Free Immunoglobulin Light Chains in Patients With Myocarditis: a New Biomarker of Inflammation and Heart Failure

AIM: To study the concentration of immunoglobulin free light chains (FLCs) in patients with myocarditis in comparison with non-inflammatory heart diseases, their relationship with inflammatory markers and the severity of chronic heart failure (CHF). MATERIAL AND METHODS: This study included 77 patients (31 women, mean age 54.1±13.3 years): 41 patients with myocarditis verified by myocardial biopsy (n=18) or using a noninvasive diagnostic algorithm, 31 patients with noninflammatory CHF (comparison group), and 5 patients with monoclonal gammopathy identified during the study (4 of them were diagnosed with AL amyloidosis with heart damage). In the myocarditis group, CHF was diagnosed in 29 patients, mean stage IIA, functional class (FC) 2-3, with a mean left ventricular ejection fraction 43%. In the comparison group, patients had predominantly IIA stage, FC 2-3 CHF without systolic dysfunction. The blood concentration of kappa and lambda FLC types was measured with Cloneus S-FLC-K TIA Kit and Cloneus S-FLC-L TIA Kit. Concentrations were considered normal at FLC-kappa 4.84-14.20 mg/l, FLC-lambda 7.03-22.50 mg/l, and the FLC-kappa/lambda ratio 0.426-1.050. RESULTS: Increased FLC concentrations were found in 58% of patients with myocarditis and in 77% of patients in the comparison group. The FLC-lambda concentration was significantly higher in the comparison group; there were no significant differences between the groups in FLC-kappa and their ratio. The closest significant correlations in both groups and the entire cohort were noted between FLCs of either type and CHF, as well as the requirement for loop diuretics (correlation coefficients, 0.60-0.90), independent on the severity of systolic dysfunction. Myocarditis patients also showed correlations of FLCs with the titer of antibodies to cardiomyocyte nuclear antigens, levels of C-reactive protein, leukocytes, neutrophils, erythrocyte sedimentation rate, and the concentration of N-terminal fragment of brain natriuretic peptide. In a subgroup of 10 myocarditis patients who were treated with immunosuppressants, FLCs of both types were significantly lower than in the comparison group; only with the persistence of severe CHF was an increase in FLCs noted. CONCLUSION: An increased FLC concentration can be considered as an important pathogenesis component that reflects both the specific mechanisms of myocarditis and the severity of CHF. In the absence of a statistically significant increase in general inflammatory markers in the blood of myocarditis patients, the measurement of FLCs can be used as an additional diagnostic marker and predictor of the decompensated variant of the course of myocarditis. However, the diagnostic and prognostic significance of FLC concentration in patients without CHF requires a further study.