Clinical Characteristics of Hyposecretory Multiple Myeloma (Monoclonal Immunoglobulin < 3 g/dl) in Afro-Caribbean Patients at a Single Urban Institution

Introduction

Monoclonal gammopathy of undetermined significance (MGUS) is defined as the presence of monoclonal immunoglobulin (Ig), without the diagnosis of multiple myeloma (MM), while the diagnosis of MM requires the presence of a monoclonal immunoglobulin (Ig) ≥ 3g/dl or Bence-Jones protein (BJP) ≥ 500mg/24h, with bone marrow involvement of greater than 10% clonal plasma cells.

Kings County Hospital (KCH) is an institution that serves a large population of Afro-Caribbean population. In our institution, an increased number of patients were observed to present with MM with monoclonal Ig <3g/dl but yet have end organ damage. The clinical characteristics of Afro-Caribbean population have not been well studied and further characterization may have diagnostic implications.

Methods

This is a retrospective study conducted at KCH. Data regarding the clinical profile of patients diagnosed with MM from 2000- 2013 was collected from the institution's tumor registry. Patients with monoclonal Ig < 3g/dl and BJP <500mg/24h were analyzed and compared to standard MM patients with monoclonal Ig ≥ 3g/dl or BJP ≥ 500mg/24h. Data was collected for lab parameters which included quantity and type of monoclonal Ig, serum free light chains and ratio, monoclonal plasma cell percentage in the bone marrow, International staging system (ISS) stage, cytogenetics, presence of anemia, hypercalcemia, renal failure and lytic lesions. Epidemiologic parameters age and gender were also collected. Results were analyzed by a Chi-square test to calculate a mid-P exact.

Results

A total of 287 patients with MM were screened, of which 56 patients with incomplete electronic records were excluded. Of the remaining 231 patients, 63 (27%) had monoclonal Ig <3 g/dl without the presence of BJP ≥ 500mg/24h. These patients were labeled hyposecretory MM. 168 (73%) patients had standard MM, with monoclonal Ig ≥ 3g/dl or BJP ≥ 500mg/24h. In the hyposecretory MM group, 35% of patients presented with International staging system (ISS) stage I vs. 13% in the standard MM group (P= 0.0001). IgG monoclonal Ig was present in 75% of patients with hyposecretory MM compared to 62% in the standard MM group (P=0.04). Mean plasma cell percentage in the bone marrow was similar in both groups, 40% in the hyposecretory MM group compared to 51% in standard MM.

Average age of presentation was 64 yrs in the hyposecretory MM group as compared to 63 yrs in the standard MM group. There were more females than males in both groups, 61% females in hyposecretory MM and 53% in standard MM group.

The most common presenting symptom was anemia in both groups and there were no statistically significant differences noted in gender, presence of hypercalcemia, presence of bone lesions, and renal dysfunction. Cytogenetic data was insufficient.

Conclusion

In our study, a substantial number of Afro-Caribbean patients with low levels of serum monoclonal Ig without the presence of Bence-Jones protein were diagnosed with active multiple myeloma. The results of our study underline the importance of an aggressive diagnostic approach with a bone marrow biopsy at initial presentation with MGUS in Afro-Caribbean population. This may prevent disease progression and end organ damage.

Unlike the general population with MM, there were more females.