Pagetoid reticulosis in a 5-year-old boy.

We present a rare case of pagetoid reticulosis arising in a 5-year-old white boy. He had a history of a large chronic erythematous, scaly patch on his left buttock that had shown intermittent partial response to a topical antifungal medication. A punch biopsy specimen revealed dramatic epidermal hyperplasia, with parakeratosis and prominent exocytosis of single and clustered mononuclear cells (Pautrier's microabscesses) into the epidermis. Some of these exhibited hyperchromatic nuclei with irregular contours. They stained prominently for CD3, CD4, and CD8, with a predominance of CD8(+) cells. T-cell receptor gene rearrangement by polymerase chain reaction was negative for a clonal process on a second biopsy specimen that was nondiagnostic on routine sections. Pagetoid reticulosis is an indolent, unilesional variant of mycosis fungoides, in which the atypical T cells may express a CD4(-)/CD8(+) phenotype. This is in contrast to primary cutaneous epidermotropic CD8(+) cytotoxic T-cell lymphoma, which is often very aggressive with a poor outcome. Pagetoid reticulosis is exceedingly rare in children and adolescents. Two features predict a benign course in this 5-year-old child: the unilesional clinical presentation and the CD8 predominance of the epidermal lymphocytes.