Beyond Nature’s Path: A Case of Unilateral Lichen Planus Pigmentosus along Blaschko’s Line

An 11-year-old girl presented with pruritic, dark brown linear pigmentation over her left leg for three years. The lesions began as asymptomatic macules and gradually extended from the ankle to the inguinal fold along Blaschko’s lines. There was no preceding erythema, trauma, or drug exposure. On examination, violaceous to brown confluent macules in a unilateral blaschkoid pattern were observed extending from the left ankle to the inguinal fold [Figure 1a]. Dermoscopy showed brown to black dots and globules interspersed with white eccrine openings [Figure 1b]. Histopathology revealed epidermal thinning, basal cell degeneration, numerous melanophages, and pigment incontinence, consistent with lichen planus pigmentosus (LPP) [Figure 1c]. The patient responded partially to topical corticosteroid and tacrolimus.Figure 1: (a) Irregular well to ill-defined violaceous to dark brown confluent macules arranged in a unilateral, blaschkoid distribution were observed extending from the left medial ankle to the left inguinal fold. (b) Dermoscopy revealed brown, brownish-black dots and globules (due to pigment incontinence) interspersed with white dots representing the normal eccrine openings. (c) Histopathology showing hyperkeratosis, epidermal thinning, vacuolar degeneration of the basal cell layer (blue asterix), plenty of melanophages (black arrow), and lymphohistiocytic infiltrate in superficial dermis and perivascular location (green circle) on H and E section (×40 view)LPP is an uncommon variant of lichen planus, usually seen in adults and rarely reported in children. Linear LPP, a rare subtype, follows Blaschko’s lines and may result from cutaneous mosaicism or immune-mediated responses.[1,2] Reported triggers include sun exposure and topical agents. Management involves topical corticosteroids, calcineurin inhibitors, and photoprotection, while low-dose oral isotretinoin has shown benefit in stabilizing pigmentation.[3] This case highlights an uncommon pediatric presentation of linear LPP along Blaschko’s lines, underscoring the need to differentiate it from linear lichen planus, epidermal nevus, and postinflammatory hyperpigmentation. Declaration of patient consent The authors certify that they have obtained all appropriate consent forms, duly signed by the parent(s)/guardian(s) of the patient. In the form, the parent(s)/guardian(s) has/have given his/her/their consent for the images and other clinical information of their child to be reported in the journal. The parents understand that the names and initials of their child/children will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.