Superficial dermatophyte (and Malassezia) infections of skin, hair, and nails with site-specific presentations.
Also known as: tinea, ringworm, dermatophytosis, athlete's foot, jock itch, tinea versicolor, pityriasis versicolor
Overview
Superficial fungal infections of keratinized tissue. Dermatophyte tineas (Trichophyton, Microsporum, Epidermophyton) cause classic ringworm of body (corporis), scalp (capitis), feet (pedis), groin (cruris), hands (manuum), and nails (unguium/onychomycosis). Tinea versicolor (pityriasis versicolor) is caused by Malassezia furfur — a yeast, not a true dermatophyte.
Epidemiology
Tinea pedis is the most common dermatophytosis worldwide (~10% point prevalence). Tinea capitis predominantly affects prepubertal children, especially Black children in the US (Trichophyton tonsurans). Tinea versicolor is common in adolescents and young adults in humid climates.
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Question 1DermatologyEasy
A 7-year-old child has a circular scaly erythematous lesion with central clearing on his arm. KOH preparation of skin scraping shows septate hyphae. Which of the following is the most likely diagnosis?
AAtopic dermatitis
BPityriasis rosea
CTinea corporis
DNummular eczema
Reveal answer & full explanation
Correct answer: C — Tinea corporis
AAtopic dermatitis
BPityriasis rosea
CTinea corporis✓
DNummular eczema
Why Tinea corporis is correct
Tinea corporis (ringworm): dermatophyte infection caused by Trichophyton, Microsporum, or Epidermophyton species
Presents as an annular plaque with central clearing, raised scaly border, and occasionally pustules
KOH preparation showing septate, branching hyphae is the key diagnostic finding
Treatment: topical antifungal for 2–4 weeks (clotrimazole, terbinafine, ketoconazole)
Why the others are wrong
Atopic dermatitis — pruritic flexural eczema; does not present as a ring-shaped lesion with central clearing; KOH negative
Pityriasis rosea — begins with a herald patch, then a Christmas-tree distribution on the trunk; KOH negative
Nummular eczema — coin-shaped pruritic plaques but without central clearing; KOH negative
Additional high-yield points
Tinea capitis (children): scaly scalp, hair loss, kerion (boggy inflammatory mass); requires systemic treatment with griseofulvin or terbinafine for 6–8 weeks
Tinea pedis: athlete's foot
Tinea cruris: jock itch
Tinea unguium (onychomycosis): nail infection requiring systemic terbinafine for 6–12 weeks
Question 2DermatologyMedium
A 36-year-old woman has annular plaques with central clearing on the thigh. KOH preparation shows branching septate hyphae. Which of the following is the most appropriate treatment?
ATopical permethrin cream
BTopical terbinafine cream
COral acyclovir capsules
DTopical mupirocin ointment
Reveal answer & full explanation
Correct answer: B — Topical terbinafine cream
ATopical permethrin cream
BTopical terbinafine cream✓
COral acyclovir capsules
DTopical mupirocin ointment
Why Topical terbinafine cream is correct
Annular plaques with central clearing plus septate branching hyphae on KOH confirm tinea corporis.
Terbinafine is fungicidal against dermatophytes and is first-line for localized disease.
A topical agent suffices when only limited, non-hair-bearing skin is involved.
Why the others are wrong
Topical mupirocin ointment — Mupirocin targets gram-positive bacteria for impetigo and has no antifungal action; a rash-treatment trap.
Oral acyclovir capsules — Acyclovir treats herpesvirus, which causes grouped vesicles, not KOH-positive plaques.
Topical permethrin cream — Permethrin kills scabies mites and lice, not dermatophytes.
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Family member with tinea capitis (shared combs, hats)
Pathophysiology
Dermatophytes secrete keratinases that allow invasion of stratum corneum, hair, and nail. Inflammation results from host immune response; minimal inflammation in immunosuppressed → 'tinea incognito' under steroids. Malassezia is a lipophilic yeast colonizing sebaceous skin; conversion from yeast to mycelial form produces clinical pityriasis versicolor; azelaic acid produced by the organism inhibits melanocytes (hypopigmentation).
Clinical presentation
Symptoms
Pruritus (mild to moderate)
Scalp scaling, hair loss (capitis)
Burning, fissuring between toes (pedis)
Cosmetic concerns (versicolor)
Signs / physical exam
Tinea corporis: annular erythematous plaque with raised scaly active border and central clearing; satellite lesions if extensive
Tinea capitis: scaly patches with broken hairs ('black dot' pattern from endothrix T. tonsurans); kerion = boggy inflammatory mass with pustules and lymphadenopathy; favus = yellow scutula crusts
Onychomycosis: yellow/white nail discoloration, subungual hyperkeratosis, onycholysis, dystrophy (distal subungual most common)
Tinea versicolor: hypo- or hyperpigmented finely scaling macules and patches on upper trunk, neck, shoulders; 'fawn-colored' or pink in untanned skin
Classic findings
Active raised scaly border with central clearing (corporis); KOH 'spaghetti and meatballs' (versicolor); Wood's lamp yellow-green fluorescence (Microsporum tinea capitis).
