A 65-year-old female with congestive heart failure and chronic renal failure presents with shortness of breath and generalized body swelling. She reports her symptoms have worsened since yesterday. On physical exam, there is distention of the jugular venous pulse (JVP), presence of S3 on cardiac auscultation, and the presence of crackles bilaterally on lung auscultation. There is pitting edema of both lower legs. There are waxy papules in the axilla and inguinal region. Laboratory analysis reveals serum creatinine of 6.1 mg/dL, total protein level of 9.2 g/dL, and blood urea nitrogen (BUN) level of 85 mg/dL. Urine analysis reveals 3+ protein but with the absence of cells or cellular casts. An echocardiogram shows a thickened left ventricle with preserved systolic function. Which of the following is the most appropriate next step in the management of this patient?
Fat pad biopsy
Right heart catheterization
Bone marrow biopsy
Answer : A Fat pad biopsy
The waxy papules and cardiac findings make the diagnosis likely to be amyloidosis.
The subcutaneous abdominal fat aspirate is an easy and innocuous procedure that will stain Congo red positive with apple-green birefringence and has an 81% diagnostic sensitivity in AL amyloidosis. Fat pad biopsy is 60 to 80 percent sensitive for amyloidosis
The clinical features of amyloidosis vary depending on which type of amyloid fibrils are responsible.
Systemic amyloidosis can lead to heart failure with left ventricular hypertrophy on echocardiogram with standard or low voltage
Bone marrow biopsy would evaluate for plasma cells and anemia while being 50 to 60 percent sensitive for amyloidosis.