What is the likely underlying etiology of cardiomyopathy in a patient with diastolic dysfunction and a small, thickened left ventricle?

In this scenario, the description of the patient having diastolic dysfunction along with a small, thickened left ventricle is highly suggestive of hypertrophic cardiomyopathy, which is often associated with conditions such as amyloidosis. Amyloidosis leads to the deposition of amyloid protein in the cardiac tissue, causing both thickening of the ventricular walls and stiffness, thereby resulting in diastolic dysfunction.

This condition is characterized by the inability of the heart to relax properly, which is a hallmark of diastolic dysfunction. The small size of the thickened left ventricle further aligns with the features of restrictive cardiomyopathy caused by infiltrative processes like amyloidosis, rather than other forms of cardiomyopathy that would present with different ventricular dimensions or wall characteristics.

In contrast, chronic hypertension could lead to left ventricular hypertrophy, but it typically results in a larger left ventricle over time due to sustained pressure overload. Alcoholism and myocarditis can cause dilated cardiomyopathy or other heart changes, but are less likely to result in the specific combination of a small, thickened left ventricle and diastolic dysfunction that amyloidosis presents with. Therefore, amyloidosis is the most fitting etiology