Newborn with persistent rash on foot despite treatment

Key Points

THE CASE

The anxious first-time parents of a 10-day-old girl bring the baby to your office for urgent evaluation of a rash on the bottom of her right foot that has persisted despite treatment with topical antibiotics and antifungals. The rash was first noticed when the child was 3 days old. Pregnancy, delivery, and immediate postnatal period were normal.

DIAGNOSIS: Tinea pedis

Tinea corporis presents as 1 or more asymmetrically distributed, annular, sharply circumscribed plaques with an advancing, raised, scaling border and central clearing.^4,5 When multiple lesions are present, they may coalesce to form serpiginous plaques.⁴ The use of topical steroids can suppress inflammation and itching while the infection persists.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis includes a variety of other annular dermatoses, including the herald patch of pityriasis rosea, nummular eczema, psoriasis, contact dermatitis, seborrheic dermatitis, tinea versicolor, vitiligo, erythema migrans (Lyme disease), granuloma annulare, fixed drug eruption, and lupus erythematosus.^2,4

DIAGNOSIS

Tinea corporis can often be diagnosed based on the clinical presentation alone. Potassium hydroxide (KOH) wet-mount examination of skin scrapings shows hyphae and confirms infection.^4,5 Fungal culture can be useful if the need for long-term oral therapy is anticipated, the infection seems resistant to standard therapy, or the diagnosis is unclear.⁵ Wood's lamp examination is usually not helpful because most causative organisms do not fluoresce.⁴

ETIOLOGY

Tinea corporis is most commonly caused by the Trichophyton species.⁵ In children with infection caused by T rubrum, T mentagrophytes, or Epidermophyton floccosum, parents with tinea infection (especially tinea pedis or onychomycosis) are commonly the source of infection.⁴