Tinea Corporis

Etiology

The ability of dermatophytes to attach to the keratinized tissue of the skin forms the basis for dermatophytoses, also termed superficial fungal skin infections.[4] The dermatophytes responsible for tinea corporis belong to the genera Trichophyton, Epidermophyton, and Microsporum. Over the past 70 years, Trichophyton rubrum has been the most common species to cause dermatophyte infections. T rubrum accounts for 80% to 90% of the pathogenic strains.[5] Other common isolates include T mentagrophytes and Microsporum audouinii. Direct skin contact with soil, animals, or other humans typically leads to infection.

In some cases, the most common etiologic species depends on the mode of transmission. Tinea corporis caused by T tonsurans often results from direct contact with a patient with tinea capitis. In the United States and the United Kingdom, T tonsurans is the most common causative agent of tinea capitis.[6][7] This species is also frequently identified in cases of tinea corporis gladiatorum, which typically occurs in athletes with extensive direct skin-to-skin contact, such as wrestlers.[8] Patients with tinea corporis who have close contact with cats or dogs are commonly infected with M canis.

Epidemiology

Tinea corporis is highly prevalent worldwide. Dermatophytes are the most prevalent agents of superficial fungal infections. Excessive heat, high relative humidity, and fitted clothing have correlations to more severe and frequent disease.[9]

Specific populations, such as children, are more predisposed to tinea corporis. [10] Tinea capitis and tinea corporis are the most common dermatophytic infections in prepubertal children.[11] Pediatric patients are also more likely to contract zoophilic infections, which are transmitted through contact with animals, such as cats and dogs. Individuals with compromised immune systems are not only more vulnerable to tinea corporis but also have an increased risk of developing Majocchi granuloma, a form of tinea corporis folliculitis that invades the deep dermal layers, unlike the superficial involvement observed in typical tinea corporis.[12]

Pathophysiology

Susceptibility to fungal infections varies among individuals, with familial and genetic predispositions potentially linked to specific defects in innate and adaptive immunity. A deficiency in defensin β4 may predispose patients to all dermatophytes. Additional risk factors include underlying conditions, such as diabetes mellitus, lymphomas, immunocompromised states, Cushing syndrome, excessive sweating, and advanced age. Current evidence suggests that the control of dermatophytosis primarily depends on a cell-mediated immune response.

Histopathology

Skin scrapings are subjected to microscopic examination after a 10% to 20% potassium hydroxide (KOH) solution is applied. Gentle heating enhances the preparation by dissolving keratin, highlighting the dermatophyte. Under the microscope, septate, branching, and long, narrow hyphae without constrictions can be visualized.

History and Physical

Patients commonly report an itchy, red rash that typically appears on exposed areas of the neck, trunk, or extremities. Physical examination reveals one or more circular or ovoid lesions, often presenting as patches or plaques. These annular lesions show sharp margins with a raised, erythematous, scaly edge, sometimes containing vesicles. The degree of inflammation varies. The lesions expand centrifugally, leaving central clearing with mild residual scaling. This characteristic ring appearance gives rise to the term ringworm.

Evaluation

Tinea corporis is typically diagnosed based on a detailed history and a thorough physical examination. Diagnostic tests can confirm the condition when needed. Microscopic evaluation of skin scrapings with a KOH preparation often reveals septate, branching, long, narrow hyphae. However, false negatives occur in up to 15% of cases when relying solely on KOH preparations.[13]

Fungal culture is another reliable method for confirming the diagnosis. Although fungal cultures can provide definitive identification, they require time for growth. Cultures typically show growth within 5 days, though some species may take up to 4 weeks. A sample is considered to have no growth after at least 4 weeks of lack of fungal colony development. The most commonly used isolation medium is Sabouraud dextrose agar (1% glucose, 4% mycological peptone, water). Identification involves analyzing the morphology, pigmentation, and surface topography of the culture sample.

Performing antifungal susceptibility testing on cultured organisms can help determine the most effective treatment regimen. This step is especially important for cases that are refractory to initial therapy, as it ensures the use of the most appropriate antifungal agent.

