Cutaneous immunocytomas: a clinicopathologic study of 26 cases

The clinical and histological features of 16 patients with a primary cutaneous immunocytoma and 10 patients with a secondary cutaneous immunocytoma are reported. In all cases the diagnosis was based on the presence of monotypic plasma cells or lymphoplasmacytoid cells. Our data show that primary cutaneous immunocytomas are a distinct type of cutaneous lymphoma, characterized by (a) the presence of solitary or localized skin lesions (13 of 16 cases); (b) preferential localization on arms and legs (15 of 16 cases); (c) excellent response to local treatment (15 of 16 cases) and (d) a favourable prognosis. Histologically, these primary cutaneous immunocytomas are characterized by the presence of nodular or diffuse infiltrates with monotypic lymphoplasmacytoid/plasma cells located at the periphery of the infiltrates. Important clinical and histological differences were noted between primary and secondary immunocytomas. In the latter group more widespread skin disease was seen, often in the presence of paraproteins and/or autoimmune diseases. In contrast with the peripheral localization of the monotypic cells in primary cutaneous immunocytomas the monotypic lymphoplasmacytoid/plasma cells in secondary immunocytomas formed diffuse infiltrates or these cells were found dispersed throughout the infiltrate. There were no differences in clinical presentation or course between the different subtypes of cutaneous immunocytomas (lymphoplasmacytic, lymphoplasmacytoid and polymorphic immunocytomas). The differential diagnosis between primary cutaneous immunocytomas and cutaneous plasmacytomas, primary follicular centre cell lymphomas and cutaneous 'pseudolymphomas' is discussed.