Monday, August 29, 2005
What is active TB?
I will post a case later, but in the meantime, Mike's post on the PPD brings up a good point. What is the radiographic definition of active TB? Is adenopathy active? How about multiple tiny nodules? If you say yes to the latter, how do you know those nodules don't represent non-specific ditzles (like they usually do). If you look up anything on latent vs active, no one (that I could find) actually defines what "active" means. Obviously a cavitary lesion would be one definition, but beyond that it gets very silent out there...
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The ATS actually addresses that on their statement on LTBI. Certain patterns are consistent with old TB and carry different individual risk factors: "In persons with LTBI, the chest radiograph is usually normal, although it may show abnormalities suggestive of prior TB. Previous, healed TB can produce various radiographic findings that usually differ from those associated with active TB. Dense pulmonary nodules, with or without visible calcification, may be seen in the hilar area or upper lobes. Smaller nodules, with or without fibrotic scars, are often seen in the upper lobes, and upper-lobe volume loss often accompanies these scars. Nodules and fibrotic lesions of previous, healed TB have well-demarcated, sharp margins and are often described as "hard." Bronchiectasis of the upper lobes is a non-specific finding that sometimes occurs from previous pulmonary TB. Pleural scarring may be caused by prior TB but is more commonly caused by trauma or other infections. Nodules and fibrotic scars may contain slowly multiplying tubercle bacilli with substantial potential for future progression to active TB [64]. Conversely, calcified nodular lesions (calcified granulomas) and apical or basal pleural thickening pose a lower risk for future progression to active TB."
This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, July 1999. Published by The American Thoracic Society, Am J Respir Crit Care Med 2000; 161:S221.
They (the ATS consensus) suggests the following as far as CXR eval: "If chest radiographs are normal and no symptoms consistent with active TB are present, tuberculin-positive persons may be candidates for treatment of LTBI. If radiographic or clinical findings are consistent with pulmonary or extrapulmonary TB, further studies (eg, medical evaluation, bacteriologic examinations, and a comparison of the current and old chest radiographs) should be done to determine if treatment for active TB is indicated."
This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, July 1999. Published by The American Thoracic Society, Am J Respir Crit Care Med 2000; 161:S221.
So basically, infiltrates are obviously suspicious. Scars are just evidence of old disease and adenopathy and nodules ought to be compared to old films if possible and weighed in the context of presence/absence of symptoms.
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