Multicenter Descriptive Study of Monoclonal Gammopathy of Undetermined Significance in Patients with Heart Failure

Introduction: Monoclonal gammopathy of undetermined significance (MGUS) is the presence of a monoclonal immunoglobulin without concurrent lymphoproliferative disease. It is found in about 5% of people aged 50 and older in the general population. Prevalence rates of MGUS increase with age, especially in men and individuals of Black ethnicity compared to women and White individuals, respectively. The diagnostic criteria for MGUS includes a serum M-protein level <3 g/dL, <10% clonal plasma cells in the bone marrow, and the absence of a myeloma-defining event. Though historically considered benign, emerging evidence suggests that MGUS patients, even without lymphoproliferative disorders, face increased risks of various diseases like bone diseases, recurrent infections, autoimmune disorders, peripheral neuropathy, renal complications, and cardiovascular disease (CVD). This study aims to investigate the prevalence and characteristics of individuals with both MGUS and heart failure (HF) and examine potential racial disparities between Black patients and non-Black patients with MGUS and HF.

Methods: This is a retrospective multicenter study that includes patients diagnosed with both MGUS and New York Heart Association grade II or higher HF from January 2010 to January 2023. Patients with potential confounding conditions of MGUS were excluded, such as non-MGUS plasma cell dyscrasias, hematologic malignancies, autoimmune/inflammatory disorders, and viral illnesses. Laboratory data was recorded at the time of MGUS diagnosis, and HF data was derived from imaging studies performed closest to the time of MGUS diagnosis or at the initial diagnosis of HF if it was diagnosed after MGUS. Findings were summarized using descriptive statistics.

Results: We analyzed a total of 128 patients with MGUS and HF, excluding 24 patients with potential MGUS confounders. Among the remaining 104 patients, 41 (39.4%) were female, and 63 (60.6%) were male. The cohort consisted of 80 (76.9%) Black patients and 24 patients of non-Black ethnicity. For the overall cohort, the mean age at MGUS diagnosis was 72, and the mean time from HF diagnosis to MGUS diagnosis was 22.5 months with a median of 9.1 months. In 24% of patients, HF and MGUS were diagnosed within less than 1 month of each other. The predominant monoclonal proteins observed were IgG Kappa, IgG Lambda, and IgA Kappa, found in 54 (51.9%), 30 (28.8%), and 13 (12.5%) patients, respectively. The average M spike was 0.7 +/- 0.6 (SD, standard deviation), and the average free light chain ratio was 2.3 +/- 2.3 (SD). The most common type of HF diagnosed was heart failure with reduced ejection fraction (HFrEF, EF <40%), occurring in 63.5% of the cohort. The etiology of HF in the cohort was attributed to ischemic cardiomyopathy in 43.3%, non-ischemic cardiomyopathy in 51%, and a combination of both in 5.7%. Table 1 presents the MGUS variables for the overall cohort and stratification by race. Table 2 displays the characteristics of study subjects based on the type of HF, including HFrEF, mid-range ejection fraction (HFmrEF, EF 40-49%), and preserved ejection fraction (HFpEF, EF >50%).

Conclusion: This study did not find a significant association between MGUS variables and HF, likely due to the limited sample size. However, a larger study by Schwartz et al. using a Danish nationwide database with over 8,000 participants suggested that MGUS patients had a higher risk of incident CVD, even after adjusting for other comorbidities. They also noted a higher prevalence of CVD risk factors in patients with MGUS. These findings indicate a possible link between MGUS and CVD, though the true nature of this association remains uncertain - whether it's causal or coincidental. An interesting observation from our study is that MGUS is often incidentally detected in patients already diagnosed with HF. This suggests that physicians may come across MGUS while investigating the underlying causes of HF, raising the possibility of shared underlying factors or pathological processes between both conditions. Considering our findings, it's essential to recognize that MGUS patients may have a higher mortality risk independent of developing plasma cell disorders. Large-scale studies are needed to better understand the association between MGUS and CVD, potentially influencing monitoring and follow-up strategies for MGUS patients, especially concerning potential cardiovascular implications.