Infectious agents is a risk factor for myxomatous mitral valve degeneration: A case control study

Background The etiology of myxomatous mitral valve degeneration (MVD) is not fully understood and may depend on time or environmental factors for which the interaction of infectious agents has not been documented. The purpose of the study is to analyze the effect of Mycoplasma pneumoniae (Mp), Chlamydophila pneumoniae (Cp) and Borrelia burgdorferi (Bb) on myxomatous mitral valve degeneration pathogenesis and establish whether increased in inflammation and collagen degradation in myxomatous mitral valve degeneration etiopathogenesis. Methods An immunohistochemical test was performed to detect the inflammatory cells (CD20, CD45, CD68) and Mp, Bb and MMP9 antigens in two groups. The in situ hybridization was performed to detect Chlamydophila pneumoniae and the bacteria study was performed using transmission electron microscopy. Group 1 ( n = 20), surgical specimen composed by myxomatous mitral valve degeneration, and group 2 ( n = 20), autopsy specimen composed by normal mitral valve. The data were analyzed using SigmaStat version 20 (SPSS Inc., Chicago, IL, USA). The groups were compared using Student’s t test, Mann-Whitney test. A correlation analysis was performed using Spearman’s correlation test. P values lower than 0.05 were considered statistically significant. Results By immunohistochemistry, there was a higher inflammatory cells/mm2 for CD20 and CD45 in group 1, and CD68 in group 2. Higher number of Mp and Cp antigens was observed in group 1 and more Bb antigens was detected in group 2. The group 1 exhibited a positive correlation between the Bb and MVD percentage, between CD45 and Mp, and between MMP9 with Mp. These correlations were not observed in the group 2. Electron microscopy revealed the presence of structures compatible with microorganisms that feature Borrelia and Mycoplasma characteristics. Conclusions The presence of infectious agents, inflammatory cells and collagenases in mitral valves appear to contribute to the pathogenesis of MVD. Mycoplasma pneumoniae was strongly related with myxomatous mitral valve degeneration. Despite of low percentage of Borrelia burgdorferi in MD group, this agent was correlated with myxomatous degeneration and this may occour due synergistic actions between these infectious agents likely contribute to collagen degradation.