What are the likely diagnoses and recommended management for an itchy rash involving the feet, axillae, and groin?

Itchy Rash on Feet, Armpits, and Groin: Diagnosis and Management

Most Likely Diagnosis

The distribution pattern of itchy rash affecting the feet, axillae, and groin strongly suggests tinea corporis (dermatophyte fungal infection), which characteristically affects warm, moist intertriginous areas. 1, 2

Immediate Diagnostic Approach

• Obtain skin scrapings from the active border of lesions for KOH wet-mount examination as point-of-care testing, as clinical diagnosis alone has low accuracy 2
• Look for characteristic features: scaling, erythema, and well-demarcated borders with central clearing 1, 2
• The interdigital spaces of feet (tinea pedis), groin (tinea cruris), and axillae are classic locations for dermatophyte infections 1, 3, 2
• If KOH is negative but clinical suspicion remains high, send fungal culture or molecular testing 2
• Assess for secondary bacterial infection by examining for crusting, weeping, honey-colored discharge, or pustules 4

First-Line Treatment Strategy

For localized disease affecting these three areas, initiate topical antifungal therapy applied once to twice daily for 2-6 weeks. 2

Topical Antifungal Options (in order of preference):

• Terbinafine cream (allylamine) - most effective with shortest treatment duration 3, 2
• Azole derivatives (ketoconazole, clotrimazole, miconazole) 3, 2
• Ciclopirox olamine 3, 2
• Naftifine or amorolfine 3

Application Protocol:

• Apply to affected areas and extend 2-3 cm beyond visible borders 2
• Continue treatment for 1-2 weeks after clinical resolution to prevent recurrence 2
• For feet: treat interdigital spaces and soles thoroughly 1, 3

When to Escalate to Oral Therapy

Oral antifungal therapy is indicated if the rash is extensive across all three body regions, fails topical treatment after 2-4 weeks, or shows signs of deep tissue involvement. 2

Oral Antifungal Options:

• Terbinafine 250 mg daily for 2-4 weeks (first-line systemic agent) 3, 2
• Itraconazole 200 mg daily for 2-4 weeks 3, 2
• Fluconazole 150-300 mg weekly for 2-4 weeks 3, 2

Combined topical and oral therapy may increase cure rates in extensive disease. 2

Adjunctive Symptomatic Management

• Apply hydrocortisone 1% cream to affected areas for severe pruritus, but limit use to 1-2 weeks maximum 4
• Use emollients and soap substitutes to prevent skin barrier disruption 4
• Short-term sedating antihistamines at bedtime may help with sleep disturbance from itching 4

Management of Secondary Bacterial Infection

If signs of bacterial superinfection are present (crusting, weeping, pustules):

• Obtain bacterial culture 4
• Initiate oral antibiotics (e.g., flucloxacillin or cephalexin) for at least 14 days 4
• Continue antifungal therapy concurrently 4

Critical Pitfalls to Avoid

• Do not use potent or very potent corticosteroids in the groin or axillae, as these intertriginous areas have increased absorption risk and high likelihood of skin atrophy 5, 4
• Avoid treating with corticosteroids alone without antifungals, as this will worsen fungal infection 1
• Do not discontinue treatment when symptoms improve; complete the full course to prevent recurrence 2
• Recognize that tinea pedis can serve as a reservoir for recurrent groin and axillary infections through autoinoculation 1, 6

Prevention and Long-Term Management

• Keep affected areas dry, particularly interdigital spaces of feet 1, 2
• Use antifungal powder in shoes and socks 1
• Avoid sharing towels or clothing with infected individuals 2
• Treat all affected family members simultaneously to prevent reinfection 2
• Address predisposing factors such as diabetes or immunosuppression 1

When to Refer to Dermatology

• Failure to respond to appropriate topical therapy after 4 weeks 2
• Diagnostic uncertainty after negative KOH but persistent symptoms 2
• Recurrent infections despite adequate treatment 2
• Immunocompromised patients with extensive disease 1, 2