Cardiac amyloidosis (“stiff heart syndrome”) occurs when amyloid deposits infiltrate the normal heart muscle, and is a cause of what is called a restrictive cardiomyopathy. However, a number of tests are not consistent with that diagnosis at this point (unless this is very early in the disease process). Severe left atrial enlargement can occur in association with hypertension, aortic stenosis, mitral incompetence, mitral stenosis and hypertrophic cardiomyopathy:
Cardiac ECHO of a patient with Amyloid disease, showing a severe restrictive cardiomyopathy. LA, RA normal sizel LV, RV walls severely thickned.
An Echocardiogram of severe left atrial enlargement and mitral stenosis: