CASE #1: Tinea faciei

Tinea faciei is an extremely common form of dermatophytosis or superficial fungal infection. Dermatophytosis is caused by one of three genera: Trichophyton, Epidermophyton, or Microsporum. These fungi can be transmitted by other humans, animals, and the soil. These same organisms can cause similar infections elsewhere on the body (e.g., tinea cruris [jock itch] and tinea pedis [athlete’s foot]).1

Given the chronicity and relative lack of overt inflammation in this case, Trichophyton was the likely causative organism. Cats are a common source of what is generally a more acute and inflammatory type of tinea faciei caused by Microsporum, a condition that tends to be more widespread, contagious, and difficult to treat than its more common dermatophytic counterparts.

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Conjecture about the source of tinea faciei amounts to more than mere speculation since re-exposure can lead to recurrences and even spread to other family members, leading to what can seem like a never-ending cycle. Fungal infections of the feet, scalp, or body can spread to the face, but contagion is only one potential impediment to successful treatment.

A bigger problem is often the diagnosis itself. There is a widely held—but mistaken—assumption that a round and scaly rash invariably represents “ringworm.” Most OTC antifungal creams are ineffective, often leading the patient or provider to abandon the presumptive diagnosis and try other medications, including steroid preparations that make things worse and more difficult to treat while casting doubt on the entire diagnostic process.

A KOH preparation demonstrating fungal elements will allow the clinician to proceed confidently with appropriate treatment. A negative KOH should trigger the consideration of other potential diagnoses. In cases of steroid-exacerbated superficial fungal infection, a KOH prep is likely to reveal fungal elements (hyphae) since steroid-induced localized immunosuppression encourages overgrowth of these organisms.

To perform a KOH prep, use a #10 blade to forcefully scrape the periphery of the eruption while holding a glass slide underneath to catch the scrapings. Collect the scrapings into a smaller area so that they fit easily under a coverslip that is then laid on top. The 10% KOH solution is dripped at the edge of the coverslip and will quickly diffuse inward to fill the space between the coverslip and slide.

Next, heat the slide from underneath with a small butane lighter for a second or two, taking care to avoid boiling the fluid. This will eliminate the bubbles that inevitably form and will speed up the digestion of the keratinaceous material, both of which would otherwise obscure the hyphae.

Examined under 10 power, the hyphae will be seen as slender filaments of uniform width that extend linearly across multiple cell walls, often branching in such a way as to resemble streaks of lightning. The hyphae, which can be multiple (especially when steroid-exacerbated) or sparse, will refract light when the fine focal control is moved up and down slightly. Ideally, the slide should be examined immediately. If the results are negative, let the slide sit for a few minutes to allow for the KOH to further thin the keratin. This may reveal hyphae that were initially hidden from view.

A KOH prep is often not performed because other diagnostic possibilities (e.g., eczema, contact dermatitis, psoriasis, seborrhea, and discoid lupus) are not being considered. Patients with eczema tend to be atopic; have dry, sensitive skin; and will have had other episodes of eczema in the past. Areas of the face and arms with eczema will not tan as easily as surrounding skin, thus imparting a depigmented look (pityriasis alba). Contact dermatitis is likely short-term, prominently pruritic, and not as scaly as eczema. Psoriasis tends to manifest in the elbows, knees, and scalp. Likewise, seborrhea will nearly always affect the brow, glabella, nasolabial folds, external auditory meati, postauricular sulcus, scalp, and sternal chest. Discoid lupus almost always appears in sun-exposed skin as an atrophic papulosquamous patch, often with enlarged follicular orifices.

A positive KOH obviates the need to consider any of these diagnoses and provides patient and practitioner diagnostic and therapeutic certainty. To acquire the skill and judgment to perform KOH preps, practice on obviously positive cases (e.g., interdigital athlete’s foot or jock itch) to become familiar with what hyphae look like.

Examination of the patient’s face revealed faint, annular papulosquamous patches on the forehead. After a positive KOH test, twice-daily treatment with topical oxiconazole (Oxistat) was instituted. Two weeks later, the rash was completely cleared. The source of the infection turned out to be a friend of the boy who had a similar history of misdiagnosis and failed treatment of a facial rash. Neither boy was atopic (a known predisposing factor for dermatophytosis) or immunosuppressed.

Had the fungal infection been more extensive and inflammatory, oral treatment with terbinafine (Lamisil, Terbinex) 250 mg/day for one month would have been combined with the topical treatment.