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Diagnosis and Treatment of Fungal Infections

Diagnosis and Treatment of Fungal Infections

John E. Bennett

MYCOLOGY FUNDAMENTALS

Fungi can appear microscopically as either rounded, budding forms (yeastlike organisms) or hyphae (molds). Yeastlike colonies are smooth, while mold colonies are fuzzy; fungi that grow as yeasts include species of Candida and Cryptococcus, while fungi that grow as molds include species of Aspergillus, Rhizopus, and dermatophytes (ringworm fungi). The fungi that cause histoplasmosis, blastomycosis, sporotrichosis, coccidioidomycosis, and paracoccidioidomycosis are called dimorphic (“having two forms”) because they are spherical in tissue but grow like molds when cultured at room temperature. Candida species other than Candida glabrata appear in tissue as both budding yeasts and tubular elements called pseudohyphae. Pseudohyphae, unlike true hyphae, have constrictions in the cell wall where septa are located and have septa at branching points. Pneumocystis is closer to fungi than to parasites by ribosomal sequences. Because the drugs used to treat Pneumocystis pneumonia are also used to treat parasitic or bacterial infections, those drugs will not be discussed in this chapter.

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Dermatitis

Dermatitis

Dermatitis is a nonspecific inflammatory response of the skin to a combination of exogenous and endogenous factors. It is manifest as an itchy, erythematous, and sometimes scaly rash. In the acute stage, there may be weeping, crusting and blisters. Histologically there is spongiosis (intercellular oedema) and superficial inflammation. There is not a clear distinction between dermatitis and eczema, and the two terms are interchangeable.

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Dermatological emergencies

Dermatological emergencies

There are several conditions that can be classed as dermatological emergencies because of their severity and acute nature. Others can be classed as emergencies because it is essential to get a definitive diagnosis quickly so that correct treatment can be started immediately to prevent complications such as scarring.

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Cutaneous vasculitis

Cutaneous vasculitis

The classical clinical lesion of vasculitis is palpable purpura, most commonly of the legs. Urticaria, erythematous swellings, vesicles, pustules, bullae, erythematous macules, papules and plaques can, however, be seen in the cutaneous eruption. Vasculitis is usually defined histologically as a process that involves the destruction of blood vessels, most often with cellular infiltrate of the vessel walls, proliferation of the intima, fibrinoid change in the vessel walls and narrowing or occlusion of the vessel lumen. Clinical manifestations vary with the site, size and depth of the vessel involved.

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