Mucormycosis

Synonyms include zygomycosis and phycomycosis

Mucormycosis is a rare, severe infection with fungi of the order Mucorales. Rhizopus are the commonest species, with Rhizomucor, Cunninghamella, Saksenaea, and Apophysomyces species occurring less often.

These fungi are common environmental organisms that only cause disease when immunity is impaired. The spores grow, fungal hyphae invade blood vessels and produce tissue infarction. The result can be invasive, life-threatening disease. Severe infection of the facial sinuses may extend into the brain. Less common manifestations are pulmonary, cutaneous and gastrointestinal infections.

The condition is very rare but often unrecognised. Invasive fungal infections have always been a problem in the immunocompromised, typically aspergillosis and candidiasis, but mucormycosis has also increased in incidence over the last decade.¹

Risk factors

Impaired immunity from various causes:

• Poorly controlled diabetes mellitus, especially diabetic ketoacidosis²
• Steroid use³
• Neutropenia, especially with haematological malignancy⁴
• Renal insufficiency⁴
• Organ transplantation⁴
• Iron overload¹
• Burns³
• Broad-spectrum antibiotics¹

History

• There is usually a fulminant course with considerable tissue necrosis.
• Pyrexia is usual.
• In rhinocerebral disease there is unilateral, retro-orbital headache and nasal stuffiness progressing to a black discharge.
• Late symptoms from invasion of the orbital nerves and vessels include diplopia and visual field loss.
• These are late symptoms with a poor prognosis and usually are followed by reduced consciousness.
• Pulmonary mucormycosis presents nonspecifically with fever, dyspneoa, and cough.
• Cutaneous mucormycosis produces cellulitis that progresses to dermal necrosis and black eschar formation.
• Gastrointestinal mucormycosis occurs with severe malnutrition and may occur throughout the GI tract. Presentation is nonspecific, with abdominal pain, abdominal distension, nausea, and vomiting.

Examination

Only the signs of rhinocerebral mucormycosis are characteristic:

• Cellulitis of the orbit and face progresses with discharge of black pus from the palate and nose.
• Retro-orbital extension produces proptosis, chemosis, ophthalmoplegias and blindness.
• As the brain is involved the level of consciousness declines.

Pulmonary and gastrointestinal symptoms are non-specific but black, necrotic lesions of the skin indicate cutaneous disease.

• FBC
• Renal function (high doses of amphotericin B will be required and it is nephrotoxic)
• Diabetic control
• Ferritin and studies of iron status
• Imaging - both CT and MRI are useful to assess the skull, sinuses and brain (in general, CT is better for viewing bone and MRI gives better pictures of brain and soft tissues)
• CXR and chest CT (if chest disease is suspected)
• Abdominal CT (may show a mass by the gut)
• Tissue biopsy and microbiology (hyphae must be demonstrated to start treatment swiftly, culture is also required to determine the species but will take longer)

Drug

• Prompt administration of amphotericin B at high dose is essential. An adequate course lasts 4 to 6 weeks.
• Rectify any poor control of diabetes.
• Stop chemotherapy if it is causing neutropenia.
• Deferoximine should also be stopped.

Surgical

• Surgical debridement of any necrotic tissue is mandatory.
• In rhinocerebral disease, surgery includes drainage of the sinuses and may require excision of the eye, other orbital contents, and involved brain. Surgery may be quite destructive and need to be repeated.
• Pulmonary lesions can be excised if confined to a single lobe
• Full excision of cutaneous lesions is required.

There is massive invasion and infarction of local tissues.

Mucormycosis has a very high mortality rate of at least 50%. Mortality from pulmonary and gastrointestinal disease is even higher due to late diagnosis. In patients who survive rhinocerebral disease, treatment requires extensive and often disfiguring facial surgery. In an Italian study 65% of diagnoses were made post mortem⁵ although in many empirical antifungal treatment has already been given. Mortality in transplant patients can be 80%.