Deep fungal infections comprise two distinct groups of conditions, the subcutaneous and systemic mycoses. Neither are common, and the subcutaneous mycoses, with some exceptions, are largely confined to the tropics and subtropics. In recent years, the systemic mycoses have become important opportunistic infectious complications in immunocompromised patients, including those with acquired immunodeficiency syndrome (AIDS) and patients receiving treatment for malignancies. They also include a group of primary respiratory infections, such as histoplasmosis and coccidioidomycosis, which may affect otherwise healthy individuals and those with underlying illness. The fungi that cause these respiratory infections are usually dimorphic or exist in a different morphologic phase (e.g., yeast or mold) at different stages of their life cycle.
Patients with subcutaneous fungal infections often present to a physician with signs of skin involvement. By contrast, patients with systemic mycoses only occasionally have skin lesions, either following direct involvement of the skin as a portal of entry or after dissemination from a deep focus of infection. There are a number of excellent texts about fungi and the diseases they cause.1–4
Treatment of these conditions remains difficult in many cases, although there is now a wide range of antifungal drugs with different modes of action.
Subcutaneous Mycoses at a Glance
- Are usually sporadic.
- Are contracted in the tropics and subtropics.
- May cause chronic disability.
- Are best diagnosed by histopathology, except for sporotrichosis.
- Often require months of successful antifungal treatment.
The subcutaneous mycoses, or mycoses of implantation, are infections caused by fungi that have been introduced directly into the dermis or subcutaneous tissue through a penetrating injury, such as a thorn prick. Although many are tropical infections, others, such as sporotrichosis, are also prevalent in temperate climates; any of these infections may present as an imported disease in a patient who has originated from an endemic area, sometimes after a lapse of many years. The most common subcutaneous mycoses are sporotrichosis, mycetoma, and chromoblastomycosis. Rarer infections include lobomycosis and subcutaneous zygomycosis.
Sporotrichosis is a subcutaneous or systemic fungal infection caused by the dimorphic fungus Sporothrix schenckii.5,6 The fungus occurs in the natural environment, presumably in mold (cells growing in a chain) form, but develops as a yeast (cells growing as single cells) in infections. The most frequent site of this infection is the dermis or subcutis. There is also a systemic form of sporotrichosis whose clinical features range from pulmonary infection to arthritis or meningitis. One important characteristic of the diagnosis of cutaneous lesions is the scarcity of organisms in tissue, making confirmation of the diagnosis by microscopy potentially difficult.6 Sometimes in tissue, fungal cells are surrounded by an eosinophilic refractile fringe, the asteroid body, that is a characteristic of the organism, although a similar phenomenon may occur with other infectious organisms (e.g., Schistosome eggs).