When Light Chains Cause a Heavy Heart

Amyloidosis

Definition:

– Extracellular tissue deposition of fibrils composed of low molecular weight subunits of a variety of proteins

– Has a characteristic gross pathologic and microscopic appearance (ie apple-green birefringence with polarized light microscopy of Congo red stained tissue)

Broad Categorization: One useful approach to amyloidosis is to categorize the disease into 3 broad categories based on the type of protein secreted/deposited

1. AL Amyloidosis

– plasma cell dyscrasia of monoclonal light chain fragments

– usually multi-organ systemic disorder: nephrotic range proteinuria & edema, HSM, cardiac involvement +  neurologic, MSK, & hematologic manifestations

– can occur alone or in association with multiple myeloma (in other words not all patients with AL will meet overt diagnostic criteria for MM)

2. AA Amyloidosis

– fibrils are composed of acute phase reactant serum amyloid A

– complication of chronic diseases (eg RA, IBD, spondyloarthropathy)

– most commonly involves the kidney

– cardiac involvement can occur but is much less likely than with AL or senile amyloidosis

3. Age-Related (Systemic Senile Amyloidosis)

– transthyretin (TTR) protein

– may be secondary to either a wild-type OR hereditary/germline mutation

– much less significant renal involvement than the other 2 subgroups

– cardiac involvement is common (but better prognosis than AL cardiac involvement)

4. Don’t forget that there are other types of amyloidosis as well…

– eg dialysis related amyloidosis  (protein deposited is beta-2-microglobulin)

A few pearls on amyloid cardiomyopathy:

– Heart failure is the most common presentation

– Conduction system disease is much more common in TTR subtype

– Low voltage in the limb leads is one of the most common ECG abnormalities and is a great clue!

– The involved cardiac vessels are typically small and intramyocardial; as a result, coronary angiography is usually normal or shows only minor abnormalities — even if patients have angina or elevated cardiac biomarkers

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