In patients with suspected cardiac amyloidosis, the next diagnostic step is assessment of serum free light chains. Measurement of serum free light chains combined with serum and urine immunofixation electrophoresis has > 99% sensitivity for diagnosing AL type amyloidosis.
If the serum and urine tests are suggestive of AL cardiac amyloidosis, then an endomyocardial biopsy can be considered to confirm the diagnosis.
Endomyocardial biopsy is done to confirm the diagnosis of cardiac amyloidosis. Amyloid deposits are visible on hematoxylin and eosin–stained histologic sections as amorphous, eosinophilic deposits. Hematoxylin and eosin is not specific for amyloid and can stain hyaline changes similarly. Congo Red staining should therefore be used to confirm amyloid fibril deposition. Typing of the amyloid deposits by antibody-based methods or others should then be performed. Because amyloidosis is associated with bleeding diathesis and vascular fragility, endomyocardial biopsy could cause complications. In a large study of the safety of endomyocardial biopsy in cardiac amyloidosis, four complications occurred after 73 procedures, resulting in a complication rate of approximately 5.5%.
Cardiac MRI alone is not diagnostic of cardiac amyloidosis. Cardiac MRI is the appropriate test when an infiltrative cardiomyopathy is suspected but cardiac amyloidosis is less likely, such as sarcoidosis, hemochromatosis, Fabry disease, hypertrophic cardiomyopathy, myocarditis, or constrictive pericarditis.
Bone scintigraphy is diagnostic for ATTR cardiac amyloidosis if there is grade 2 or 3 cardiac uptake or a heart-to-contralateral ratio > 1.5 in the setting of normal light chain assays. False-positive results on bone scintigraphy may occur from AL cardiac amyloidosis. Thus, it is imperative to test light chains before proceeding with bone scintigraphy. If clinical suspicion for ATTR cardiac amyloidosis is high, then light chains should be obtained concomitantly with bone scintigraphy.
The results of this patient's light chain assays are as follows:
Kappa free light chain: 224 mg/dL (reference range, 0.3300-1.94 mg/dL)
Lambda free light chain: 0.7150 mg/dL (reference range, 0.5700-2.63 mg/dL)
Kappa/lambda free light chain ratio: 313 (reference range, 0.2600-1.25)
Total kappa chain: 12.5 mg/dL (reference range, < 0.9000 mg/dL)
Total lambda chain < 0.7000 mg/dL (reference range, < 0.7000 mg/dL)
Total kappa/lambda free light chain ratio > 17.9 (reference range, 0.7000-6.20)
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