Pediatric Annular Plaque: Tinea vs Nummular Eczema vs Granuloma Annulare
A 4-year-old girl has a 3-week history of a 3 cm annular, scaly plaque on the left cheek with central clearing and a slightly raised erythematous border. She has a pet rabbit at home. No fever, no lymphadenopathy. She was started on a low-potency topical corticosteroid by a telehealth clinician 10 days ago; the plaque has since become larger and more inflamed with a new pustular border. The mother is worried about scarring. KOH prep from the active border shows no fungal elements on the first attempt.
1. How do you interpret the negative KOH and the worsening after topical steroid? What diagnoses remain in play, and what is the significance of the rabbit?
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A single negative KOH does not exclude tinea - sensitivity depends on technique, site, and the amount of scale sampled. The history of worsening with a topical corticosteroid (tinea incognito) is a strong clinical clue: steroids blunt the inflammatory border and can produce a more atypical, pustular, expanding plaque.
Differential remains:
- Tinea faciei (dermatophyte; consider zoophilic species, e.g., Trichophyton mentagrophytes from a rabbit, which tends to be more inflammatory).
- Nummular/discoid eczema - but the central clearing and annular border argue against.
- Granuloma annulare - annular but typically non-scaly, no pustules, and does not usually worsen dramatically with a short steroid course.
- Pityriasis rosea, seborrheic dermatitis, impetiginized plaque.
The rabbit is a meaningful exposure: zoophilic dermatophytes are common in rabbits and can cause inflammatory tinea in children. Ask about handling, cage cleaning, and any lesions on the animal.
Management: stop the steroid, repeat sampling properly (scrape the active scaly border, not the center), and send fungal culture - culture identifies the species, which matters for zoophilic infection and for household management.
2. The repeat culture grows a dermatophyte. Outline treatment and the specific counseling points for a 4-year-old with facial tinea and a household pet.
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Treatment:
- Topical antifungal (e.g., terbinafine or clotrimazole) for limited facial tinea is reasonable, but given the inflammatory/pustular course and possible zoophilic species, oral therapy is often preferred - griseofulvin or terbinafine, dosed by weight, for several weeks. Zoophilic tinea frequently needs systemic treatment and can be more resistant to topical alone.
- Stop the topical corticosteroid - continuing it will perpetuate tinea incognito.
- Treat the source: the rabbit should be examined by a veterinarian and treated; environmental decontamination (cage, bedding) reduces reinfection. This is the counseling point most often missed.
- Household screening: check family members and other pets for lesions; zoophilic tinea spreads readily.
Counseling:
- Facial skin is thin - avoid potent steroids even after treatment to prevent atrophy.
- Complete the full antifungal course even after the plaque looks better, to prevent relapse.
- Warn that zoophilic tinea can be more inflamed and may leave temporary post-inflammatory change, but scarring is uncommon with appropriate treatment.
- Hand hygiene after pet contact; do not let the child sleep with the rabbit during treatment.
3. The mother asks whether the earlier steroid caused permanent damage and whether the plaque will scar. How do you answer, and what follow-up do you arrange?
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Reassurance with honesty:
- A short course of a low-potency topical steroid on the face is unlikely to cause permanent atrophy or scarring; the main harm was masking and worsening the infection (tinea incognito), which is reversible with appropriate antifungal therapy.
- Scarring is uncommon in uncomplicated tinea faciei; post-inflammatory erythema or hyperpigmentation can persist for weeks to months and fades. Deep inflammatory zoophilic infection can occasionally leave slight textural change, so monitor.
Follow-up:
- Recheck in 2–4 weeks to confirm resolution and assess for post-inflammatory change.
- Confirm the pet has been evaluated/treated; if not, relapse is likely.
- If the plaque fails to improve on appropriate therapy, reconsider diagnosis (biopsy, bacterial superinfection, or non-fungal annular dermatosis).
- Document the adverse response to topical steroid so future clinicians avoid repeating it.