Diagnosing unusual fungal diseases: Phaeohyphomycosis

Photo: Kate/Adobe Stock

Why are fungal diseases often difficult to identify and how should veterinarians approach these dermatological cases? In her lecture, "Dermatologic Conundrums: Fungal Diseases," presented at the Fetch Coastal conference in Atlantic City, New Jersey, Joya Griffin, DVM, DACVD, lectured on unusual fungal diseases and offered approaches for a diagnosis.

“They're things that when they come into [the] clinic, they look very atypical... It's not something that you would treat on a day-to-day basis. It's going to be a little bit different, a little bit unusual, maybe severe. Sometimes these have been going on for a long time,” Griffin said.¹

With challenging dermatologic cases, returning to the basics is essential. Considering factors like the patient’s travel history, indoor/outdoor status, medications, and prior treatments or flea control measures is crucial. This information is important for excluding possible conditions and formulating a differential diagnosis. In her lecture, Griffin also shared that she likes to begin with cytology.

With climate change, fungal diseases have been on the rise. “If you're from the northeast, you may think that you may not see a lot of fungal disease. However, it's coming with climate change… And some of these [unusual fungal] cases, actually one of the very first cases I did see when I was at Cornell [University] in New York over 10 years ago,” said Griffin.

Phaeohyphomycosis

In her session, Griffin also shared dermatological cases with severe and unusual presentations that were not responding to empirical treatment and required multimodal therapy and experimental treatments. One such case was of Buttercup, a 9-year-old domestic shorthair indoor/outdoor castrated male feline, who presented with a nonhealing wound on the right forepaw. Buttercup had a visibly pigmented dorsal lesion.

Griffin shared that she began with a fine needle aspirate, which showed filamentous pigmented organisms. The diagnosis was confirmed as phaeohyphomycosis, a fungal infection typically seen in canines and caused by inoculation into wounds through bites or wood, and caused by pigmented, dematiaceous fungi.

“Usually these limbs [with phaeohyphomycosis], these lesions, will have kind of a blue, gray, pigmented look to them, and they can resemble abscesses like cysts in the tissue, and so they're often treated as a foreign body perennial, especially in dogs. They’re fairly uncommon in cats…,” Griffin explained.

Diagnosing these cases will typically come from cytology, Griffin noted. However, biopsying patients and doing tissue cultures is often necessary.

Talking about Buttercup’s case, Griffin said, “so what's important about this case is that he required long course of systemic therapy to try to keep this disease at bay. And this was really a limb sparing technique, because in other instances, this cat would have had his leg amputated.”

According to Griffin, Buttercup did well for approximately 2 years. “We ended up tapering him to pulse dosing, which is where, instead of giving the antifungal [treatment] every single day, we would do a week on, a week off, to try to keep the disease at bay,” Griffin said. However, the lesions recurred, and Buttercup’s owners eventually decided to have his leg amputated.

Griffin explained that phaeohyphomycosis lesions can usually be seen. “If you have a solitary nodule, or even abscess draining tract type lesions, you can see that pigment in the surface of the skin. So, looking at it clinically, you might be able to find that. If you're able to do an aspirate of it, I'd recommend doing fine needle aspirate and looking at the cytology... And then if things aren't improving with empirical therapy, I would definitely biopsy and consider tissue culture,” she explained.

According to Griffin, treatment for the condition involves excision, or systemic antifungal therapy if attempting a limb-sparing technique.

Reference

Griffin J. Dermatologic Conundrums: Fungal Diseases. Presented at: FetchCoastal; October 14-16, 2024; Atlantic City, NJ.