DR7.1 | KOH Mount for Superficial Fungal Infection — Summary & Reflection

KEY TAKEAWAYS

The KOH mount is the first-line bedside test to confirm a superficial fungal infection before starting antifungal therapy. Its principle is selective keratin clearing: KOH (10–20%) digests human keratin and debris while the chitinous fungal wall resists, revealing fungal elements against a cleared field. Technique is decisive — scrape the active scaly margin (subungual debris for nails; plucked hairs for scalp), mount in KOH under a coverslip, warm gently without boiling, wait 10–15 minutes, and read at 10× then 40× with reduced light. Interpretation: dermatophytes = long branching septate hyphae; Candida = pseudohyphae + budding yeast; Malassezia furfur = short curved hyphae + round spores ("spaghetti and meatballs"); and the mosaic artefact (refractile, non-branching, cell-border network) is the false positive to exclude. A negative KOH does not exclude infection — repeat or culture. The Wood's lamp gives green fluorescence with Microsporum but NOT Trichophyton (the predominant Indian cause of tinea capitis), and fungal culture guides management of recalcitrant tinea where terbinafine resistance is now common in India.

REFLECT

Think back to a patient you have seen — or imagine the man in the opening scenario — with a chronic, spreading, steroid-modified rash that the eye alone could not confidently diagnose. How would performing a KOH mount at that first visit have changed your management, and what would you have done differently if the KOH were unexpectedly negative despite a convincing clinical picture? Consider how you will build the discipline of scraping the active margin, allowing adequate clearing time, and distinguishing true hyphae from the mosaic artefact into your routine, so that this two-minute test becomes a reflex rather than an afterthought. Honest reflection on your own false negatives is what will make you reliable at the bedside.