Myxomatous degeneration of valves also occurs with Marfan's syndrome and other inherited connective tissue abnormalities. Rheumatic heart disease is a frequent cause of aortic regurgitation and is the most common cause of multivalvular heart disease. Isolated outbreaks of rheumatic fever continue to be reported in the United States, even in relatively affluent communities. Rheumatic heart disease remains a significant problem in immigrants, especially those from Latin America and Southeast Asia. Rheumatic fever appears to cause valvular heart disease by an autoimmune phenomenon whereby antibodies against streptococcal antigens cross-react with valvular tissue.
Valvular involvement can present acutely as a result of edema of valvular tissue.
Progressive fibrosis, superimposed calcification, and scarring with retraction of leaflet tissue lead to valvular stenosis, incompetence, or both. The interval between the occurrence of rheumatic fever and clinical manifestations varies, as does the degree of involvement. Both mitral and aortic valves are usually involved. Factors found to promote degenerative valvular changes are increasing age, a low body mass index, and hypertension. Histologic changes that simulate atheroma and involve lipid deposition and inflammatory cell infiltration of the leaflets have been described in patients with early degenerative changes in the aortic leaflets.