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Blastomycosis causing laryngeal leukoplakia

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Blastomyces dermatitidis, a soil saprobe found endemically in regions of the Mississippi and Ohio River Valleys, may rarely cause laryngeal leukoplakia. The inflammatory infiltrate that accompanies Blastomyces is usually granulomatous with a conspicuous mix of neutrophilic inflammation. Occasionally the negative image of the yeast can be identified on H&E stain. A well-recognized pitfall is to mistake the pseudoepitheliomatous hyperplasia overlying the inflammation for well-differentiated squamous cell carcinoma. It is important to examine the submucosa of such biopsies for granulomas and evidence of infectious etiologies. Special stains are required for diagnosis. Yeast forms for Blastomyces may be as large as 16-20 micrometers and bud with a broad base.