[Unclassified cardiomyopathies: subspecies and their transformation].

Some cases with hypertrophic cardiomyopathy (HCM) progress to dilated cardiomyopathy (DCM), therefore, we hypothesized that a transforming-type phase between HCM and DCM could exist. This study was made based on a retrospective analysis of 471 of 1,388 patients with cardiomyopathy who underwent diagnostic myocardial biopsy in several hospitals between 1977 to 1995, and who were not diagnosed with restrictive cardiomyopathy, arrhythmogenic right ventricular dysplasia, specific heart muscle diseases, or electrical disturbance type of heart muscle diseases. Based on echocardiographic measurements, the 471 patients were classified into eight subgroups according to the presence or absence of three parameters. A: left ventricular hypertrophy (septal or posterior wall thickness > 12 mm), B: left ventricular dilation (left ventricular end-diastolic dimension > 55 mm), C: systolic dysfunction (left ventricular ejection fraction < 50%), is signified by plus or minus ([ABC]). HCM, DCM and normal heart are defined as [+(-)-], [-(+2)] and [-(-)-], respectively. Unclassified cardiomyopathy (UCM) was indicated as cardiomyopathy not diagnosed as HCM or DCM. Therefore, unclassified cardiomyopathies are signified as either [+2-], [+(-)+], [+3], [-(+)-] or [-(-)+]. Patients in each subgroup of UCM were followed up for 6.4 +/- 6.0 years and their clinical courses compared with the histological findings. Of the 471 patients, 111 (24%) were classified as UCM, 240 as HCM, and 120 as DCM. Severe myocardial disarray was noted more frequently in UCM [17 of 111 cases (15%)] than in DCM [7 of 120 cases (6%)] (p < 0.05), and not significantly higher than in HCM [34 of 240 cases (14%)]. Patients with UCM whose conditions deteriorated had positive pathological findings (15 of 26 cases) more often than those without deterioration (8 of 29 cases; p < 0.05). UCM could be a transforming type of cardiomyopathy for some patients with HCM who progress to DCM. In addition, there may be a positive correlation between the histopathologic findings and the clinical course.