Tinea Corporis

Tinea corporis (ringworm) is a superficial dermatophyte infection of the glabrous skin of the trunk and extremities, excluding the scalp, beard, face, palms, soles, and groin. The infection is confined to the stratum corneum.

Polycyclic tinea corporis plaques on the trunk and upper arm (Fitzpatrick's Dermatology)

Etiology

Any dermatophyte can cause tinea corporis. The most common pathogens are:

Organism	Notes
Trichophyton rubrum	Most common overall; responsible for chronic, widespread, and follicular forms
T. mentagrophytes / T. interdigitale	Common; zoophilic strains cause inflammatory lesions
T. indotineae (formerly T. mentagrophytes var. Vill)	Emerging resistant strain, especially from South Asia
Microsporum canis	Common in children; acquired from dogs and cats
T. tonsurans	Cause of tinea corporis gladiatorum in wrestlers
Epidermophyton floccosum	Common in humid climates; no microconidia
T. concentricum	Causes tinea imbricata; restricted to the Far East, South Pacific, Central/South America

Dermatology 5e, p. 1604; Fitzpatrick's Dermatology, p. 2974

Epidemiology & Transmission

Transmitted by direct contact with infected humans (anthropophilic), animals (zoophilic), or soil (geophilic), as well as via fomites or autoinoculation from other body sites (feet are a common reservoir).
Children are more prone to zoophilic infections, especially M. canis from pets.
Risk factors: humid climates, occlusive clothing, skin-to-skin contact, minor skin trauma, immunosuppression.
Tinea corporis gladiatorum: caused by T. tonsurans in wrestlers; head, neck, and arms most affected due to mat contact and skin abrasion.

Clinical Features

Classic presentation:

One or more annular ("ringworm") plaques with a raised, erythematous, scaly border that advances centrifugally
Central clearing (or residual scale) as the active border spreads outward
The border may be vesicular; pruritus is common

Morphologic variants:

Variant	Features
Annular	Classic ring; raised scaly border, central clearing
Polycyclic	Multiple coalescing rings, large confluent plaques
Psoriasiform	Thick scaly plaques mimicking psoriasis; common in immunosuppressed
Tinea imbricata	Concentric scaly rings; minimal vesiculation; caused by T. concentricum
Tinea incognito	Modified by topical steroids - border blurred, scale minimal, widespread hyphae on KOH
Majocchi granuloma	Deep follicular involvement; scaly follicular papules/nodules in annular arrangement; most common on shaved legs of women

Fitzpatrick's Dermatology, p. 2973; Andrews' Diseases of the Skin, p. 347

Diagnosis

1. KOH preparation (potassium hydroxide)

Scrape from the active advancing border (not the center)
Branching, septate hyphae confirm fungal infection
Pitfall: "mosaic false hyphae" from cell wall junctions of normal keratinocytes is the most common artifact mimicking positive KOH
Cotton/synthetic fibers from clothing can also mimic hyphae

2. Fungal culture

Growth visible in 1-2 weeks; identifiable to genus level by gross and microscopic morphology

3. Skin biopsy

Periodic acid-Schiff (PAS) or Grocott methenamine silver (GMS) stain
Useful in chronic refractory cases (tinea incognita)
Hyphae found in the stratum corneum

4. Wood's lamp

M. canis and select Microsporum spp. fluoresce green; Trichophyton spp. do not

Differential Diagnosis

Category	Conditions
Most likely	Erythema annulare centrifugum, nummular eczema, psoriasis, tinea versicolor, subacute cutaneous lupus erythematosus, cutaneous candidiasis
Consider	Contact dermatitis, atopic dermatitis, pityriasis rosea, seborrheic dermatitis
Rule out	Mycosis fungoides, parapsoriasis, secondary syphilis

Fitzpatrick's Dermatology, p. 2974

Treatment

Topical (first-line for localized disease)

Apply to lesion plus 2 cm beyond the active border. Duration: 2-4 weeks (or 1 week for terbinafine).

Drug Class	Examples	Frequency
Allylamines (fungicidal, preferred)	Terbinafine (Lamisil), naftifine (Naftin), butenafine (Mentax)	Once daily; terbinafine can be 1-week course
Imidazoles	Clotrimazole, miconazole, econazole, ketoconazole, oxiconazole, sulconazole	Once or twice daily x 2-4 weeks
Benzylamine	Butenafine	Once daily
Hydroxypyridone	Ciclopirox olamine (Loprox)	Twice daily
Thiocarbamate	Tolnaftate	Twice daily

Allylamines generally require a shorter treatment course than azoles due to fungicidal vs. fungistatic activity.
Avoid combination steroid-antifungal products (e.g., clotrimazole/betamethasone dipropionate) - these frequently produce widespread tinea and fungal folliculitis.

Oral (for extensive, recurrent, or follicular disease)

Drug	Dose	Duration
Terbinafine	250 mg/day	2-4 weeks
Itraconazole	200 mg/day or 100 mg/day	1 week or 2 weeks
Fluconazole	150-200 mg/week	4-6 weeks
Griseofulvin	500 mg/day (microsize)	4-8 weeks

Oral therapy is indicated for Majocchi granuloma, tinea incognito, immunocompromised patients, and widespread/recalcitrant disease.
Andrews' Diseases of the Skin, p. 347; Fitzpatrick's Dermatology, p. 2974

Important note - T. indotineae

This emerging species has high-level terbinafine resistance (due to SQLE gene mutations). Itraconazole or voriconazole may be required. It has been reported increasingly from the Indian subcontinent and in travelers globally.

Special Situations

Immunocompromised patients: More extensive, atypical presentations (polycyclic, psoriasiform); oral therapy usually required.
Tinea corporis gladiatorum: Oral terbinafine preferred; prophylaxis with topical antifungals during wrestling season.
Majocchi granuloma: Oral antifungal required (topical therapy insufficient due to deep follicular involvement); terbinafine 250 mg/day x 4-8 weeks is standard.
Pregnancy: Topical agents preferred; clotrimazole and miconazole are safest; systemic azoles are teratogenic (Pregnancy Category C/D).

Sources: Dermatology 2-Volume Set 5e, p. 1604-1606 | Fitzpatrick's Dermatology 9e, p. 2973-2974 | Andrews' Diseases of the Skin, p. 347

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