case_images: PMC11815510_01
case_images: Pink lichenoid plaques with thick yellow adherent keratotic nodules and background erythema on the bilateral legs consistent with hypertrophic lichen planus and possible keratoacanthoma or squamous cell carcinoma.
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case_images: Differential diagnoses included hypertrophic LP and possible KA or SCC (Fig 1).
case_images: A and B, Crateriform squamous proliferation with abundant keratin and associated lymphocytic inflammation consistent with a keratoacanthoma, a well-differentiated squamous cell carcinoma, or hypertrophic lichen planus at the specimen's periphery (H&E, 2x).
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case_images: Shave biopsies from the right leg 2 months prior demonstrated the surface of an atypical squamous epithelial proliferation and atypical endophytic squamous proliferation consistent with either a KA, a well-differentiated SCC, or hypertrophic LP at the specimen's periphery (Fig 2, A and B).
case_images: Marked improvement in keratoacanthoma appearance after 5-fluorouracil treatment with residual erythema and a few thick yellow adherent keratotic nodules on the bilateral legs.
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case_images: This prompted treatment of the remaining KAs with 3 total injections of intralesional 5-fluorouracil 50 mg/mL which all regressed (Fig 3).