IgD-λ multiple myeloma with excessive excretion of free light chains: a diagnostic trap in the identification of monoclonal gammopathies.

Immunoglobulin D multiple myeloma (IgD MM) is a rare entity of monoclonal gammopathies. We report the case of a IgD MM, associated with excessive excretion of lambda free light chains (FLL λ) diagnosed and managed at the University Hospital Mohammed VI of Marrakech among an adult hospitalized in the hematology department for bone pain and alteration of the general condition. Indeed, IgD MM is characterized by its clinical severity and poor prognosis. The discretion or absence of a monoclonal peak in the electrophoresis of serum proteins makes detection difficult. The present case demonstrates that IgD MM may be associated with excessive production of CLL and may therefore be erroneously diagnosed as CLL MM. Knowledge of this rare subtype of MM and its epidemiological, clinical and especially biological characteristics is crucial for establishing the correct diagnosis.