Myocardium with myocyte dropout due to interstitial fibrosis and amyloid deposition, seen as lightly eosinophilic material within the bluish fibrous tissue.
A Congo red stain highlights the intermixed amyloid (pink material) associated with the myocytes.
In another area of the myocardium, amyloid deposit within a vessel can be appreciated. Note the amyloid vessel highlighted by the Congo Red stain on the right.
The heart is the major organ involved by senile systemic amyloidosis. The amyloid deposits can lead to a restrictive cardiomyopathy (diastolic dysfunction due to stiffening of ventricles) and arrhythmias. The amyloid protein is composed of transthyretin (TTR), which normally functions to transport thyroxine and retinol. Note that in sporadic senile amyloidosis, the TTR is structurally normal. However, mutant forms of TTR may also be deposited and interestingly, 4% of the US African-American population carry this mutant allele and cardiac amyloidosis has been identified in both homozygous and heterozygous patients.1
Aside from senile systemic amyloidosis, cardiac amyloidosis can occur in any form of systemic amyloidosis -- this includes primary amyloidosis associated with plasma cell dyscrasia or secondary amyloidosis associated with a reactive inflammatory process such as infections or rheumatoid arthritis. Many familial (inherited) forms of amyloidosis exist as well.
Histologically, deposits initially accumulate between the muscle fibers in the subendocardium and myocardium. Expansion of these amyloids eventually compress adjacent muscle fibers and lead to pressure necrosis. If the deposits involve the conduction system, arrhythmias may occur.
Primary amyloidosis, also called AL type for amyloid light chain elaborated by plasma cells, carries a poor prognosis. Management is directed at alleviating symptoms of heart failure (usually restrictive cardiomyopathy) and chemotherapy for the underlying plasma cell dyscrasia.2
Secondary amyloidosis, also called AA type for amyloid-associated proteins made by the liver, usually does not involve the heart -- in cases of cardiac involvement, clinical symptoms are usually mild.
In advances cases of senile systemic amyloidosis (deposition of wild type TTR) and familial amyloid neuropathies (inheritance of mutant TTR), cardiac transplanation may be considered.
1 Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis of Disease. 7th Ed. Philadelphia, PA: Elsevier; 2005: 258-64.
2 Mills SE, ed. Sternberg's Diagnostic Surgical Pathology. 5th ed. Philadelphia, PA: Lippincoott Williams & Wilkins; 2009: 1187-8.