Mucormycosis is the common name given to several different diseases caused by fungi of the order Mucorales. It is also called zygomycosis after the class Zygomycetes, which are molds that grow in the environment and in tissue as hyphal forms. Rhizopus species are the most commonly isolated agents of mucormycosis, followed by Rhizomucor and Cunninghamella.

Mucormycosis is mostly limited to people with severe immunocompromise, diabetes mellitus, or trauma. Solid-organ and hematopoietic stem-cell transplant recipients represent a growing population at risk. More than half of patients have rhinocerebral disease; approximately 10% have pulmonary, cutaneous, or disseminated disease; and 2% have kidney or gastrointestinal involvement. Three-quarters of transplant patients with mucormycosis also had diabetes or had received antirejection therapy. It is rarely seen in immunocompetent hosts.

Most commonly, the fungus gains entry to the body through the respiratory tract and is inhaled from the nasal turbinates. In the case of primary cutaneous mucormycosis, spores are introduced directly into abraded skin. They then proliferate and can invade more widely. Once the fungus begins to grow, the hyphae invade tissue and have a special affinity for blood vessels. Direct penetration and growth through the blood-vessel wall explain the propensity for thrombosis and tissue necrosis, two major hallmarks of the histopathology of mucormycosis.

Rhinocerebralmucormycosis is most often found in patients with diabetes mellitus, particularly in the presence of acidosis, and in patients with leukemia who have been neutropenic for long periods and who have been receiving broad-spectrum antibacterial drugs. Patients complain of facial pain and/or headache, and fever and orbital cellulitis occur. Invasion often involves the palate and perioral tissues, first with erythema and then the development of ulceration (where it can mimic a herpetic lesion), which may turn black, reflecting the characteristic tissue necrosis. It is important to consider the possibility of mucormycosis before the development of the necrotic ulcer. With invasion of the orbit loss of extraocular muscle function, proptosis, and
marked swelling of the conjunctiva become evident. Loss of visionmay result from thrombosis of the retinal artery and the development of cranial nerve dysfunction is manifested by ptosis and pupillary dilatation, which represents a serious prognostic event. Cerebral abscess, cavernous sinus, and internal carotid artery thrombosis are additional complications.