Abstract
A 59-year-old African American female presented with a three-month history of dark brown macules coalescing into linear streaking patches on her abdomen, chest, and back in a Christmas tree pattern. She also had 2 larger brown square patches on her abdomen and shiny lichenoid-appearing papules in clusters on her arms and abdomen. The rash was pruritic, and she denied any inciting events. The rash was initially diagnosed as pityriasis rosea by her primary care doctor, but her rash was worsening with subsequent referral to dermatology. Shave biopsies from the right arm, back and abdomen all showed the histopathologic reaction pattern of post-inflammatory hyperpigmentary alteration, which can follow most any type of interface dermatitis. Fortunately, the histopathology from the right abdomen biopsy also showed a focus with features typical for lichen planus including vacuolar alteration with clefting at the dermal-epidermal junction, squamatization of the basilar layer, and overlying wedge-shaped hypergranulosis. The subjacent underlying dermal inflammatory infiltrate was predominantly lymphocytic with intermixed scattered melanophages. A diagnosis of lichen planus pigmentosus (LPP) was made. LPP is an uncommon variant of lichen planus that usually presents with asymptomatic macules and patches in a linear, blaschkoid, perifollicular, or reticular pattern. To date, LPP has not been reported in a Christmas tree pattern (the thoracodorsal expression of Langers lines), which is more commonly seen in conditions such as pityriasis rosea, mycosis fungoides, and syphilis. Skin diseases following this pattern seem to involve the hematogenous dissemination of activated leukocytes, which is consistent with this presentation.3 We present an unusual clinical presentation of LPP in a Christmas tree pattern that is pathologically distinct from associated differential diagnoses such as pityriasis rosea, requiring an alternative treatment course for optimal clearance.
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