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.
Epidemiology
Uncommon but devastating. Mortality 40-80% even with treatment. Outbreaks reported in association with COVID-19, particularly in India during the second wave (CAM — COVID-associated mucormycosis). Rhinocerebral form most common in diabetic ketoacidosis; pulmonary form predominates in hematologic malignancy and transplant.
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Question 1Infectious DiseaseMedium
A 55-year-old woman with poorly controlled diabetes (HbA1c 11.2%) has right facial pain, eye proptosis, and nasal discharge. CT shows right maxillary sinus opacification with bony erosion and orbital extension. KOH preparation of sinus scraping shows broad non-septate hyphae with right-angle branching. Which of the following is the most likely diagnosis?
AMucormycosis
BCandidal sinusitis
CInvasive aspergillosis
DBacterial sinusitis
Reveal answer & full explanation
Correct answer: A — Mucormycosis
AMucormycosis✓
BCandidal sinusitis
CInvasive aspergillosis
DBacterial sinusitis
Why Mucormycosis is correct
Mucormycosis is caused most commonly by Rhizopus and Mucor; major risk factors include uncontrolled diabetes with ketoacidosis (acidic pH releases iron from transferrin, fueling fungal growth), hematologic malignancy, and transplant.
KOH preparation shows broad (6-25 micron) aseptate hyphae with wide-angle (90-degree) branching — exactly as described — distinguishing Mucorales from Aspergillus.
Angioinvasion leads to thrombosis, rapidly progressive necrosis, and black eschar with the orbital extension seen here.
Why the others are wrong
Candidal sinusitis — Candida forms narrow, septate pseudohyphae or true hyphae, not the broad aseptate wide-angle hyphae shown (confused-with fungal morphology).
Invasive aspergillosis — produces septate hyphae with 45-degree acute-angle branching on KOH, not broad aseptate wide-angle hyphae (confused-with mold morphology).
Bacterial sinusitis — does not produce hyphae on KOH and does not cause the angioinvasive bony erosion and orbital extension described (anchoring).
Additional high-yield points
Treatment: (1) aggressive surgical debridement (mainstay of cure); (2) liposomal amphotericin B 5-10 mg/kg/day; (3) isavuconazole as an alternative or in combination; (4) control diabetes; (5) reduce immunosuppression.
Voriconazole must be AVOIDED — all Mucorales have intrinsic resistance to voriconazole.
Question 2Infectious DiseaseMedium
A 54-year-old man with poorly controlled type 2 diabetes presents with two days of worsening right-sided facial pain, headache, and bloody nasal discharge. He was recently treated for a presumed sinus infection without improvement. Temperature is 38.4°C (101.1°F), and he is lethargic. Fingerstick glucose is 480 mg/dL, serum bicarbonate is 12 mEq/L, and there are large serum ketones. Examination shows right periorbital swelling, proptosis, and a fixed dilated pupil. A black eschar is visible on the right nasal turbinate and hard palate. Which of the following is the most likely diagnosis?
ARhino-orbital mucormycosis
BSinonasal squamous carcinoma
CBacterial orbital cellulitis
DInvasive sinus aspergillosis
Reveal answer & full explanation
Correct answer: A — Rhino-orbital mucormycosis
ARhino-orbital mucormycosis✓
BSinonasal squamous carcinoma
CBacterial orbital cellulitis
DInvasive sinus aspergillosis
Why Rhino-orbital mucormycosis is correct
Rhino-orbital-cerebral mucormycosis is the classic presentation in a patient with diabetic ketoacidosis: acidosis impairs phagocytosis and frees iron, and hyperglycemia plus available iron promote rapid growth of Mucorales molds.
The Mucorales are angioinvasive, causing vascular thrombosis, tissue infarction, and necrosis — producing the pathognomonic black eschar on the nasal turbinate or hard palate.
Proptosis, ophthalmoplegia, and a fixed dilated pupil reflect orbital and cavernous sinus extension, a surgical emergency requiring immediate liposomal amphotericin B and aggressive debridement.
Why the others are wrong
Bacterial orbital cellulitis causes periorbital swelling and proptosis but is not angioinvasive and does not produce a necrotic black eschar; it typically responds to antibiotics, which failed here.
Invasive sinus aspergillosis shares the immunocompromised host and angioinvasion, but galactomannan and beta-D-glucan are positive (negative in mucormycosis), and a palatal black eschar in a DKA patient points to Mucorales (broad non-septate hyphae with 90-degree branching) rather than Aspergillus (septate, 45-degree branching).
Sinonasal squamous carcinoma is a chronic, slowly infiltrative process diagnosed by biopsy; it does not cause acute fever, rapid necrosis, and a black eschar over days.
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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)
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
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
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
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