DermDx: Painful, Erythematous Sores on Arm

The patient is diagnosed with mucormycosis, a severe and potentially fatal infection caused by molds belonging to the order Mucorales. People become infected with mucormycosis by coming into contact with the fungal spores from Rhizopus, Apophysomyces, Mucor, or Lichtheimia species.1...

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The patient is diagnosed with mucormycosis, a severe and potentially fatal infection caused by molds belonging to the order Mucorales. People become infected with mucormycosis by coming into contact with the fungal spores from Rhizopus, Apophysomyces, Mucor, or Lichtheimia species.¹

While typically harmless in healthy hosts, these molds cause deadly infections in those with compromised immunity from hematologic malignancies or during treatment following bone marrow transplant.^2,3 Risk factors for cutaneous mucormycosis include uncontrolled diabetes with metabolic ketoacidosis, burn injuries, and hemochromatosis treated with deferoxamine.^1-6

Primary cutaneous mucormycosis presents with a chronic disease course, while secondary cutaneous mucormycosis, such as in this patient with leukopenia, follows an acute course and is associated with higher mortality.² Secondary cutaneous mucormycosis may present with edematous erythematous plaques that rapidly progress. These plaques form ulcers with eschar and adjacent erythema.² The lesions may arise at the site of an injury; however, a preexisting injury is not always noted.

There are a number of conditions that may mimic mucormycosis. Tularemia, otherwise known as Rabbit Fever, is caused by Francisella tularensis. The disease is preceded by contact with infected animals or invertebrate vectors. The infection may have an indolent course or an abrupt onset with nonspecific symptoms, including fever, chills, anorexia, and malaise. Classically, the fever will abate and return a few days later. The cutaneous lesion will present as an ulcer at the site of inoculation with painful local lymphadenopathy. ⁷

Pseudomonas aeruginosa is the pathogen responsible for most cases of ecthyma gangrenosum. This infection occurs most commonly in neutropenic patients, particularly after chemotherapy, and is consistently associated with bacteremia. While edematous plaques that progress to ulceronecrotic lesions are also seen in ecthyma gangrenosum, the most common locations are anogenital or axillary, and lesions are solitary or few in number. ⁸

Cutaneous anthrax, or Wool Sorter Disease, is caused by Bacillus anthracis. Spores in contaminated animal products such as wool, hide, or hair, enter the skin through a cut or scrape. The morphology of anthrax also progresses from erythema with marked edema and vesiculation to an ulcer with eschar, but history and exposure are distinct from mucormycosis. ⁹

Early detection and treatment of cutaneous mucormycosis correlates with better patient outcomes. The infection usually has a nonspecific initial presentation; biopsy for frozen sections or potassium hydroxide (KOH) staining are usually enough for diagnosis. Large, thin-walled aseptate or hyposeptate hyphae with irregular right-angle branching can be seen under microscope. Scrapings for KOH examination should be collected from the periphery of the lesion.^2,3

The mortality rate of patients with cutaneous mucormycosis depends on the spread of the disease. Localized cutaneous mucormycosis carries a mortality rate between 4% to 10%, while disseminated disease carries a mortality rate between 26% to 50%.² The overall mortality rate has decreased drastically since 1950, largely due to the introduction of amphotericin B. Multimodal treatment includes intravenous liposomal or deoxycholate amphotericin B, surgical debridement, and oral posaconazole.^2,6

Although the mortality rate is decreasing, the incidence of mucormycosis is rising globally. In developed countries, these infections are evident in individuals with hematologic malignancies and hematopoietic stem cell transplants. In developing countries, there is a strong association between uncontrolled diabetes mellitus and mucormycosis.^2,5,6

Caitlin Lawlor is a fourth-year medical student at the Lewis Katz School of Medicine at Temple University, Philadelphia. Kiran Motaparthi, MD, is associate professor, residency program director, and director of dermatopathology in the Department of Dermatology at the University of Florida College of Medicine.

References

1.  Stone N, Gupta N, Schwarts I. Mucormycosis: time to address this deadly fungal infection. Lancet Microbe. 2021;2(8):e343-e344. doi:10.1016/S2666-5247(21)00148-8

2.  Castrejón-Pérez AD, Welsh EC, Miranda I, Ocampo-Candiani J, Welsh O. Cutaneous mucormycosis. An Bras Dermatol. 2017;92(3):304-311. doi:10.1590/abd1806-4841.20176614

3. Pak J, Tucci VT, Vincent AL, Sandin RL, Greene JN. Mucormycosis in immunochallenged patients. J Emerg Trauma Shock. 2008;1(2):106-113. doi:10.4103/0974-2700.42203

4. Boelaert JR, Van Cutsem J, de Locht M, Schneider YJ, Crichton RR. Deferoxamine augments growth and pathogenicity of Rhizopus, while hydroxypyridinone chelators have no effect. Kidney Int. 1994;45(3):667-671. doi:10.1038/ki.1994.89

5.  Chakrabarti A, Das A, Mandal J, et al. The rising trend of invasive zygomycosis in patients with uncontrolled diabetes mellitus. Med Mycol. 2006;44(4):335-342. doi:10.1080/13693780500464930

6. Sittig KR, Laageide LG, Akhtar Z, Wall GC, Kumar SC. Cutaneous mucormycosis in a chronic lymphocytic leukemia patient on ibrutinib. IDCases. 2021;24:e01120. doi:10.1016/j.idcr.2021.e01120

7. Hartley M. Tularaemia. DermNet, 2009. Accessed September 12, 2023. https://dermnetnz.org/topics/tularaemia

8. Shah M, Crane JS. Ecthyma gangrenosum. StatPearls.StatPearls [Internet]. Updated June 28, 2023. Accessed September 12, 2023.

9. Simonsen KA, Chatterjee K. Anthrax. StatPearls, StatPearls [Internet], Updated July 25 2023. Accessed September 12, 2023.