungal infection etc). Thoracoscopy has been shown to be the overall most accurate means of diagnosing pleural TB, though it is also the most expensive.

See this review from CHEST for details:

Pleural TB diagnosis and management