[Lymphoplasmacytic lymphoma or multiple myeloma: immunoglobulins may lead to misdiagnosis]. / Lymphome lymphoplasmocytaire ou myélome multiple : quand les immunoglobulines induisent en erreur.

We report here a case of lymphoplasmacytic lymphoma with IgA paraproteinemia and a case of concomitant Waldenström macroglobulinemia and monoclonal gammapathy of unknown significance. These rare cases show that the isotype of a monoclonal immunoglobulin does not allow to foresee every time the underlying pathology. Clinical data and medical imaging are essential. From a biological point of view, additional analysis such as immunophenotyping, cytogenetics and molecular biology are required in addition to the cytological features in order to make an accurate differential diagnosis between lymphoid and plasma cell malignancy.