What is the diagnosis and treatment for a dry scaly lesion on the right ankle?

Diagnosis and Treatment of Dry Scaly Lesion on Right Ankle

The most likely diagnosis is tinea pedis (athlete's foot), and first-line treatment is topical terbinafine 1% cream applied twice daily for 2 weeks for lesions on the sides of the foot. 1

Differential Diagnosis

The dry, scaly presentation on the ankle is most consistent with:

• Tinea pedis (dermatophytosis simplex): The dry, scaly type commonly affects the sides and bottom of the foot and can extend to the ankle region 2, 3
• Tinea corporis: If the lesion is more isolated and circular, ringworm should be considered, though the ankle location makes tinea pedis more likely 2
• Eczematous dermatitis: Less likely given the isolated ankle location without typical flexural involvement

Key diagnostic features to assess:

• Fine scaling with or without erythema 2
• Pruritus (itching) is common 2
• Check between toes and other foot areas for concurrent infection 2, 3
• Look for nail involvement (onychomycosis), which serves as a reservoir for reinfection 3, 4

Recommended Treatment Approach

First-Line Topical Therapy

For dry, scaly lesions on the ankle/sides of foot, apply topical terbinafine 1% cream twice daily (morning and night) for 2 weeks. 1

• Terbinafine is FDA-approved and cures most athlete's foot while relieving itching, burning, cracking, and scaling 1
• Wash affected skin with soap and water and dry completely before applying 1
• Wash hands after each use 1

Alternative topical agents with proven efficacy:

• Ciclopirox olamine 0.77% cream or gel applied twice daily for 4 weeks achieves approximately 60% cure rate at end of treatment and 85% two weeks post-treatment 2
• Topical azoles (clotrimazole 1%, miconazole, others) applied twice daily 2, 5

When to Consider Oral Therapy

Oral terbinafine 250 mg once daily should be considered if:

• Topical therapy fails after 2-4 weeks 2
• Extensive involvement of multiple foot areas 2
• Concurrent nail infection (onychomycosis) is present 2
• Patient preference for shorter treatment duration with once-daily dosing 2

Oral terbinafine 250 mg daily for 1 week has similar efficacy to 4 weeks of topical clotrimazole but with faster clinical resolution 2. For Trichophyton tonsurans infections, terbinafine appears superior to other agents 2.

Alternative oral agents:

• Itraconazole 100 mg once daily for 15 days (87% mycological cure rate) 2
• Fluconazole (dosing varies by indication) 2

Essential Adjunctive Measures

Implement these preventive strategies to avoid recurrence:

• Careful and thorough drying between toes after showers 2
• Daily changes of socks 2
• Wear well-fitting, ventilated shoes and change shoes/socks at least once daily 1
• Periodic cleaning of athletic footwear 2
• Consider foot powder after bathing, which reduced tinea pedis rates from 8.5% to 2.1% in one study 2

Important Clinical Pitfalls

Do not confuse with infected diabetic foot lesions, which require different management:

• If the patient has diabetes, assess for signs of infection (purulent drainage, erythema, warmth, swelling, pain) 2
• Diabetic foot infections require wound cultures, possible imaging, and often systemic antibiotics targeting Staphylococcus aureus 2
• Dry scaly lesions in diabetics without signs of infection can be treated as tinea pedis 2

Recognize that complete eradication may be difficult:

• Nail involvement and sole infection serve as reservoirs for reinfection 3
• Interdigital athlete's foot is mainly seasonal in temperate climates, with hot-weather exacerbations common 3
• The dry, scaly type (dermatophytosis simplex) often alternates with wet, macerated forms 3

Consider potassium hydroxide (KOH) preparation if diagnosis is uncertain, though treatment can be initiated empirically for typical presentations 2, 5.