Subcutaneous Mycoses

Many are dematiaceous, aka, pigmented fungi; it is thought that the melanin in their cells contributes to virulence. Morphology: many are dimorphic, which means they exist in both hyphal and yeast forms. Transmission: they reside in soil, on plants, and decaying vegetation; trauma to the skin introduces pathogenic fungi to the underlying tissues. Localized infections: infections tend to occur on the extremities, especially the feet and hands, which are likely to be inoculated during gardening or field work. Lesions: chronic, granulomatous lesions in the skin and deeper tissue. Often, histopathologic samples will show Splendore-Heoppli phenomenon, aka, asteroid bodies, which are characterized by eosinophilic materials radiating from the microorganisms. The initial lesion occurs at the site of inoculation, for example, in the skin of the feet, then spreads to deeper tissues, which can include the lymphatics, muscles, and connective tissues. Infection can disseminate to other organs, but this is rare. Treatment: long-term antifungals can be used to treat some subcutaneous mycoses. "Rose Gardener's Disease": many individuals are inoculated via rose thorns. The fungi most often responsible are members of the Sporothrix schenckii complex. Mycosis manifests as linear cutaneous nodules and ulcers that begin at the site of inoculation and travel along the path of the draining lymphatics. In some patients, the lesions will become suppurative; the discharged pus contains fungi that is useful for diagnostic purposes. Chromomycosis is caused by a variety of fungi: Fonsecae, Cladosporium, Phialophora, etc. Histopathologic samples show characteristic Medlar bodies (aka, sclerotic bodies or muriform cells). Medlar bodies are cells with transverse septa and thick, pigmented cell walls; some liken them to copper pennies. Chromoblastomycosis produces slowly developing, chronic lesions that can cause progressive tissue fibrosis. Lesion morphology varies; for example, some patients have warty or "cauliflower-like" nodules, while others develop plaques with central scarring. Mild cases where warty nodules are involved may be cured by excision. However, excision is not practical in patients with extensive lesions, as we see in the example of plaques; thus, long-term antifungals are the preferred treatment in such cases. Madura foot (Maduramycosis) is caused by Madurella mycetomatis and other fungi. Because mycetoma is also caused by bacteria, it's important to culture samples from the patient to rule out actinomycete mycetoma, which requires a different intervention. Eumycotic mycetoma is characterized by painless nodules that progress to ulcers; the ulcers discharge fluid and granules. The granules comprise the fungal hyphae, and their color is indicative of the microorganism type M. mycetomatis granules are dark brownish-black. Eumycotic mycetoma is a chronic and progressive condition, and new sinuses form as older sinuses heal. The draining sinuses produce swelling and tissue deformity; infection can ultimately invade and destroy deeper tissues. Unfortunately, eumycotic mycetoma often responds poorly to antifungal treatments, so amputation is often necessary to prevent further destruction. Conidiobolus coronatus Conidiobolomycosis most commonly affects adults. Inhalation produces infection in the nasal and paranasal sinuses; swelling and deformity of the nose and upper lip can be quite dramatic, though relatively painless. Basidiobolus ranarum Basidiobolomycosis more commonly affects male children. Produces "rubbery" dark lesions on the buttocks, thighs, and shoulders; gastrointestinal involvement is possible, though rare. Various species: Exophiala, Bipolaris, Curvalaria, etc. Histopathologic samples are characterized by irregular hyphae. Infection produces slow growing cysts, or, sometimes, plaques.