What is the appropriate treatment for small pustules on the plantar surface of the feet that occasionally rupture?

Treatment of Small Pustules on the Bottom of Feet

Based on the clinical presentation of small pustules on the plantar surface that occasionally rupture, the most likely diagnosis is tinea pedis (vesiculopustular form), and you should initiate topical antifungal therapy with either ciclopirox olamine 0.77% cream twice daily for 4 weeks or terbinafine 1% cream once daily for 1 week. 1

Diagnostic Considerations

The key differential diagnoses for pustules on the plantar feet include:

• Tinea pedis (vesiculopustular form): Most common cause, presents with vesiculopustular eruptions that are often itchy, caused primarily by Trichophyton rubrum and T. mentagrophytes 1
• Palmoplantar pustulosis: Chronic condition with sterile pustules, often associated with psoriasis in 20% of cases, but notably does NOT respond to TNF antagonists 2
• Bullous tinea: Can present with blisters/pustules on plantar surfaces 3

First-Line Treatment Approach

For Presumed Tinea Pedis (Most Likely):

Topical antifungal therapy is the primary treatment:

• Ciclopirox olamine 0.77% cream or gel: Apply twice daily to affected areas for 4 weeks

  • Achieves ~60% mycological cure at end of treatment, 85% two weeks post-treatment 1
  • Superior to clotrimazole 1% cream 1

• Terbinafine 1% cream: Apply once daily for 1 week

  • Similar efficacy to 4 weeks of clotrimazole but with faster clinical resolution 1
  • Advantage of shorter treatment duration and once-daily dosing 1

If Topical Treatment Fails:

Oral terbinafine 250 mg once daily for 1-2 weeks 1

• Similar mycological efficacy to itraconazole 100 mg but may have slightly lower relapse rates
• Well tolerated; monitor for rare neutropenia or liver dysfunction in patients with pre-existing liver disease

Important Clinical Pitfalls

Do NOT assume palmoplantar pustulosis without proper evaluation:

• If pustules are sterile (no fungal elements on KOH prep) and associated with psoriasis elsewhere, consider palmoplantar pustulosis
• Avoid TNF antagonists for palmoplantar pustulosis - they are ineffective and may paradoxically worsen the condition 2
• For confirmed palmoplantar pustulosis: Consider oral PUVA therapy (first-line PUVA treatment) 4 or combination oral PUVA with oral retinoids (100% clearance in some studies vs. 44% with PUVA alone) 4

Consider fungal culture or KOH preparation if:

• Diagnosis is uncertain
• Treatment failure occurs
• Atypical presentation 3

Prevention Strategies

To prevent recurrence of tinea pedis 1:

• Use foot powder after bathing (reduces rates from 8.5% to 2.1%)
• Careful and thorough drying between toes after showers
• Daily sock changes
• Periodic cleaning of athletic footwear
• Avoid walking barefoot in communal areas

When to Refer

Refer to dermatology if:

• No response to appropriate antifungal therapy after 4-6 weeks
• Pustules are sterile on culture/KOH prep (suggests palmoplantar pustulosis)
• Associated with psoriasis elsewhere on the body
• Severe, debilitating symptoms affecting quality of life 5

Special Considerations for Diabetic Patients

If the patient has diabetes 6:

• Provide appropriate treatment for fungal infections to help prevent foot ulceration (Strong recommendation)
• Educate patient to examine feet daily
• Ensure proper footwear that accommodates foot shape
• Rapid contact with healthcare professional for any pre-ulcerative lesions