Tinea corporis (ringworm)

Clinical presentation

• Typical elementary lesion : erythematous + scaly + circular plaque(s) + with active border (periphery erythematous + vesicular + scaly + more active and more inflammatory than the center) + and healing center (less erythematous + less scaly + paling) → characteristic «target» or «medallion» appearance + pruritus often present + progressive centrifugal extension
• Locations : trunk + limbs + face (tinea faciei) + neck + intertriginous areas + tinea gladiatorum: shoulders + neck + trunk in wrestlers
• Tinea incognito: atypical lesion after application of topical corticoids → pruritus absent or reduced + ill-defined borders + more extensive lesions + sometimes pseudo-nodular or follicular → frequent diagnostic error + anamnesis of recent use of essential dermocorticoids
• Tinea imbricata (Trichophyton concentricum) : tropical form (Pacific + Southeast Asia + South America) → concentric overlapping plaques characteristic + chronic + recurrent + difficult to treat
• Severe inflammatory forms (body kerion): nodules + pustules + follicular abscesses + intense inflammatory reaction → often linked to T. violaceum or zoophilic species + compulsory oral treatment

Diagnosis

• Clinical diagnosis (majority of cases) : sufficiently typical presentation + anamnesis (animal contact + contact sports + travel to tropical areas + use of corticosteroids) + no further tests necessary in typical forms
• Direct examination with KOH (microscope): scraping of active edge of lesion (most productive area) → KOH preparation 10-20 % → visualization of compartmentalized mycelial filaments (hyphae) + characteristics of dermatophytes → sensitivity 70-85 % + results within 30 minutes
• Mycological cultivation (Sabouraud) : species identification + antifungal treatment → 2-4 weeks delay + useful if recurrence + atypical form + suspected resistance + or assessment of associated tinea capitis
• Wood lamp : greenish fluorescence only for Microsporum canis and M. audouinii → negative for T. rubrum (most frequent) → do not eliminate a tinea on the basis of a negative Wood's lamp
• Skin biopsy + PAS staining : rarely necessary + useful if diagnostic doubt with psoriasis + eczema + granuloma annulare + contact dermatitis

Main differential diagnosis

• Plaque psoriasis: chronic erythematosquamous plaques + thick silvery scales + symmetrical localization (elbows + knees + scalp) + absence of active border + KOH negative + personal or family history of psoriasis
• Eczema / atopic dermatitis : pruritic erythematosquamous patches + but bilateral and symmetrical + flexion creases (elbows + knees + nape) + less circular appearance + atopy + high IgE + KOH negative
• Granuloma annulare : ring lesion without scales + no pruritus in general + center not healing + intradermal lesions + KOH negative + biopsy required
• Pityriasis rosé de Gibert: begins with a herald medallion + then secondary «Christmas tree» eruption + internal scaly collar + spontaneous resolution + KOH negative
• Tinea versicolor (pityriasis versicolor) : hypopigmented or hyperpigmented non-annular macules + no active border + KOH: short filaments + «spaghetti-ball» spores (Malassezia) + locations: trunk + shoulders

Treatment

• Topical antifungals (first-line treatment - localized forms) : terbinafine cream 1 % (Lamisil®) 1-2 applications/d × 1-2 weeks → shortest treatment + very effective + or clotrimazole 1 % (Canesten®) 2 applications/d × 2-4 weeks + or miconazole + econazole + ketoconazole + apply to the lesion + 2 cm beyond the edge + continue 1-2 weeks after clinical disappearance to avoid recurrences.
• Oral terbinafine (extensive + multiple + refractory + or immunocompromised forms) : 250 mg/d × 2-4 weeks → very effective + well tolerated + monitor transaminases if treatment is prolonged
• Itraconazole oral (alternative) : 100-200 mg/d × 2-4 weeks + or pulsed regimen + numerous drug interactions (CYP3A4)
• Oral fluconazole (alternative) : 150-200 mg/week × 4-6 weeks + or 50 mg/d × 2-4 weeks
• DO NOT use topical corticoids alone: worsens fungal infection + leads to tinea incognito + extends lesions despite apparent improvement in symptoms
• Preventive measures : avoid sharing towels + clothing + sports equipment + treat symptomatic contacts + treat pets if M. canis (consult your veterinarian) + dry skin thoroughly after showering, especially in folds + change clothes after perspiring profusely

Consult at Clinique Omicron

Clinique Omicron's specialized physicians and nurse practitioners (SPNs) diagnose tinea corporis on clinical examination (ring lesion with active border + KOH if in doubt), prescribe topical (terbinafine cream) or oral antifungal treatment depending on the extent of the lesions, recognize tinea incognito in patients who have applied corticoids, screen for associated tinea capitis in children, advise on preventive measures and decontamination of surroundings and pets. Consultations are available at several points of service in Quebec, as well as via telemedicine. To book an appointment, visit cliniqueomicron.ca.

The contents of this page are provided for information purposes only and do not replace the advice of a physician or dermatologist. Never apply topical corticosteroids alone to a ring lesion in the skin without first ruling out dermatophytosis - this may lead to tinea incognito with silent extension of the infection. Continue antifungal treatment 1 to 2 weeks after clinical disappearance to avoid recurrence.