Why does myxomatous disease of mitral valve occur
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myxomatous mitral valve disease pathogenesis degenerative mitral valve prolapse
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myxomatous mitral valve degeneration pathogenesis
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Myxomatous disease of the mitral valve occurs because the valve’s connective-tissue scaffold progressively weakens and remodels.
- The normal tough fibrosa layer, rich in collagen, becomes thinned and disorganized.
- The softer spongiosa layer expands with excess proteoglycans and glycosaminoglycans, often called myxoid or mucoid material.
- Collagen and elastin degradation, together with activation of valve interstitial cells and matrix metalloproteinases, produces enlarged, thick, floppy leaflets and elongated chordae.
- The leaflets then billow into the left atrium during systole, causing mitral valve prolapse; stretched chordae can rupture and lead to mitral regurgitation.
In most people it is primary degenerative disease, meaning the exact initiating cause is not known. It can be sporadic or familial and appears to have a polygenic, mechanically influenced basis. Defects in connective-tissue and extracellular-matrix biology, including altered TGF-beta signaling, are implicated, as summarized in this pathogenesis review.
It can also occur as part of inherited connective-tissue disorders, especially Marfan syndrome, and less commonly Ehlers-Danlos syndrome. Secondary prolapse may occur when another process distorts the valve apparatus or causes significant regurgitation.
Pathologically, the key changes are thinning of the fibrosa plus expansion of the spongiosa by myxomatous material, with elongation or rupture of chordae. Robbins & Kumar Basic Pathology, p. 329.
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