Does ringworm need to be retreated if the lesion still glows under a Wood's (ultraviolet) lamp after initial treatment?

Wood's Lamp Fluorescence Does Not Guide Retreatment Decisions for Ringworm

Wood's lamp fluorescence is not a reliable indicator for determining whether ringworm requires retreatment, as most common dermatophytes causing tinea corporis do not fluoresce, and treatment decisions should be based on clinical appearance and mycological confirmation rather than Wood's lamp findings. 1

Why Wood's Lamp Has Limited Utility for Ringworm

Most Dermatophytes Don't Fluoresce

• Only certain species like Microsporum canis show green fluorescence under Wood's lamp examination, while most common dermatophytes causing ringworm (tinea corporis) do not fluoresce at all 1
• The British Association of Dermatologists notes that Wood's lamp is primarily useful for identifying M. canis infections and favus, but has limited application for the majority of ringworm cases 1

Clinical and Mycological Assessment Are the Standards

Treatment success should be determined by mycological cure (negative KOH preparation or culture), not clinical appearance alone or Wood's lamp findings. 2

• The British Journal of Dermatology recommends that the definitive endpoint for treatment should be mycological cure, confirmed through repeat microscopy or culture 2
• Follow-up with repeat mycology sampling is recommended until mycological clearance is documented 2

When to Consider Retreatment

Indications for Additional Therapy

Retreatment is indicated when there is incomplete healing by 3 months after completion of the treatment course, development of new skin lesions, or worsening of existing lesions. 3

• Treatment failure should be assessed by physical appearance: relatively little improvement or worsening while on therapy suggests an inadequate response 3
• A common pitfall is stopping treatment too early based only on clinical improvement rather than mycological cure 2

Treatment Duration Guidelines

• According to FDA labeling for griseofulvin, tinea corporis typically requires 2 to 4 weeks of treatment 4
• Medication must be continued until the infecting organism is completely eradicated as indicated by appropriate clinical or laboratory examination 4
• Clinical relapse will occur if medication is not continued until the infecting organism is eradicated 4

Practical Approach to Treatment Monitoring

What to Monitor

• Collect specimens for KOH microscopy using a blunt scalpel to remove skin scale from the active border of lesions 2
• KOH preparation typically shows hyphae and/or arthroconidia if infection persists 2
• Fungal culture on Sabouraud agar with cycloheximide should be incubated for at least 2 weeks 2

Common Pitfalls to Avoid

• Do not rely on Wood's lamp fluorescence to determine treatment success or failure 1
• Do not stop treatment based solely on clinical improvement without mycological confirmation 2
• Do not overlook secondary bacterial infection in inflammatory cases, which may require separate treatment 2

If Treatment Fails

• Treatment failure may require extending treatment duration or switching to an alternative antifungal agent 2
• Consider whether the patient has been compliant with the full treatment course 4
• Reassess the diagnosis with repeat mycological testing to confirm the organism and rule out resistant strains 2