Cutaneous pseudolymphoma is a benign reactive lymphoproliferative skin disorder that can mimic cutaneous lymphoma. Clinical features include papules or indurated plaques that commonly affect the head and neck region and upper extremities. Various causative factors such as infectious agents, insect bites, vaccines, foreign bodies such as tattoos and drugs have been identified. Majority of the cases are idiopathic. Diagnosis is made by clinical assessment and careful histopathologic examination. Topical or intralesional steroids are the first-line therapy for persistent localized lesions.

This is a case of a 14-year-old male who presented with an 8-month persistent solitary violaceous to dusky red indurated plaque on the right distal ventral forearm. No trigger factors were identified. A skin biopsy with immunohistochemical staining (positively staining CD68, CD3 and CD20 T and B cells with no loss of CD7) revealed cutaneous lymphoid hyperplasia. Initial treatment with a topical steroid was unsuccessful, leading to the addition of intralesional steroid to the regimen. This resulted in partial improvement but did not prevent further plaque enlargement. Topical medication was then shifted to compounded 5-Fluorouracil cream which was applied twice daily for a duration of 18 months. In the first six months of treatment, the patient noted further decrease in size and flattening of the lesion with no reported adverse effects. A repeat biopsy after 18 months post- treatment revealed a marked reduction in lymphocytic infiltrates, indicating a favorable response to treatment.

The main goal of treatment in Cutaneous Pseudolymphoma is early disease recognition and prompt intervention. Topical 5- fluorouracil (5-FU) belongs to a class of medications known as anti-metabolites and has been used in the treatment of various recalcitrant benign and malignant skin tumors. Treatment efficacy of this case contributes to anecdotal evidence of topical 5-Fluorouracil in treating pseudolymphoma.