AKT · Dermatology/Infections & infestations

Cutaneous fungal infection (tinea)

Dermatophytes (Trichophyton, Microsporum) — keratin invasion

Overview

Dermatophyte (ringworm) infection of keratinised tissue: tinea corporis (body), cruris (groin), pedis (athletes foot), capitis (scalp), unguium/onychomycosis (nail). The exam picture is an asymmetrical annular plaque with a raised scaly ACTIVE EDGE and central clearing — KOH/scrape confirms it.

Recognise

Annular ("ring") plaque with a raised scaly leading edge and central clearing; asymmetrical and often single/few
Tinea pedis: itchy scaling/maceration between the toes; tinea cruris: groin (spares the scrotum, unlike candida)
Tinea capitis: scaly patches with hair loss/broken hairs (children) → can form a boggy kerion; tinea incognito if masked by steroids

Red flags

Tinea capitis needs ORAL therapy (topical does not reach the hair shaft); a kerion (boggy inflamed mass) needs prompt treatment to avoid scarring alopecia

Differentials & how to tell them apart

Discoid eczemacoin-shaped but uniformly scaly/crusted, no central clearing, KOH negative

Psoriasissymmetrical silvery extensor plaques, no active advancing edge, KOH negative

Pityriasis roseaherald patch + fir-tree trunk distribution, collarette scale

Granuloma annulareannular but non-scaly, firm dermal papules

Candida intertrigoflexural, beefy-red with satellite pustules, involves the scrotum

Clinical image

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Cutaneous fungal infection (tinea) — clinical imagesDermNet

Investigations

Skin scrapings / nail clippings / hair for microscopy (KOH) and fungal culture — confirm before oral therapy. Wood lamp for some scalp infections.

Management

Localised tinea corporis/pedis/cruris → topical terbinafine or an imidazole

1Confirm with scrapings if uncertain. Localised tinea corporis/cruris/pedis → topical terbinafine (or an imidazole) + general measures (keep dry, treat shoes/feet).Gate: Tinea CAPITIS and onychomycosis need ORAL antifungals (topical cannot penetrate the hair shaft or nail plate) — and confirm by culture before committing to weeks of an oral agent
2Extensive skin disease, nail or scalp involvement → oral terbinafine (griseofulvin or terbinafine for children with tinea capitis); treat the household/fomites for capitis.

Topical terbinafine or an imidazole (clotrimazole) — tinea corporis/cruris/pedis

Oral terbinafine — extensive skin disease, onychomycosis, or tinea capitis (adults)

Oral griseofulvin or terbinafine — tinea capitis (children) — confirm by culture first

Ketoconazole/selenium shampoo — adjunct in scalp disease to reduce spore shedding

Key points

Tinea incognito = the appearance is altered (loss of the scaly edge, more extensive) because a topical steroid was applied to undiagnosed ringworm. Tinea cruris spares the scrotum; candida does not.

Monitor & prognosis

Clinical resolution; LFTs for prolonged oral terbinafine.

Cures with appropriate (and adequately long) therapy; nails take months.

Source: NICE CKS Fungal skin infection; DermNet