Myxomatous degeneration is a pathological weakening of connective tissue. Since it occurs in conjunction with an accumulation of dermatan sulfate, a glycosaminoglycan, within the connective tissue matrix of the mitral valve, myxomatous degeneration is the most common cause of pure mitral valve insufficiency. In myxomatous degeneration, the structural protein collagen forms abnormally and causes thickening, enlargement, and redundancy of the valve leaflets and chordae. In many cases, the degeneration is limited to the mitral valve and follows a benign course. When associated with systemic diseases, like Marfan syndrome, the degeneration is more extensive and involves other heart valves.
According to a British Heart Journal, excised valves of 499 patients were examined for pathological evidence of myxomatous degeneration. Thirty-six valves (7%) had myxomatous degeneration as a major pathological finding. Fourteen valves (3%) had significant myxomatous degeneration of the pars fibrosa, a finding which we define as "primary myxomatous degeneration". Echocardiographic findings and catheterization results were correlated with the clinical course, surgical results, and follow-up in these 14 patients. Echocardiograms in 10 of the 11 patients who had them (91%) showed abnormalities suggesting the presence of primary myxomatous degeneration. Echocardiography was more helpful than angiography in diagnosis.