Linear porokeratosis.

Linear porokeratosis is a rare variant. It can be present at birth or can develop in adult life. Lesions of linear porokeratosis are grouped and linearly arranged along the lines of Blaschko. On the extremities it affects the distal portion more than the proximal areas. On the trunk these can be zosteriform in distribution. Lesions of linear porokeratosis probably result from an abnormal clone of epidermal precursors. A 20 year old male presented with annular plaques in linear pattern following the lines of Blaschko over the left upper limb extending up to the axilla present since childhood. The lesions had atrophic centre and raised hyperkeratotic borders. The lesions were more proximal than distal. Few scattered lesions were present on left side of trunk. There was no family history of such lesions. Systemic examination of patient was normal. On histopathological examination there was hyperkeratosis and parakeratosis. A coronoid lamella was present. At the base of coronoid lamella thinned out granular layer and necrotic keratinocytes were also seen. In the dermis pigment incontinence and perivascular lymphocytic infiltrate were present. This case is being reported because of its rarity. It is an atypical presentation because the lesions were disposed more over proximal than distal area of upper limb. Linear porokeratosis is associated with an increased risk of malignant transformation.