The causative mechanisms of mitral valve prolapse in progressive muscular dystrophy in reference to thorax and thoracic spine deformities and left ventricular dysfunction.

The causative mechanisms of mitral valve prolapse (MVP) were evaluated in 58 patients with progressive muscular dystrophy (PMD). Two possible causes, 1) left ventricular (LV) dysfunction and 2) thoracic spine and thorax deformities were assessed. Patients were classified into three groups by echocardiographic findings. Group 1: 31 patients without MVP, group 2: 11 patients with MVP confirmed only by M-mode echocardiogram, group 3: 16 patients with MVP confirmed by both two-dimensional and M-mode echocardiograms. LV functions evaluated by systolic time intervals and fractional shortening showed no significant differences among the three groups. Scoliosis of the thoracic spine was not related to the incidence of MVP. Lordotic or straight spines were found in 32.3%, 100%, 93.8% of cases in group 1, group 2 and group 3, respectively, and the incidences of MVP in cases with kyphosis, straight spine and lordosis were 4.8%, 66.7% and 77.8%, respectively. The shape of the thorax as evaluated by the ratio of anteroposterior internal diameter to transverse diameter was more flattened in groups 2 and 3 than in group 1. From these results, we concluded that LV dysfunction was not related to the incidence of MVP and that the lordotic or straight spine and the flattened thorax were supposed to be the major factors in the occurrence of MVP in PMD.