Dispelling Myths In Podiatric Dermatology: Part 2

Patients and clinicians alike are subjected to a barrage of information daily, and sometimes, this information yields misconceptions about common conditions. Despite the best of intentions, this misunderstanding can lead to an incorrect diagnosis or improper treatment. In addition, this can hinder one’s efforts to accurately and effectively educate patients.

In dispelling these 2 podiatric dermatology myths, I challenge practitioners to be skeptical of solely handed-down information and embrace an approach based on evidence, a strong history and physical examination, and appropriate testing.

Myth #1: One Topical Combination Drug Cures All

We have all been there: a patient with a red itchy rash is sitting in front of you and you think to yourself, “What is this and how do I treat this?” You go back to your residency training and remember seeing your attendings prescribe a steroid-antifungal therapy. In particular, Lotrisone (clotrimazole and betamethasone cream). You think this is a slam dunk because the topical “covers both worlds”: if it is fungal, it will cover any fungus there, and if it is inflammatory, the steroid will cover that.

Logical? Yes. Incorrect? Absolutely.

What is the problem with this topical duo and the treatment of rashes? Tinea or superficial dermatophyte infections are incredibly common on all parts of the skin and can be very challenging to diagnose due to their similar appearance at times to other skin diseases. They can appear with vesicles, erythema, scale, pruritus, and sharply dermarcated borders.¹ When a rash is a superficial dermatophyte infection, of which Trichophyton rubrum is the most common cause, the application of a topical (or systemic) corticosteroid creates an altered response within the skin’s immune system. The topical steroid portion suppresses the local immune response, which allows fungus to bloom or manifest abundantly.² This results in a fungal overgrowth called “tinea incognito.”

Now, we often diagnose tinea infections clinically. However, tinea can mimic other skin conditions such as psoriasis or eczema. I see the misdiagnosis of skin conditions almost weekly in my clinic, where well-intentioned practitioners consider every lower extremity skin rash as fungal based without consideration of the many other issues that may present in the same location.

I advocate for one to take the so-called blinders off and delve more deeply into the diagnosis. I advocate to stop prescribing the antifungal/steroid cream completely, and instead, take the time to ask a few more questions such as: “Do you or any of your family members have a history of psoriasis, eczema, or skin cancer?” or “Have you tried any over the counter products to manage this and what was the result?” These simple questions can lead you to the conclusion that you may or may not be dealing with a tinea infection and may encourage you to take a small punch biopsy (for pathology), skin scraping (for fungus), or refer out to another practitioner if you are not comfortable. All of these are acceptable options since the application of a steroid/antifungal combination can do a lot more harm ultimately.

In India, where there is emergence of terbinafine resistance and an epidemic of dermatophyte infections, researchers recently stated: “Indiscriminate use of fixed-drug combination (FDC) of corticosteroids with one or more antifungal and antibacterial agents has been cited as a major reason for the emergence of chronic, atypical, recurrent, recalcitrant, and treatment-resistant cases of superficial dermatophytosis in epidemic proportion.”³

If you do see tinea incognito because of an application of a steroid based product to a fungal infection, you should discontinue topical steroid use and prescribe topical or oral antifungal therapy or both. I advocate the “keep it simple” principle to avoid this in the future. Dermatophyte infections should be treated with an antifungal, inflammatory based conditions with a topical steroid to start, and bacterial infections with an antibiotic.

Let’s stop the myth that a combination of a steroid and antifungal cream has any place in our prescribing habits.

Myth #2: Erythrasma Is Only Fungus-Based

Interdigital areas are subject to humid sock/shoe conditions, lack of airflow between toes, and generally being a “forgotten” place in the foot. It is logical that the maceration that occurs from skin-on-skin contact will become home to fungus, bacteria, and skin breakdown. Many patients I have seen from urgent care, the emergency department, or other practitioners will present with a weeping, painful, itchy interdigital area with just a topical antifungal in hand. I have also spoken to a lot of practitioners who prescribe an oral antifungal with betadine soaks and wonder why the patient is not improving.

It is a myth that fungus can only cause issues between the toes. When patients present with mild or severe issues interdigitally, I utilize a Wood’s Lamp (readily available on Amazon and inexpensive) and inspect if there is any bacterial superinfection that might be the source of the patient’s perturbation.

Erythrasma is a superficial bacterial infection of the intertriginous areas and on the lower extremities involving the digital interspaces.⁴ Interdigitally, erythrasma presents as a chronic scaly rash that may or may not have maceration or be malodorous. It is mostly associated with Corynebacterium minutissimum, a member of the normal skin flora that can invade the stratum corneum in a warm, moist environment. Corynebacterium produces porphyrin that fluoresces coral-red under the Wood’s lamp. A Wood’s lamp exam can easily be done in a clinical setting but should optimally be performed in a darkened room. Also, Pseudomonas can cause an invasion on the interspaces and will fluoresce green with a Wood’s lamp examination. Differential diagnoses include interdigital tinea pedis, candidal infection, inverse psoriasis, and contact dermatitis. Treatment typically consists of topical or oral erythromycin, clindamycin, or Whitfield’s ointment.⁴

Most of the time, it is easy to apply a Wood’s Lamp to the area and determine if there is any fluorescence. If unsure after that in-office exam, there is a non-invasive polymerase chain reaction (PCR) lab test that will identify if the source of the issue is a dermatophyte, yeast, or bacteria. Once you know which organism you are dealing with, then you may prescribe appropriately. However, I often use hypochlorous acid in these patients to act as a broad-spectrum antimicrobial. It is a fast-drying spray, readily available over the counter, and easy to use for those with mobility issues. Also, erythrasma often presents with frank pruritus dorsally on the foot that manifests as a hyperpigmented plaque or vesicles. Patients will describe the discomfort of this aspect of erythrasma more than the interdigital symptoms. I will prescribe a topical steroid to manage the dorsal pruritus, with strict instructions that the patient does not use the steroid in between the toes or on any ulcerations that might be present plantarly.

Interdigital infections absolutely can be fungus-based, but if you have a patient who relates dorsal itching, interdigital dryness or maceration, and plantar sulcus ulceration, consider a diagnosis of erythrasma instead and treat accordingly.

Final Thoughts

Lower extremity dermatological myths can persist not just among patients, but physicians as well. The next time you encounter these with a patient or resident, consider the above information and work to a clarity of diagnosis and treatment that will resolve the condition in question.

Dr. Vlahovic is a Clinical Professor in the Department of Podiatric Medicine at the Temple University School of Podiatric Medicine in Philadelphia.

Click here to read Part 1 of this article.

References

1.     Nowowiejska J, Baran A, Flisiak I. Tinea incognito-a great physician pitfall. J Fungi (Basel). 2022 Mar 18;8(3):312. doi: 10.3390/jof8030312. PMID: 35330314; PMCID: PMC8951265.
2.     Yu C, Zhou J, Liu J. Tinea incognito due to microsporum gypseum. J Biomed Res. 2010 Jan;24(1):81-3. doi: 10.1016/S1674-8301(10)60014-0. PMID: 23554617; PMCID: PMC3596541.    
3.     Rana P, Ghadlinge M, Roy V. Topical antifungal-corticosteroid fixed-drug combinations: Need for urgent action. Indian J Pharmacol. 2021 Jan-Feb;53(1):82-84. doi: 10.4103/ijp.ijp_930_20. PMID: 33976006; PMCID: PMC8216118.
4.     Vlahovic TC, Schleicher SM. Skin Disease of the Lower Extremities: A Photographic Guide. HMP Communications; 2012.