The most characteristic finding in lichen planus is-

LICHEN PLANUS:-Inflammatory T cell mediated auto immune disorder affecting skin, hair,nails and mucous membranes.Four P s- purple , polygonal pruritic papule. clinical features: skin lesions- erythematous to violaceous, flat topped, polygonal papules. most common sites- flexors of wrist , lumbar,ankle region oral cavity-erosive or ulcerative leions on mucosa with violaceous hue. koebners phenomenon-present wickham straie: fine white reticulate pattern seen in old lesions. nails- fine pitting, PTERYGIUM morphological variants: 1: classical- most common 2: hyperophic 3: atrophic 4:guttate 5: annular 6:linear 7: bullous 8:ulcerative 9: lichenplanus pigmentosus Histology:-1. Irregular acanthosis of the epidermis.2. Hypergranulosis 3. Compact hyperkeratosis.4. Basal cell degeneration.5. Colloid bodies6. Pigment incontinence.7. Band like lympho histiocytic infiltrate obscuring the dermoepidermal interface. 8.rete ridges flat- SAW TOOTH APPEARENCE Reference: IADVL textbook of dermatology page-1077