Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (378 page)

   Test no longer recommended: serum immunoelectrophoresis.

Suggested Readings

Bergsagel PL, Mateos M-V, Gutierres NC, et al. Improving overall survival and overcoming adverse prognosis in the treatment of cytogenetically high-risk multiple myeloma.
Blood.
2013;121:884–892.

Kyle RA, Rajkumar SV. Multiple myeloma.
Blood.
2008;111:2962–2972.

MONOCLONAL GAMMOPATHY OF UNDETERMINED SIGNIFICANCE (MGUS)

   Definition

MGUS is an asymptomatic preneoplastic condition characterized by the presence in the serum of

   Monoclonal (M)-protein, but <3 g/dL

   Bone marrow clonal plasma cells <10%

   No lytic lesions, anemia, hypercalcemia, or renal insufficiency (see below), that is, no end-organ damage that can be attributed to the plasma cell proliferative disorder. A special situation was recently discussed: monoclonal gammopathies associated with kidney disease and the term “monoclonal gammopathy of renal significance” was proposed.

   No clinical manifestations or evidence of another B-cell proliferative disorder.

In most cases, neoplastic plasma cells are present in the bone marrow; however, clonal IgM-producing cells may be seen originating in the spleen and lymph nodes. The risk of progression to an overt plasma cell myeloma, amyloidosis (), lymphoplasmacytic lymphoma , or other lymphoproliferative disorder is 1% per year. MGUS patients with abnormal free light chain ratio are at high risk of developing amyloidosis. MGUS has been divided into three subtypes with different modes of progression: non-IgM MGUS, the most prevalent, IgM-MGUS, and light chain MGUS.

   Who Should Be Suspected?

MGUS is more common in men (1.5:1) and African American subjects; its incidence is 4.2% in individuals older than 50 years and 5% in those older than 70. There are no distinctive symptoms or physical findings associated with this disorder. Seventy-nine percent to 82% of patients with the systemic capillary leak syndrome have MGUS.

   Laboratory Findings

   Bone marrow biopsy and aspirate. Plasma cells are increased, but <10; interstitial and in small cluster distribution.

   CBC is usually normal. Rouleaux formation (due to paraproteinemia) may be seen.

   Serum proteins may be elevated with increased globulins (decreased A:G ratio) and hypoalbuminemia.

   Hypogammaglobulinemia may be present in light chain MGUS where only light chains are produced.