<prompt> Wood lamp is used to diagnose?PsoriasisTinea versicolorPityriasis rosaeErysipelas  <response>: Ans. b Tinea versicolor. Ref. Harrison, Internal Medicine, 15th ed., 308DIAGNOSTIC TECHNIQUES IN SKIN DISEASES Skin biopsy KOH preparation: To identify hyphae in dermatophytosis, e.g. fragmented hyphae with spores pseudohyphae, yeast in Candida. Tzanck smear. Staining with GiemsaWright stain. To identify herpes infection multinucleated giant cells Diascopy: To assess if lesion blanches with pressure, e.g. haemangioma, granuloma apple jelly app. Woods lightAamp: 360 nm UV light used. Specific finding as following may be diagnostic:- Erythrasma - Wound with pseudomonas - Tinea capitis microspora canisaudouini - Freckles - Hyperpigmentation - Vitiligo - Ash leaf spots- Demonstration of tinea versicolorcoral red colorpale blueyellow fluorescenceaccentuatedfadestotally whitetuberous sclerosis Patch testTINEA VERSICOLOR: Causative agent: Malassezia furfur. Macules of variegated color, growing rapidly. KOH preparation reveals classic Spaghetti meat balls appearance. Topical Rx with selenium sulphide lotion and ketoconazole shampoo.PITYRIASIS ROSEA: Causative agent: HHV 7. Herald patch and Collarette scale lesions Christmas-treepattern of annular patches on trunk. Rx: Antihistaminics, steroids and at times UVA therapy may be needed.DiseaseClinical featuresEtiologic agentImpetigoHoney-colored crusted papules, plaques, or bullaeGroup A streptococcus and Staphylococcus aureusDermatophytosisInflammatory or noninflammatory annular scaly plaques; may have hair loss; groin involvement, spares scrotum; hyphae on KOH preparationTrichophyton, Epidermophyton, or Microsporum sp.CandidiasisInflammatory papules and plaques with satellite pustules, frequently in intertriginous areas; may involve scrotum; pseudohyphae on KOH preparationCandida albicans other Candida speciesTinea versicolorHyper- or hypopigmented scaly patches on the trunk; characteristic mixture of hyphae and spores spaghetti and meatballs on KOH preparationMalassezia furfur 