Dermoscopy may be used to identify characteristic features of tinea infections.[14] Research has identified 20 dermoscopic features in tinea capitis, 13 in tinea corporis, and 12 in tinea cruris. The most common dermoscopic feature in tinea capitis was corkscrew hairs, observed in 49 out of 110 patients.[15][16]

Treatment / Management

The treatment of dermatophyte infections typically involves topical or oral antifungal agents. The choice between these formulations depends on various factors, such as the severity, location, and extent of the infection; patient comorbidities; and response to previous treatments.

Localized tinea corporis typically improves with topical therapy, applied once or twice daily for 2 to 3 weeks. The endpoint of therapy is the clinical resolution of symptoms. In general, topical nystatin is ineffective for treating tinea corporis.

Recommended topical regimens include one of the following:

• Clotrimazole: 1% cream/ointment/solution applied topically twice daily
• Ketoconazole: 2% cream/shampoo/gel/foam applied once daily
• Miconazole: 2% cream/ointment/solution/lotion/powder applied twice daily
• Naftifine: 1% cream applied once daily or 1% or 2% gel applied twice daily
• Terbinafine: 1% cream/gel/spray solution applied once or twice daily

Oral therapy is necessary in cases involving more widespread infection or failed topical treatment. Oral terbinafine or itraconazole is typically the preferred first-line treatment and is expected to clear the condition in about 2 to 3 weeks.

Recommended oral regimens for adults include one of the following:

• Terbinafine: 250 mg orally once daily for 2 weeks
• Itraconazole: 100 mg once daily for 2 weeks or 200 mg once daily for 1 week; capsules must be taken with food
• Fluconazole: 150 to 200 mg once weekly or 50 to 100 mg/day for up to 4 weeks
• Griseofulvin: 500 to 1000 mg once daily for 2 to 4 weeks  

Recently, trials have shown that tinea corporis caused by terbinafine-resistant T rubrum can be successfully treated with fosravuconazole.[17] In other cases of drug resistance, antifungal susceptibility testing is essential to guide treatment choice and ensure the use of the most effective agent.

Differential Diagnosis

Several diseases in the differential diagnosis can mimic the appearance of tinea corporis, often presenting with annular lesions. Cases that do not respond to antifungal treatment or have a negative KOH microscopic examination should prompt further investigation. Clinicians must also consider more serious conditions, especially in cases with extensive skin involvement or severe disease.

Other common conditions that may present similarly to tinea corporis include nummular eczema, erythema annulare centrifugum, tinea versicolor, cutaneous candidiasis, subacute cutaneous lupus erythematosus, pityriasis rosea, contact dermatitis, atopic dermatitis, seborrheic dermatitis, and psoriasis. Severe diseases that must be ruled out include secondary syphilis, mycosis fungoides, and parapsoriasis.

Prognosis

The prognosis for tinea corporis is generally excellent with appropriate treatment. Most localized cases respond well to topical antifungal agents within 2 to 4 weeks, especially when underlying predisposing factors are effectively addressed. Systemic antifungal therapy is effective in more extensive or refractory cases, with a high success rate when adherence is maintained. Recurrence can occur, particularly in the presence of persistent risk factors, such as immunosuppression, untreated tinea pedis or onychomycosis, and poor hygiene practices. Chronic or recurrent cases may require longer treatment courses or prophylactic measures. Delayed treatment or misdiagnosis can lead to atypical presentations or secondary bacterial infections, potentially complicating the clinical course.

Complications

Complications of dermatophytic infections are rare. One such complication is Majocchi granuloma, a condition where the dermatophyte invades through a follicle and advances deeper into the dermis or subcutaneous tissue. Minor skin trauma, such as shaving, can predispose patients to Majocchi granuloma. Lesions typically involve hair follicles and present as erythematous nodules or papules, which may progress to abscesses. Oral antifungals, such as terbinafine at a dosage of 250 mg once daily for 2 to 4 weeks, are the recommended treatment for this condition.