Primary cutaneous immunocytoma. A B-cell lymphoma that can easily be mistaken for cutaneous lymphoid hyperplasia.

It has been estimated that immunocytomas comprise roughly 2% of all cutaneous lymphomas. We studied five patients with primary cutaneous immunocytomas who presented with cutaneous nodules or plaques. Many of the infiltrates were "top-heavy" and polymorphous with admixed eosinophils, macrophages, lymphoid follicles, and non-neoplastic lymphocytes. Other potentially confusing findings were one case each of spongiotic dermatitis and leukocytoclastic vasculitis. The neoplastic cells were often situated at the peripheries of nodules and ranged from those with nuclei that resembled small lymphocytes to others that resembled immunoblasts. Most had eccentrically placed nuclei and fan-shaped cytoplasm. Monotypic kappa-light chain was found in all five cases, accompanied by gamma-heavy chain in two cases, and mu-heavy chain in one. In situ hybridization detected only kappa-mRNA in the four cases that yielded technically satisfactory results. The neoplastic cells did not express the B-cell antigen CD20; T-cells formed the centers of many nodules. Inappropriate staining for CD43 was evident in the neoplastic cells of one case. Because of reports of immunocytomas complicating acrodermatitis chronica atrophicans, we stained sections with an antiserum to Borrelia burgdorferi, which did not detect that organism. In situ hybridization did not detect EBER-1 RNA of the Epstein-Barr virus, which can be present in immunocytomas in immunocompromised patients. One patient died of disease after failing chemotherapy; another is alive with disseminated disease, and three are in remission following excision of lesions alone in two patients and chemotherapy in one patient who had relapsed following both excision and radiation therapy.