Rhizopus & Mucor
Both belong under the umbrella term, mucorales. These are bread moulds naturally on fruit and bread that we breathe in and out without much issue particularly if immunocompetent, but in some immunocompromised it causes rapidly fatal and progressive disease: mucormycosis. Due to the weakened immune system.
Spores released either land on skin or into blood via open wounds, then deposit tehre, invading local vessels, thrombosing them and cutting off supply. this rapidly leads to ischaemia and necrosis. Dead tissue.
Now for a Case Report. This one in Frontiers of Medicine. A 35 yo man with diabetes presents with a facial rash, that rapidly progresses to an eschar and ulcer. To note, there are graphic images in the link of his face.
This was initially associated with nasal discharge and epistaxis. Diagnosis was initially a peridontal infection which did not resolve with standard antibiotics for this, similarly he was next diagnosed with uncomplicated, stock standard cellulitis (usually staph or strep pyogenes caused). Both treatments failed.
eventually he was diagnosed with mucormycosis, but by then he had extensive damage to his face, the subcut tissues, muscles and facial bones. He also had significant weight loss, fevers, splenomegaly and thrombosis.
To muddy the waters, he was concurrently diagnosed with a T cell lymphoma but the authors also picked up Rhizopus.
What is Rhizopus? (also related to mucor, another mucorales) It's a fungi, more specifically an opportunistic pathogen commonly associated with diabetics (esp poorly controlled) and the immunocompromised (in particular solid organ transplants, see further case report in resources below, HIV, malnutrition, haematological malignancies - eg leukaemias).
Also associated with steroid use, form of immunosuppression so has been seen in severe COVID patients requiring dexamethasone (Rare though).
As a mould it likes the acidotic states in DKA and iron, so any iron overload states as well.
Why poorly controlled diabetics - it becomes an immunocormposed state in and of itself. The sugars suppress local inflammatory responses like neutrophil chemotaxis or phagocytosis etc. You can however, get chronic forms too. So don't rule it out if it's not wildly acute. These occur over weeks, slowly. Considering it's a mould, it's particularly "prolific" in hot weather and warm/hot climates.
Classically it is an infection that affects the face, parasinuses, nose and even the brain. You'll often hear the term rhinocerebral with it.
Consider it if you see discolouration around the face and definitely if you see a necrotic eschar. Actually, any black spots, fevers, rash, call ID urgently. Unsurprisingly, it is also called the black fungus.
Is also possible to have it affect the skin (particularly in IVDU and in burns), lungs and GI (more rare). IN lung involvement symptoms are typical for the organ - SOB, fevers, chest pain, haemoptysis. in GI: nausea/vomiting/GIB.
Thrombosis can occur as a complication as it invades the blood vessels.
In brain involvement from disseminated disease, expect confusion and altered state if not reduced GCS.
It's also been recently featured in the fungi podcast by the Curbsiders. Which is worth a listen.
It's filamentous and has hyphae.
You'll also hear the term mucormycosis = which just refers to the disease process that is rapidly fatal. Mortality is 30-70% of rhinocerebral cases, 90% in disseminated and 100% in AIDs --numbers from StatPearls. Survival improves with antifungals and surgery to 70%.
Early diagnosis and intervention is essential, as illustrated in the case report above. but is rare, so not infrequently missed.
It's also missed, as early symptoms are very non specific depending on how it affects the host. You can simply get lethargy, headache and eye pain. Blurry vision too, or simply epistaxis and rhinorrhoea.
Image from Wiki
Now that you know the clinical presentation and the increased risk groups to think of this diagnosis in,
How do you confirm your suspicions?
investigations:
It's associated with neutropaenic states and one hypothesis is acidosis in diabetics with poorly managed sugars (so really unwell). No serology (as compared to other bugs), would come up in fungal cultures and on tissue biopsy. key words on biopsy: Ribbon like hyphae branching at 90 degree angles.
Also from wiki, that suggests it looks like Moose antlers.
Pathologists will also note or look for necrosis and haemorrhage.
Blood cultures rarely pick up it, so consider it if they're unwell and culture negative.
On imaging - gold standard in rhino cerebral is MRI but CT is most accessible and fast. Looking for signs of blood vessel invasion and reverse halo or less specific halo sign.
Reverse halo per radiopaedia: ground glass within a consolidated crescent shape.
From radiopaedia:
Okay, this sounds both difficult to pick up and investigate. No magical PCR or serology.
Pro tip from stat pearls: just maintain a high index of suspicion in anyone with increased risk or risk factors. Biopsy tissue quickly particularly if necrosis is apparent. Early detection method is unsurprisngly CT --> we all seem to have a low threshold for this, but looking for hyperdensity (mucosal thickening) and erosion of the facial bones.
Also essential is the age old adage that most clinicians follow --> empirical therapy for the most common organisms, close monitoring/observations. then failing that, broaden the differentials and keep investigating or altering treatment quickly.
Treatment:
The strong stuff. Liposomal Amphotericin B for 4-6 weeks (the long duration) as it is highly invasive/progressive. Alternatives; itraconazole.
You may also hear of hyperbaric O2 therapy, which aids the neutrophils to kill the fungi. Also in stat pearls
Surgical debridement after antifungal therapy with washout depending on extent of damage.
Sources used for post:
Case reports, wiki and radiopaedia as above And largely Statpearls --> there is much more further detail and more to read on differentials and complications.
I'll try to use free resources as much as possible.
Another Case Reports of interest include: NEJM - lengthy one reminding all to consider this diagnosis in an unexplained rash in an immunocompromised host.
