<prompt> A young lady presents with white lacy lesions in oral cavity and her proximal nail fold has extended onto the nail bed. What is the likely diagnosis?PsoriasisGeographic tongueLichen planusCandidiasis  <response>: Ref: Papulosquamous Disorders. In: Thappa DM. editor. Essentials in Dermatology, 2nd edn., NewDelhi: Jay pee Brothers Medical Publishers P Ltd 2009:82-98.Explanation:LICHEN PLANUSIt is a pruritic, inflammatory papulosquamous disorder affecting the skin, mucous membranes, nails and hair follicles.Etiology - UnknownGenetic predisposition: HI A B8- oral LP: HLA-Bw 35-cutaneous LPExogenous: Primary biliary cirrhosis, alcoholic cirrhosis, hepatitis B, hepatitis CDrugs cause lichenoid drug eruptionsMetals like mercury dental amalgams, palladium, gold - oral lichenoid eruptionsClinical features:30-60 years; children -4 of cases, childhood LP more common in India 05 SkinIntensely pruritic, flat topped, shiny, polygonal, violaceous papules and plaquesPredominantly flexor distribution - flexor of wrist, forearm, legs, trunk, glans penis cf- psoriasis another papulosquamous disorder has predominant extensor distributionWickham fs striae- netw-ork of greyish w hite streaks on papules seen on pressing with glass slide after application of oil - corresponds to wedge shaped hvpergranulosis seen on histo-pathologyKoebner! isomorphic phenomenon commonAnnular LP- glans penisHypertrophic LP- shinsActinic LP-sun exposed areasOral:Classical type is reticulate pattern- white violaceous lacy reticular network of coalesent papules in buccal mucosa and tongue; usually asymptomaticMost common pattern - ulcerativeerosive LPNail:5-10 casesThinning of nail plate cf psoriasis - thickening of nail plate, longitudinal ridging, roughening of nail plate trachyonychia and nail dystrophy involving all 20 nails called 20 nail dystrophy also seen in alopecia areataClassicalcharacteristic nail finding but not common finding- pterygium formation proximal nail fold fuses with nail bedHair follicles: lichen pktnopilaris - scarring alopeciaHistopathology:HyperkeratosisWedge shaped hypergranulosis psoriasis - hypogranulosisIrregular acanthosis psoriasis - regular acanthosisSaw tooth rete ridges psoriasis - elephant footcamel foot likeclub shaped rete ridges Basal layer vacuolar degenerationBand like dermal lymphocytic infiltrate hugging epidermisMax Joseph spaces - subepidermal clear zone subepidermal clear zone in lepro- matous leprosy is called Grenz zoneMelanin incontinenceTreatment - steroids topiealintralesionsal systemic, retinoids, cyclosporine, PUVA photochemotherapy, dapsone, methotrexateLichen planus- 8 PsPapu losq uamous disorderPruriticPlane toppedPolygonalpolyangularPurple colouredPapulesPlaquesPigmentation after healing Pterygium formation in nails 