Post-thymic CD4 positive cytotoxic T cell infiltrates of the skin: A clinical and histomorphologic spectrum of the unique CD4 positive T cell of immunosenescence

T cell lymphoproliferative disorders that arise in the skin are mainly derived from post thymic T cells most commonly of CD4 subset. Human CD4 positive T cells are dynamic exhibiting phenotypic and functional malleability. For example, with repetitive antigen exposure most commonly associated with age, CD4 positive T cells acquire a cytotoxic phenotype. The authors present four cases characterized by cutaneous infiltrates of cytotoxic CD30 negative CD4 positive T cells in the skin; three cases were forms of malignant lymphoma other than mycosis fungoides and one case was a reactive lymphomatoid photodermatosis associated with underlying collagen vascular disease. The three patients with lymphoma were adult men, two above 50 years of age and all with disseminated cutaneous disease. One of these patients whose biopsy showed a large cell morphology succumbed to the disease while one patient with localized disease responded to local radiation. In all three cases there was a nodular and diffuse pan-dermal infiltrate which was predominated by non-cerebriform atypical lymphocytes ranging from small to intermediate sized cells in two cases to a large cell dominant morphology in one case. The biopsies showed some degree of epidermotropism, and in one case it was striking. Neoplastic cells were positive for CD4, and at least one cytotoxic protein (i.e. granzyme and/or TIA). CD56, CD57 or CD30 were negative. In addition, CD28, the naïve T cell marker, was negative. Based on the few cases reported herein, one might suggest that the prognosis mirrors that seen in other forms of cutaneous T cell lymphoma with mature small cell dominant infiltrates exhibiting an indolent pattern while a CD30 negative large cell T cell lymphoma would be expected to demonstrate an aggressive clinical course.