Tuberculous Pleural Effusion
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Direct answer
Tuberculous pleural effusion is a lymphocyte-predominant exudate that develops from a hypersensitivity reaction to tubercle bacilli in the pleural space, most often in young adults. Adenosine deaminase in the fluid is typically raised, while the bacilli are so scanty that culture is low yield. Pleural biopsy showing caseating granulomas is the most useful diagnostic test. Standard anti-tubercular therapy for six months is the cure, and drainage only relieves symptoms.
What you must remember
- Fluid type: an exudate with lymphocyte predominance, with normal pH and glucose in most cases.
- Adenosine deaminase: raised ADA, commonly above about 40 U/L, supports tuberculosis, though the cutoff varies between studies.
- Culture yield: low, because the disease is hypersensitivity-driven and bacilli are scanty, so a negative culture does not exclude it.
- Pleural biopsy: closed-needle biopsy showing caseating granulomas gives the best yield, and thoracoscopic biopsy is used when it is not diagnostic.
- Pathogenesis: delayed hypersensitivity to tubercle antigens, and the chest film often shows no parenchymal lesion.
- Treatment: standard anti-tubercular therapy for six months, with corticosteroids sometimes added in large effusions after specialist advice.
A young man with a unilateral effusion and evening fever
A 26-year-old man from a high-prevalence area has two weeks of fever, night sweats and right-sided pleuritic pain. His chest film shows a moderate right effusion, and the fluid is a lymphocyte-rich exudate.
Tuberculous pleural effusion should be considered in any young adult with a lymphocytic exudate and constitutional symptoms. The diagnosis is built step by step, and each test narrows the differential.
- Confirm an exudate: Protein, lactate dehydrogenase and cell count separate an exudate from a transudate, and a lymphocytic exudate narrows the differential.
- Measure adenosine deaminase: A raised value supports tuberculosis, especially in endemic settings, and a normal value makes it less likely.
- Send fluid for microbiology: Acid-fast smear, culture and molecular testing are sent, though yield is low, so a negative result never excludes the disease.
- Biopsy the pleura: Closed-needle biopsy showing caseating granulomas is the most useful test, and thoracoscopic biopsy is used if the closed biopsy is non-diagnostic.
- Exclude malignancy: Cytology and pleural biopsy look for lymphoma or mesothelioma, since a lymphocytic effusion can also be malignant.
- Start treatment: Standard anti-tubercular therapy is given once tuberculosis is likely, with follow-up of symptoms and the chest film after the effusion resolves.
Where the exam tests the pleural differential
The exam tests whether you over-read one test or miss the step that settles the diagnosis.
- Trap: trusting a negative culture to exclude tuberculosis Correct: bacilli are scanty, so culture is low yield, and granulomas on biopsy are more useful.
- Trap: using adenosine deaminase alone as a diagnosis Correct: lymphoma, empyema and rheumatoid pleurisy can also raise it, so it supports rather than confirms the diagnosis.
- Trap: assuming a pleural effusion means lung tuberculosis Correct: the effusion is a hypersensitivity response, and the lung parenchyma may look normal on the chest film.
- Trap: draining the effusion as definitive treatment Correct: drainage relieves symptoms, but the cure comes from anti-tubercular therapy.
Frequently asked questions
Which fluid finding suggests tuberculous pleural effusion?
A lymphocyte-predominant exudate with raised adenosine deaminase suggests tuberculous pleural effusion, especially in a young adult from an endemic area. Pleural biopsy showing caseating granulomas is the most useful confirmatory finding.
Why is pleural fluid culture low yield in tuberculous effusion?
Pleural fluid culture is low yield in tuberculous effusion because the disease is driven by hypersensitivity, so mycobacteria are very scanty in the pleural space. A negative culture therefore does not exclude tuberculous pleurisy, and pleural biopsy is needed.
Does adenosine deaminase confirm tuberculous pleural effusion?
Adenosine deaminase supports the diagnosis of tuberculous pleural effusion, and values above about 40 U/L are commonly used, though the cutoff varies. Lymphoma, empyema and rheumatoid pleurisy can also raise adenosine deaminase, so it supports rather than confirms the diagnosis.
Are corticosteroids used in tuberculous pleural effusion?
Corticosteroids are sometimes added to anti-tubercular therapy in large tuberculous effusions to relieve symptoms. They have not been shown to prevent residual pleural thickening, so the decision is taken with specialist advice rather than as routine care.