Friday, July 22, 2005

Latent TB or not latent TB?

Guidelines for handling a positive PPD is to get an xray to see if it is abnormal. Presumably, this is to rule out ctive TB so you would then treat with 4 drugs instead of the INH for 6 months. But what is an abnormal xray? A cavitary lesion is obvious. What about apical scarring? Would you treat this as latent? What about a nodule? If your answer is that you would treat those as latent, then the utility of even obtaining a cxr is less; how many patients with active TB have no clinical signs of active TB? If your answer is that you would treat the +ppd apical scar patient as active, then you need to consider that apical scarring may represent previous exposure to TB but the body "dealt with it" and the result is some scarring. Isn't tht therefore considered latent?

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Baleeiro said...

Actually, there is another aspect to the scar question. First, if there is only apical scarring, no infiltrate, no cough and no symptoms, you would only treat as LTBI.
The significance of the scarring is that there is a much higher risk for re-activation than just a +PPD with normal CxR. It is important to point that out to someone who may be less inclined to take INH; and to help decide if someone healthy with no exposure who has a borderline PPD because of work for instance should be treated.