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?

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 distribution)Wickham 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 - ulcerative/erosive 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 areata)Classical/characteristic nail finding (but not common finding)- pterygium formation (proximal nail fold fuses with nail bed)Hair follicles: lichen pktnopilaris - scarring alopeciaHistopathology:HyperkeratosisWedge shaped hypergranulosis (psoriasis - hypogranulosis)Irregular acanthosis (psoriasis - regular acanthosis)Saw tooth rete ridges (psoriasis - elephant foot/camel foot like/club 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 zone)Melanin incontinenceTreatment - steroids (topieal/intralesionsal/ systemic), retinoids, cyclosporine, PUVA photochemotherapy, dapsone, methotrexateLichen planus- "8 P's"Papu losq uamous disorderPruriticPlane toppedPolygonal/polyangularPurple colouredPapulesPlaquesPigmentation after healing Pterygium formation in nails