Abstract:

Cutaneous mucormycosis is most commonly caused by hematogenous spread of Mucor in immunocompromised patients. Skin biopsy is characterized by a deep fungal infection with frequent angioinvasion. The fungal hyphae can usually be identified on hematoxylin-eosin stain. Here we report a case of cutaneous angioinvasive mucormycosis in which the fungi were visualized on direct immunofluorescence. A 57-year-old patient with myelodysplastic syndrome status-post allogenic stem cell transplantation was admitted due to concern for graft-versus-host disease. During the hospital course, he developed painful and palpable dark red to violaceous retiform purpura on the upper and lower extremities unassociated with trauma. Punch biopsy of a representative lesion revealed numerous ribbon-like, non-septate, angioinvasive hyphae in the dermis consistent with mucormycosis. Direct immunofluorescence performed on a concurrent biopsy to exclude immune complex vasculitis demonstrated smooth IgG, IgA, and C3 deposition on the ribbon-like hyphal structures, compatible with coating of Mucor with these antibodies. Tissue culture subsequently confirmed Mucor species. To our knowledge, this is the first report of cutaneous mucormycosis visualized on direct immunofluorescence. Literature on antibody-coated microorganisms is largely limited to the examination of urinary sediments by direct immunofluorescence, in which a positive result would indicate local production of urinary antibodies in the kidney and support a diagnosis of bacterial or fungal pyelonephritis over a lower urinary tract infection. The urinary pathogens were most frequently coated with IgG and IgA antibodies, similar to our observations. Although mucormycosis was readily diagnosable on routine light microscopy in our case, recognition of the phenomenon of antibody-coated fungi can be crucial when the invasive fungi are sparse and only present in the specimen submitted for direct immunofluorescence.

Financial Disclosure:
No current or relevant financial relationships exist.

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Ashley Brent, MD