All that is Round isn’t Ringworm
By Marie Leger, MD PhD
I saw two patients recently who thought they had ringworm. Guess what. They didn’t! I am always happy—I might even say gleeful—when I get to tell people they don’t have ringworm. It makes me weirdly proud of being a dermatologist and the training and experience that come with that, and proud of being able to “see” things that primary care doctors and patients cannot. It also humbles me that the skin can do some really weird things in response to outside stimuli—like fungi, viruses, and even blue cheese.
by: Amaia Domench
Today we will talk about three round rashes that are not ringworm.
But first, ringworm.
1. Tinea corporis aka “ringworm.” This is actually a pretty cool rash—the fungus that causes it varies based on where you live and what kind of animals you happen to fraternize with. For example, in North America, the most common cause is Trichophyton rubrum, which also causes athlete’s foot. If you have a dog, Microsporum canis may be responsible. My brother-in-law got this in Nepal. The organism there was probably T. interdigitale, which is now the most common cause of tinea corporis in Southeast Asia. Tinea has a characteristic scale to it and a raised outside edge. These fungi like the dead outermost cells of the skin—the stratum corneum—and usually only go deeper than that in immunocompromised people or sometimes after trauma—like on the legs after shaving. In this case it’s called Majocchi’s granuloma. This rash is contagious—family members can all give it to each other, and if you have it on one part of your body it can easily spread to other parts. Dermatologists can sometimes get away with treating it with creams, but sometimes pills are needed.
2. Erythema annulare centrifugum (EAC). This is a really weird one. Harmless, not contagious, but pretty dramatic (Google it.). I will often see patients with this who have already tried to treat it with an antifungal to no avail. Sometimes I biopsy this rash, but I don’t when it’s obvious. With EAC, the scale is INSIDE the ring, which can differentiate it from tinea corporis. Usually, these rashes are not so hard to tell apart. No one knows why this rash happens—but we do know it can be associated with a bunch of random things. Including athlete’s foot (even though it is not a fungus itself), tomatoes, blue cheese, and tuberculosis exposure. I was skeptical of the blue cheese association when I read about it as a resident, but I once had a patient who loved blue cheese and ate it several times a week and when he stopped, his EAC went away. Go figure. If you ever get it, your dermatologist will ask you a lot of seemingly unrelated questions and maybe order some bloodwork.
3. Pityriasis Rosea (PR). It is not dangerous—unless you are pregnant, in which case please see a dermatologist right away because it can be associated with a higher miscarriage rate. Your dermatologist will probably order a syphilis test if you get this rash. You heard me right. Syphilis can look like anything, including PR, and we don’t ever want to miss it, since it’s so contagious and so easy to treat. This can be an awkward conversation to have, but I say that I order it in everyone from nuns to elementary school kids (which I do) really fast and no one usually gets upset. I’ve had it be positive two or three times when I wasn’t expecting syphilis.
4. Granuloma Annulare (GA). This one isn’t scaly! Ringworm (and all the other rashes above) are scaly. I’ve seen GA in kids, young adults, and older people—it shows up as a round, elevated ring. Usually it’s not super itchy, but it can be. There are a bunch of variants of it—when I spent a week in Copenhagen they were treating it with something called photodynamic therapy, but here in the US we use a lot of creams. Last year for some reason I saw a lot of it. COVID? Who knows. I had read some case reports that a new topical medication (called JAK inhibitors, recently FDA approved for eczema) was helpful and found a pharmacy in Florida that compounded it and sent it directly to our patients. It works a lot of the time. Super cool.
All right—that’s it for this week! Not to diss ring worm or anything, but if you think you have it, you may not. We are here for you, regardless.