Gammapatías biclonales: estudio retrospectivo de 47 pacientes

Biclonal Gammopathies in South Tunisia: Clinical and Biological Characteristics

OBJECTIVE

Biclonal gammopathies (BGs) are rare situations characterized by the production of 2 monoclonal proteins. There are no available data on BGs in North Africa. We aimed to estimate the prevalence of BGs in our population and describe their clinical and laboratory features.

METHODS

We conducted a 31-year retrospective study including patients with persistent double monoclonal bands based on the results of immunofixation/immunoelectrophoresis.

RESULTS

A total of 35 patients with available clinical data (sex ratio, M/F = 1.53; mean age, 70 ± 10.87 years [range, 45-90 years]) were included. The main associated conditions were multiple myeloma (MM) (40%), BG of undetermined significance (BGUS) (34%), and lymphoproliferative diseases (23%). Only one-third of the patients had 2 monoclonal spikes on serum protein electrophoresis. The most common paraprotein combinations were immunoglobulin (Ig)G-IgG (25%) and IgG-IgA (23%) with different light chains in one-half of the cases. The mean follow-up was 25.6 months (median, 12 months). No BGUS evolved into a malignant disease.

CONCLUSION

BGs are rare in clinical laboratory routine but must be accurately identified by the pathologist. Our cohort is characterized by a high prevalence of BGUS compared with MM.

Detection of paraprotein in plasma cell tumors

Paraprotein is a laboratory biomarker of plasma cell tumors and other lymphoproliferative diseases. Its determination is necessary for diagnosing, monitoring and assessment of therapy effectiveness. The lecture presents the main methods of qualitative and quantative analysis of monoclonal proteins: gel electrophoresis, capillary electrophoresis, immunofixation and nephelometry features, possibilities and limitations are reviewed. The main sources of errors and artifacts during these studies are considered. Also the difficulties in the diagnosis and interpretation of the results of serum and urine tests are highlighted.

MALDI-TOF mass spectrometry can distinguish immunofixation bands of the same isotype as monoclonal or biclonal proteins

BACKGROUND

Plasma cell disorders (PCDs) are typically characterized by excessive production of a single immunoglobulin, defined as a monoclonal protein (M-protein). Some patients have more than one identifiable M-protein, termed biclonal. Traditional immunofixation electrophoresis (IFE) cannot distinguish if two bands of the same isotype represent biclonal proteins or M-proteins with some other feature. A novel assay using immunoenrichment coupled to matrix-assisted laser desorption ionization time-of-flight mass-spectrometry (Mass-Fix) was applied to determine whether two bands of the same isotype represented (1) monomers and dimers of a single M-protein, (2) an M-protein plus a therapeutic monoclonal antibody (t-mAb), (3) an M-protein with light chain glycosylation, or (4) two distinct biclonal M-proteins.

METHODS

Patient samples with two bands of the same isotype identified by IFE were enriched using nanobodies against IgG, IgA, IgM, or κ and λ light chains then analyzed by Mass-Fix. Light chain masses were used to differentiate IgGκ M-proteins from t-mAbs. Mass differences between peaks were calculated to identify N-glycosylation or matrix adducts. High-resolution mass spectrometry was used as a comparator method in a subset of samples.

RESULTS

Eighty-one residual samples were collected. For IgA, 93% (n = 25) were identified as monoclonal. For IgG, 67% (n = 24) were monoclonal, and 33% (n = 12) were truly biclonal. Among the monoclonal IgGs, the second band represented a glycosylated form for 21% (n = 5), while 33% (n = 8) had masses consistent with a t-mAb. 44% (n = 8) of IgM samples were biclonal, and 56% (n = 10) were monoclonal, of which one was glycosylated.

CONCLUSIONS

We demonstrate the utility of mass spectrometry in the characterization of multiple IFE bands of the same isotype. Improved reporting accuracy of M-proteins is useful for monitoring of patients with PCDs.

Demystifying Biclonal Gammopathy: A Pathologist’s Perspective

Background

The production of 2 monoclonal proteins characterizes biclonal gammopathic manifestations (BGMs). The available medical literature from India is chiefly restricted to case reports.

Objective

To study the incidence of BGMs in a tertiary care center in Chandigarh, India, during a 4-year period. We evaluated these cases further for their laboratory characteristics.

Methods

We scrutinized the contents of a database containing information from the studied 4-year period. Cases reported as BGMs on serum protein electrophoresis (SPEP) and confirmed by serum immunofixation electrophoresis (SIFE) were included.

Results

A total of 15 cases, from a cohort of 914 cases of monoclonal gammopathic manifestations (MGMs), were available. On SPEP, 2 M bands were observed in 12 cases. On SIFE, 4 cases were reported as being of true BGMs. The most common heavy-chain combination observed was immunoglobulin (Ig)A-IgG. Follow-up was available in 2 patients.

Conclusion

Identification of BGMs increases diagnostic precision, despite that the treatment is similar to that for monoclonal gammopathic manifestations (MGMs). BGMs can be transitory and may be observed at presentation or during the disease course.

Active multiple myeloma suppresses and typically eliminates coexisting MGUS

Background:

Myeloma is consistently preceded by premalignant monoclonal gammopathy of undetermined significance (MGUS). In >5% of MGUS patients there is a second MGUS clone (biclonal gammopathy of undetermined significance; BGUS), yet, at myeloma diagnosis, presentation of biclonal gammopathy myeloma (BGMy) is considered less frequent, implying that myeloma eradicates coexisting MGUS.

Methods:

In the largest study of its kind, we assessed BGMy frequency amongst 6399 newly diagnosed myeloma patients enrolled in recent UK clinical trials.

Results:

Compared to expected prevalence (i.e., >5% of MGUS have BGUS), only 58 of 6399 (0.91%) newly diagnosed myeloma patients had BGMy, indicating myeloma typically eliminates coexistent MGUS. In these 58 BGMy cases, the MGUS plasma cell clone was greatly suppressed in size compared to typical levels observed in conventional MGUS; contrarily, the MGUS clone did not inhibit the myeloma plasma cell clone in BGMy.

Conclusion:

Myeloma eliminates the majority of competing MGUS, and when it does not, the MGUS clone is substantially reduced in size.

Occurrence of Double Monoclonal Bands on Protein Electrophoresis: An Unusual Finding

Various techniques of protein electrophoresis are used for detection of monoclonal proteins/paraproteins in serum and/or urine of patients with monoclonal gammopathies. These are detected as the so-called 'M' bands (monoclonal bands) on serum protein electrophoresis and/or immunofixation electrophoresis. In most cases, a single M-band is detected. However, more than one M-band can be detected in the samples of a minor proportion of patients. This condition is termed as 'double gammopathy' or 'biclonal gammopathy'. A knowledge of such an unusual occurrence is essential for recognition and appropriate interpretation of this entity.