Papules in a blaschkoid distribution on the thigh

We present two cases of inflammatory dermatoses following Blaschko's lines on the thigh. The first case presented with pruritic violaceous papules with comedone-like openings, diagnosed as hypertrophic lichen planus. The second case developed linear hyperpigmented papules and plaques, diagnosed as lichen striatus. Both conditions presented similarly in their blaschkoid distribution but were differentiated through integrated clinico-dermoscopic-histopathological correlation. Dermoscopy revealed follicular plugs with blue-grey globules over a purple background in hypertrophic lichen planus, while lichen striatus showed patchy dotted vessels with white areas and erosions. Histopathologically, follicular involvement and melanophages characterised hypertrophic lichen planus, whereas deep peri-eccrine lymphocytic infiltrates were distinctive for lichen striatus. This report highlights the diagnostic utility of dermoscopy in differentiating clinically similar blaschkoid dermatoses.