[Increasing anaplasia of an extramedullary plasmacytoma with loss of detectable paraproteinemia (author's transl)].

An epipharyngeal solitary extramedullary plasmacytoma with subsequent dedifferentiation is described. Immunohistochemically the plasmacytoma cells of the first biopsy were positive for lambda and gamma, immunoelectrophoretically only lambda was demonstrable. Three months later an anaplastic tumor reappeared whose cells were also immunohistochemically positive for lambda and gamma. However, paraproteins were no longer demonstrable in serum and urine. The observed changes were interpreted as a result of anaplasia. Furthermore, our case shows that the diagnosis of multiple myeloma is not always possible by means of immunoelectrophoresis. The most important implication of our case is the fact that a follow-up of serum or urine concentrations of paraproteins may not reflect the course of a given plasmacytoma.