Resistant T rubrum
“The biggest difference with T rubrum resistance is you may not see that widespread infection that we see with T indotineae,” said Caplan. T rubrum is probably the most common dermatophyte that dermatologists see, added Elewski, who encounters a resistant case at least monthly. One such patient, featured in a January 2021 British Journal of Dermatology research letter, cleared on itraconazole and ciclopirox cream but subsequently returned with itraconazole-resistant T rubrum because he had been doctor-shopping for the drug intermittently for years, she said. He cleared on posaconazole 300 mg daily, then was lost to follow-up.
TMVII
A 2023 Emerging Infectious Diseases report highlighted the potential for this dermatophyte to spread among men who have sex with men (MSM), presenting as an itchy, scaly rash affecting the pubic, genital, and buttocks skin. “People don’t generally think of a fungal infection as something that could behave like a sexually transmitted infection (STI),” said Gold.
Caplan and coauthors recently reported the first confirmed US TMVII case in JAMA Dermatology. Many experts suspect that unreported US cases existed previously, he said. “When it circulates in Europe and there’s so much travel, it’s probably here too.”
The fact that T indotineae was formerly called TMVIII has created confusion, added Caplan. “I’ve had patients say, ‘I’m worried I have that resistant ringworm that’s spreading among MSM.’ Whenever we talk about STIs and introduce the word ‘resistant,’ that comes with the potential for stigma, anxiety, and concern.” Fortunately, he said, TMVII has shown no resistance to first-line antifungals.
NYU Langone
Dr. Avrom S. Caplan
Why the Rise
Gold said, “We don’t know for sure why we’re seeing these different drug-resistant species popping up.” One possibility, he said, is the common misuse and overuse of topical antifungals — especially those available overseas in combination with high-potency steroids, such as clobetasol. Consumers use these products for a few weeks until symptoms resolve, then reapply them off and on over years, fueling resistance, said Gold.
“We are worried that with warming temperatures, there’s potential to see expansion of the geographic range of epidemic fungi,” he added. “That could be part of what has fueled recent increases in resistant dermatophytes. But it’s hard to prove.”
Climate change may be behind the emergence of Candida auris, according to a 2022 article in The Lancet Regional Health – Americas. This potentially fatal multidrug-resistant infection spreads easily among sick patients in healthcare facilities, according to a CDC information page on C auris.
Confirming Dermatophyte Infection
“A biopsy will only confirm the presence of fungus,” said Elewski. “Here you will need a lab that knows how to do a fungal culture.” Most state laboratories can do this, she said, as can some hospitals and special labs such as CMM in Cleveland.
It takes a Clinical Laboratory Improvement Amendments–certified lab to perform KOH prep in-house, added Caplan, plus up-to-date gear and knowledge of where and how to scrape and what to look for microscopically. Moreover, identifying T indotineae requires molecular testing available at only a handful of laboratories — listed on the AAD Emerging Dermatophytes webpage — nationwide.
Nevertheless, said Caplan, nailing down a diagnosis can guide treatment, often supplanting empirically prescribed antifungal steroid creams. “Those are probably not going to help. And people may be using those on areas of the body they shouldn’t. Both the clinical clues and the steps to make the diagnosis need to come together. But that’s often easier said than done, especially in a busy practice.”
Identifying resistance requires antifungal sensitivity testing, he added, which few labs perform. “Practically speaking,” said Elewski, “if the patient failed terbinafine, I would try itraconazole. You don’t necessarily need proof” of resistance. But if a patient does not respond to itraconazole and terbinafine clinically, she said that she might consider fungal susceptibility testing.