This preschooler had a one-day history of a necrotic lesion on the top of the right hand. She had a history of sideroblastic anemia for which she received a bone marrow transplant 1 year ago. While on chronic immunosuppression she was admitted to the hospital 2 weeks ago for evaluation and treatment of fever. Although there was no reported history of hand trauma, the site corresponded to previous intravenous access sites. Fungi of the phylum Zygomycota cause zygomycosis, also called mucormycosis. The genera most commonly responsible are Rhizopus, Mucor, and Absidia. These “bread molds” are present in decaying fruits and vegetables, seeds, soil, animal excreta, and other carbohydrate-rich substrates. They have also been detected in 22 percent of air samples from 2 hospital wards, compared to only 5 percent of samples from outside air. Although skin lesions are most commonly caused by inhalation of the mold with secondary dissemination to the skin., primary cutaneous zygomycosis can also occur with direct inoculation of the skin (particularly at sites of trauma such as IV sites) and may disseminate hematogenously in immunocompromised hosts.
Both zygomycosis and aspergillosis are opportunistic infections that characteristically cause necrotic skin lesions as a result of invasion of blood vessels. They typically occur in immunocompromised hosts, including bone marrow or organ transplant patients on chronic immunosuppression. It is necessary to differentiate between zygomycosis and aspergillosis because treatment of zygomycosis requires extensive surgical debridement of necrotic tissue, as the thrombotic properties of zygomycosis prevent adequate penetration of antifungal medications into infected tissue.
These two organisms can be differentiated histologically. Aspergillus displays septate hyphae with 45-degree branching, while Rhizopus and Mucor display non-septate twisted hypae with 90-degree branching. Rapid diagnosis is imperative to prevent further tissue necrosis and potentially fatal dissemination. This can be accomplished by tissue biopsy and H&E staining of frozen tissue. KOH touch preps or scrapings can also be attempted. Separate tissue samples should also be sent for permanent sections for H&E and special stains and for tissue culture. Macroscopic cultures of zycomycosis show ‘wooly’ colonies in most instances, while those of Aspergillus show khaki green (flavus) or blue-green (fumigatus) colonies with a rim of white to yellow color.
While azole antifungals may be effective for aspergillosis, Amphotericin B appears to be the only antifungal with potential efficacy for zygomycosis. Hyperbaric oxygen and potassium iodide may also be useful. In addition, granulocyte-macrophage colony stimulating factor (GM-CSF) therapy may be a useful adjunctive therapy for patients with diminished neutrophil counts.
necrotic ulcer with surrounding edema, erythema, and purpura