Cardiac amyloidosis in hereditary neuropathic amyloidosis diagnosed by endomyocardial biopsy.

A 57 year old male first developed progressive neuropathy of the lower extremities and then similar involvement in the upper extremities. Two years later he developed dyspnea and then complete atrioventricular block requiring the use of a permanent cardiac pacemaker. An older brother had an almost identical clinical course, including the installation of a permanent pacemaker. Both died of left ventricular failure. An endomyocardial biopsy revealed extensive amyloidosis and fibrosis of the myocardium. This is the first report of a myocardial biopsy showing amyloid on electron microscopy.