Mucormycosis
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Direct answer
Mucormycosis is an acute, angioinvasive infection caused by moulds of the order Mucorales, most often rhino-orbital-cerebral in people with uncontrolled diabetes and ketoacidosis. Its hyphae are broad, sparsely septate and branch at right angles, which separates them from Aspergillus. Treatment needs high-dose liposomal amphotericin B together with urgent surgical debridement, and delay in either worsens survival.
What you must remember
- Causative genera: Rhizopus, Mucor, Rhizomucor and Lichtheimia, all of the order Mucorales.
- Hyphal morphology: broad, ribbon-like, sparsely septate hyphae that branch at right angles, unlike the narrow septate hyphae of Aspergillus.
- Classic risk factor: uncontrolled diabetes with ketoacidosis, with high-dose corticosteroids, neutropenia, deferoxamine therapy, transplantation and haematological malignancy also raising risk.
- Rhino-orbital-cerebral disease: facial or sinus pain, nasal congestion and a black necrotic eschar on the turbinate or palate, with orbital spread causing ptosis and ophthalmoplegia.
- Diagnosis: tissue biopsy with KOH or calcofluor staining shows the hyphae, culture confirms the genus, and CT or MRI defines the extent.
- Galactomannan: not a reliable marker for Mucorales, because it is designed to detect Aspergillus.
- Treatment: high-dose liposomal amphotericin B with surgical debridement, and posaconazole or isavuconazole for step-down therapy.
A black eschar in a diabetic
A 55-year-old with poorly controlled diabetes and recent high-dose steroids presents with facial pain, nasal congestion and a black crust on the right nasal turbinate.
- Act urgently: rhino-orbital mucormycosis is a medical and surgical emergency, and any delay in starting therapy worsens the outcome.
- Image the extent: CT or MRI of the sinuses and orbit defines invasion of the orbit, palate or brain, which determines the surgical plan.
- Biopsy the margin: tissue from the eschar and the healthy margin is examined for broad, aseptate hyphae on KOH or calcofluor, and culture confirms the genus.
- Control the host: ketoacidosis, blood glucose and steroid doses are corrected, since these reversible drivers sustain the infection.
- Start high-dose amphotericin: liposomal amphotericin B is started immediately and continued until the disease is controlled.
- Debride early and repeatedly: surgical debridement removes necrotic tissue, and repeat operations are often needed to clear the disease.
The steps run together rather than in strict sequence, because imaging, biopsy and host correction all happen within the same days.
Where the exam tries to catch you
Mucormycosis questions test drug resistance, the morphology of the hyphae and the role of surgery.
- Trap: treating mucormycosis with voriconazole because it is an azole Correct: Mucorales are intrinsically resistant to voriconazole, so liposomal amphotericin B is the drug of choice.
- Trap: using serum galactomannan to diagnose mucormycosis Correct: galactomannan detects Aspergillus, so diagnosis rests on tissue biopsy showing broad, aseptate hyphae.
- Trap: choosing medical therapy alone for orbital disease Correct: early surgical debridement is combined with amphotericin B, and orbital or cerebral spread needs urgent surgical review.
Frequently asked questions
Why is voriconazole ineffective against mucormycosis?
Mucorales are intrinsically resistant to voriconazole, so the drug has no meaningful activity against them. Liposomal amphotericin B is therefore the mainstay of treatment. Posaconazole and isavuconazole are used later as step-down therapy once the disease is controlled.
What tissue findings distinguish mucormycosis from aspergillosis?
Mucorales show broad, ribbon-like, sparsely septate hyphae that branch at right angles, while Aspergillus shows narrow, septate hyphae with acute-angle branching. This difference is seen on KOH or calcofluor-stained tissue. It changes management, because it decides between an azole and amphotericin B.
Which conditions raise the risk of mucormycosis?
Uncontrolled diabetes with ketoacidosis is the classic risk factor for rhino-orbital-cerebral mucormycosis, and high-dose corticosteroids add to it. Neutropenia, deferoxamine therapy for iron overload, transplantation and haematological malignancy also increase risk. The disease was prominent in India during the 2021 COVID-19 surge.
What is the classic presentation of rhino-orbital-cerebral mucormycosis?
Rhino-orbital-cerebral mucormycosis presents with facial or sinus pain, nasal congestion and a black necrotic eschar on the nasal turbinate or palate. Orbital involvement causes periorbital swelling, ptosis and ophthalmoplegia. Spread to the brain produces neurological signs and needs urgent surgical review.