Differential diagnosis
Nummular eczema — Coin-shaped, no central clearing, KOH negative
Psoriasis — Silvery scale, extensor surfaces, nail pitting
Seborrheic dermatitis — Greasy scale in seborrheic distribution
Erythrasma (groin/folds) — Coral-red Wood's lamp fluorescence (Corynebacterium minutissimum); thin brown patches; treat with erythromycin/clindamycin
Granuloma annulare — Smooth annular skin-colored to violaceous papules without scale; KOH negative
Alopecia areata (vs tinea capitis) — Smooth bald patches without scale, exclamation point hairs, no broken hairs at scalp; KOH/culture negative
Vitiligo (vs tinea versicolor) — Complete depigmentation, no scale, Wood's lamp bright milky white fluorescence
Diagnostic workup
Diagnostic criteria
KOH and/or culture positivity in characteristic clinical setting.
Labs
KOH preparation of scale or hair: branching septate hyphae (dermatophyte) or short hyphae + spores ('spaghetti and meatballs') for versicolor
Fungal culture (Sabouraud or DTM agar) — confirms species, especially for capitis and onychomycosis before systemic therapy
Wood's lamp: blue-green fluorescence with Microsporum tinea capitis (T. tonsurans is non-fluorescent); pale yellow with versicolor; coral-red with erythrasma
PAS-stained nail clipping or PCR for onychomycosis diagnosis
Baseline LFTs before oral terbinafine or itraconazole
Imaging
Not indicated
Diagnostic algorithm
Variant
Site / Lesion
Preferred Therapy
Corporis (ringworm)
Annular plaque, raised scaly border, central clearing
Topical azole or terbinafine 2-4 wks
Capitis
Scaly scalp, broken hairs, ± kerion
Oral terbinafine or griseofulvin × 4-8 wks + antifungal shampoo
Pedis
Interdigital maceration; moccasin hyperkeratosis
Topical terbinafine; oral if moccasin/extensive
Cruris
Inguinal scaly plaques sparing scrotum
Topical azole or terbinafine
Onychomycosis
Yellow nail, subungual debris, onycholysis
Oral terbinafine 6 wks (fingers) / 12 wks (toes)
Versicolor
Hypo/hyperpigmented finely scaling macules on trunk
Selenium sulfide or ketoconazole shampoo; oral itraconazole if extensive
Tinea capitis (REQUIRES SYSTEMIC): oral griseofulvin (microsize) 20-25 mg/kg/day × 6-8 weeks (preferred for Microsporum) OR oral terbinafine 3-6 mg/kg/day × 4-6 weeks (preferred for Trichophyton tonsurans, more common in US); adjunctive selenium sulfide or ketoconazole shampoo 2-3x/wk reduces shedding and transmission
Onychomycosis: oral terbinafine 250 mg daily × 6 weeks (fingernails) or 12 weeks (toenails) — most effective; alternatives: itraconazole pulse, fluconazole weekly; topical efinaconazole or tavaborole if oral contraindicated
Tinea versicolor: topical selenium sulfide 2.5% lotion, ketoconazole 2% shampoo, or clotrimazole — lather, leave 10 min, rinse — daily × 1-2 weeks; or oral itraconazole 200 mg/day × 5-7 days for widespread/refractory (avoid oral fluconazole single-dose regimens that were once popular — relapse common)
Kerion (inflammatory tinea capitis)
Oral antifungal (terbinafine or griseofulvin) PLUS short course oral prednisone 0.5-1 mg/kg/day × 5-10 days to reduce scarring alopecia
Antibiotic only if bacterial superinfection — DO NOT drain kerion (sterile inflammation)
Tinea incognito (steroid-modified)
Discontinue topical corticosteroid
Treat with appropriate antifungal — often requires systemic therapy because of extensive subclinical spread
Second-line / adjunct
Avoid systemic ketoconazole due to hepatotoxicity and adrenal suppression risk (FDA boxed warning)
Recheck culture and consider drug resistance (e.g., Trichophyton indotineae — emerging terbinafine-resistant species)
Counsel on hygiene: clean and dry skin folds, antifungal foot powder, change socks, treat shoes with antifungal spray
Complications
Scarring alopecia from untreated kerion
Bacterial superinfection (impetigo, cellulitis), especially with maceration
Onychomycosis: chronic relapsing course, gateway for cellulitis in diabetics
Id reaction (autoeczematization): vesicular dermatitis on hands during active tinea pedis — sterile, immune-mediated
Terbinafine adverse effects: hepatotoxicity, taste disturbance, drug interactions (CYP2D6)
Tinea cruris spares the scrotum; candida intertrigo involves the scrotum with satellite pustules — quick distinguishing feature.
Pruritic annular plaque with central clearing and active border = tinea corporis until proven otherwise — KOH first, treat empirically only if KOH unavailable.
NEVER use topical betamethasone/clotrimazole combination (Lotrisone) — the steroid potency is too high for the skin folds where it is commonly used; causes atrophy and tinea incognito.
Tinea capitis is the only superficial fungal infection that REQUIRES systemic therapy — topicals will not penetrate hair shaft.
Tinea versicolor responds to therapy but pigment changes can take months to fade — counsel patients to avoid attributing relapse to treatment failure.
References
AAD 2014 — Guidelines of Care for Superficial Mycotic Infections of the Skin: Tinea Corporis, Tinea Cruris, Tinea Pedis (Drake et al.; updated standards)
Cochrane 2016 — Systemic Antifungal Therapy for Tinea Capitis in Children (Chen et al., Cochrane Database Syst Rev 2016)
AAFP 2014 — Diagnosis and Management of Tinea Infections (Ely, Rosenfeld, Stone, Am Fam Physician 2014)
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