Aggressive angioinvasive mold infection in diabetic ketoacidosis and immunocompromised hosts; rhinocerebral form is a surgical emergency.
Also known as: mucormycosis, zygomycosis, rhinocerebral mucormycosis, Rhizopus, Mucor, black fungus
Overview
Aggressive angioinvasive infection caused by molds of the order Mucorales, most commonly Rhizopus, Mucor, and Rhizomucor species. Characterized by rapid tissue invasion, vascular thrombosis, and infarction. Clinical forms include rhino-orbital-cerebral, pulmonary, cutaneous, gastrointestinal, and disseminated disease.
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Risk factors
- Diabetes mellitus, especially with ketoacidosis (acidosis impairs phagocytosis and frees iron)
- Hematologic malignancy with prolonged neutropenia
- Hematopoietic stem cell or solid organ transplantation
- Prolonged high-dose corticosteroid therapy
- Iron overload (hemochromatosis, multiple transfusions, deferoxamine therapy)
- Severe burns or trauma (cutaneous form)
- Voriconazole prophylaxis (which lacks Mucorales activity — breakthrough infections)
- COVID-19 with steroid use and uncontrolled diabetes
Pathophysiology
Inhalation, ingestion, or inoculation of sporangiospores. Mucorales hyphae invade blood vessels, causing thrombosis, infarction, and necrosis of surrounding tissue. Iron and hyperglycemia promote fungal growth; acidosis impairs neutrophil and macrophage function. The black eschar of rhinocerebral disease reflects vascular thrombosis and tissue necrosis.
Clinical presentation
Symptoms
- Rhino-orbital-cerebral: facial pain or numbness, headache, fever, nasal congestion with dark/bloody discharge, vision changes, ophthalmoplegia
- Pulmonary: fever, cough, chest pain, hemoptysis in immunocompromised host not responding to antibiotics or voriconazole
- Cutaneous: rapidly progressive necrotic skin lesion at site of trauma, surgery, burn, or IV catheter
- Gastrointestinal: abdominal pain, GI bleeding, perforation; mostly in malnourished infants or transplant patients
- Disseminated: multiorgan failure with CNS, lung, and skin involvement
Signs / physical exam
- Black eschar on palate, nasal turbinates, or skin (pathognomonic when present)
- Periorbital swelling, proptosis, chemosis, fixed dilated pupil, ophthalmoplegia
- Cranial nerve deficits (V, VII most commonly)
- Necrotic skin ulcer with dusky borders
- Hypotension and signs of sepsis in disseminated disease
Classic findings
Diabetic ketoacidosis patient with facial pain and a black eschar on the hard palate or nasal turbinate. Sinus CT showing bony erosion and orbital/intracranial extension. Broad non-septate ribbon-like hyphae with right-angle (90-degree) branching on tissue biopsy.
Differential diagnosis
- Invasive aspergillosis — Similar host risk factors; halo and air crescent signs more typical; septate hyphae with acute-angle branching on histopathology versus broad non-septate hyphae with right-angle branching of Mucorales; galactomannan and beta-D-glucan positive in aspergillosis, NEGATIVE in mucormycosis
- Bacterial sinusitis — Acute, responds to antibiotics; no necrosis or black eschar; lacks angioinvasion
- Cavernous sinus thrombosis (bacterial) — Periorbital edema, ophthalmoplegia; staph aureus often; consider mucormycosis if diabetes/immunocompromise
- Orbital cellulitis (bacterial) — Acute, responds to antibiotics; less necrosis; image to exclude fungal invasion if not improving
- Squamous cell carcinoma of sinuses — Chronic, infiltrative; biopsy distinguishes
- Pulmonary aspergillosis — Same host; imaging similar; tissue diagnosis distinguishes
Diagnostic workup
Diagnostic criteria
Definitive diagnosis: histopathologic identification of broad, ribbon-like non-septate or pauciseptate hyphae with right-angle branching, with or without positive fungal culture. Speed is critical — empirical therapy should not wait for culture results.
Labs
- Glucose, BMP with anion gap, ABG (for DKA assessment)
- CBC, LFTs
- Beta-D-glucan and galactomannan — typically NEGATIVE in mucormycosis (useful to differentiate from aspergillosis)
- Tissue biopsy for histopathology (GMS, PAS, Calcofluor white) and fungal culture is essential
- PCR and DNA sequencing of tissue (specialized centers)
- Blood cultures rarely positive even in disseminated disease
Imaging
- Sinus CT/MRI with contrast: mucosal thickening, bony erosion, orbital extension, cavernous sinus involvement, intracranial extension
- Chest CT for pulmonary form: nodules, cavitation, reverse halo sign (more specific than halo sign for mucor), pleural effusion
- MRI brain for CNS involvement
- Vascular imaging if internal carotid artery thrombosis suspected
Treatment
First-line
- Liposomal amphotericin B 5-10 mg/kg/day IV — first-line antifungal; start immediately on clinical suspicion
- Aggressive surgical debridement of all necrotic tissue (often disfiguring but life-saving) — repeated debridements typically required
- Reverse predisposing conditions: correct DKA and hyperglycemia, reduce or eliminate corticosteroids, discontinue deferoxamine, restore neutrophils with G-CSF if possible
- Step-down therapy after clinical and radiographic response: isavuconazole 200 mg PO daily OR posaconazole delayed-release 300 mg PO daily for prolonged duration (months)
- Treatment duration is highly individualized — continue until clinical, radiographic, and ideally mycologic resolution
Second-line / adjunct
- Posaconazole or isavuconazole alone if amphotericin B intolerance (less effective as monotherapy in induction)
- Combination amphotericin B + echinocandin or amphotericin B + azole has been used but lacks strong evidence
- Hyperbaric oxygen therapy has anecdotal support, not standard
- Iron chelation with deferasirox is INVESTIGATIONAL and not currently recommended outside trials
Complications
- Cavernous sinus thrombosis, internal carotid artery thrombosis, stroke
- Cranial nerve deficits, blindness, disfigurement after debridement
- Brain abscess and meningitis
- Massive hemoptysis (pulmonary form)
- Bowel perforation and peritonitis (GI form)
- Amphotericin B nephrotoxicity, electrolyte wasting, infusion reactions
- High overall mortality — 40-80% even with aggressive therapy
PANCE pearls
- Mucormycosis is a SURGICAL emergency — antifungals alone rarely cure invasive disease. Repeated debridement is essential.
- Black eschar on the palate or nasal mucosa in a patient with DKA is mucormycosis until proven otherwise.
- Beta-D-glucan and galactomannan are NEGATIVE in mucormycosis — useful to distinguish from invasive aspergillosis.
- Voriconazole has NO activity against Mucorales — breakthrough mucormycosis in patients on voriconazole prophylaxis is a recognized syndrome.
- On histology: broad, ribbon-like, non-septate (or rarely septate) hyphae with 90-degree branching versus narrow, septate, 45-degree branching of Aspergillus.
References
- ECMM/ISHAM 2019 — Global guideline for the diagnosis and management of mucormycosis (Cornely et al., Lancet Infect Dis 2019)
- IDSA — IDSA guidance on diagnosis and management of invasive mold infections including mucormycosis
- CDC — CDC — Mucormycosis: clinical features, risk factors, and treatment overview
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