ABSTRACT
The diagnosis of multiple myeloma (MM) is based on the presence of bone marrow (BM) infiltration by plasma cells, together with a serum and/or urine monoclonal component and lytic bone lesions. Although the presence of clinical symptoms, such as bone pain, anemia, and renal insufficiency, may herald the diagnosis of MM, there are many cases in which the initial finding is limited to the presence of a high erythrocyte sedimentation rate or an M-component detected in an otherwise asymptomatic patient. The main challenge at diagnosis is to distinguish active MM, which requires treatment, from monoclonal gammopathies of undetermined significance (MGUS) and indolent myeloma, which do not. In addition, there are some forms of plasma cell dyscrasias (PCD) that may require specific diagnosis and treatment. In the following pages, we will first review the diagnostic criteria of MM and related disorders, with particular emphasis on those in which differential diagnosis is problematic.
