<prompt> A 60-year old male presented with discoloration, thickening and tunneling of 2 fingernails and one toenail. Which of the following will clinch the diagnosis at the earliestWoods lamp examinationKOH mountSlit smear split skin smearGram stain  <response>: Ans. b. KOH mount Discoloration, thickening and tunneling of two fingernails and one toenail is suggestive of onychomycosis or Tinea unguum. The most impoant test to diagnose this is nail scraping for KOH Tinea unguum Onychomycosis Tinea unguum is the ringworm of nail, usually caused by T rubrum. It causes yellowish discoloration of the nails along with thickening of the nails. The most impoant test to diagnose this is a nail scraping for KOH. Type Affected body pa Causative agent Tinea carporis glabrosa Skin of body or limbsusually non hairy T. verrucosumQ Tinea cruris Dhobijack itch Groin, perineum, thighs, scroturn least and late involvement Trichophyton rubrumQ E. floccosum Tinea capitis Scalp Microsporum canis MCQ T. schoenleini, T. tonsurans Tinea pedis Athelete foot Feet, MC 4th web space T. rubrumQ T. mentagrophyte, E. floccosum Tinea manuum Palms T. rubrumQ Tinea unguum Onychomycosis Nail plate nail beddeg T. rubrumQ T. mentagrophyte, E. floccosum 