Paraproteinemia

Paraproteinemia is the presence of a monoclonal immunoglobulin, or M-protein, in the blood or urine. It is produced by a single clone of B cells or plasma cells and is detected by serum protein electrophoresis and immunofixation to determine the isotype and light-chain type. Paraproteinemia describes a laboratory finding that can occur in a spectrum of conditions, from benign states to malignant plasma cell or lymphoid disorders.

Common causes include monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma, Waldenström macroglobulinemia, light-chain amyloidosis, and various lymphoproliferative diseases. Paraproteins may be whole immunoglobulins (IgG, IgA, IgM) or free light chains (kappa or lambda). The presence and type of the paraprotein help guide diagnosis and management, but the finding alone does not establish a specific disease.

Clinical features vary. Many individuals are asymptomatic and the paraprotein is found incidentally. Symptoms or complications can arise from the underlying disorder or from the physicochemical effects of the paraprotein, such as hyperviscosity with IgM, renal impairment from light chains, peripheral neuropathy, or amyloid-related organ damage.

Diagnosis typically starts with serum protein electrophoresis, followed by immunofixation to type the M-protein. Quantitative immunoglobulins, serum free light-chain assay, and urine studies for Bence Jones proteins are used. If a clonal hematologic disorder is suspected, bone marrow biopsy and imaging for organ or bone involvement are performed.

Management targets the underlying condition. MGUS is usually monitored without treatment, as progression to multiple myeloma or related disorders occurs at a low annual rate. Paraproteinemias causing hyperviscosity, renal disease, neuropathy, or amyloidosis require disease-specific interventions, including plasmapheresis in acute settings.