Facial granulomatous diseases: a study of four cases tested for the presence of Mycobacterium tuberculosis DNA using nested polymerase chain reaction.

The histopathologic diagnosis of cutaneous tuberculosis (CTB) is often troublesome, because there are several other entities (tuberculids, demodicidosis, granulomatous rosacea, and acne agminata) that may display granulomatous inflammation with caseation necrosis. The current study describes four cases of granulomatous disease of the face. The final diagnosis (assessed on the basis of the clinical response to therapy) was CTB in three cases and granulomatous rosacea in one case. Histologically, epithelioid granulomas were a constant feature; in one case of CTB, they displayed a palisading (granuloma annulare-like) arrangement. Caseation necrosis was a prominent feature only in the case of granulomatous rosacea. Routinely processed biopsy specimens were evaluated with nested polymerase chain reaction (nPCR) for Mycobacterium tuberculosis (MBT) DNA. The correlation between nPCR results and clinical outcome was less than optimal: in fact, one case showed an excellent clinical response to the antituberculous drug therapy despite the absence of MBT DNA amplification. In granulomatous diseases of the face, the importance of evaluating not only nPCR but the overall clinicopathologic picture so as to avoid diagnostic misinterpretations is emphasized.