<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 earliest?Woods lamp examinationKOH mountSlit smear split skin smearGram stain  <response>: Ans. b. KOH mount Ref: Rooks 7e p36.18Discoloration, thickening, and tunneling of two fingernails and one toenail is suggestive of onychomycosis or Tinea unguum. The most important test to diagnose this is naif scraping for KOH.Tinea unguum OnychomycosisTinea 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 important test to diagnose this is a nail scraping for KOH.TypeAffected body partCausative agentTinea carporis glabrosaSkin of body or limbsusually non hairyT. verrucosumQTinea cruris Dhobijack itchGroin, perineum, thighs, scrotum least and late involvementTrichophyton rubrumQE. floccosumTinea capitisScalpMicrosporum canis MCQT. schoenleini, T. tonsuransTinea pedis Athelete footFeet, MC 4th web spaceT. rubrumQT. mentagrophyte, E. floccosumTinea manuumPalmsT. rubrumQTinea unguum OnychomycosisNail plate nail bedQT. rubrumQT. mentagrophyte, E. floccosum 