We have read with interest the Image in cardiology report by García-González et al.,1 which shows intense uptake of the amyloid tracer 18F-florbetapir on PET/CT (positron emission tomography/computed tomography) in a 75-year-old man with multiple myeloma and heart failure. In the accompanying text, the authors link the positivity of this test with the histological diagnosis of cardiac amyloidosis (CA) and indicate that this test can avoid the risk of cardiac biopsy-related complications.
Without completely dismissing the usefulness of this new imaging test, we believe it important to review some of the fundamental concepts in the clinical treatment of patients with CA:
- 1.
A diagnosis of CA requires histological evidence of amyloid deposits, either in the heart itself or in biopsies from other affected organs.2 If the biopsy is obtained from an organ other than the heart, the typical signs of CA need to be seen in cardiac imaging tests (echocardiography). False positives are possible in any imaging test, and CA diagnosis frequently has serious prognostic and therapeutic implications.
- 2.
A generic diagnosis of CA is insufficient. The substance deposited needs to be identified because prognosis and treatment vary considerably according to the type of CA.3 This requires immunohistochemical characterization of the amyloid material found in the biopsy, as well as demonstration of circulating amyloid protein in serum (amyloid light-chain amyloidosis [AL]) or a causative genetic mutation (transthyretin familial amyloidosis).
Physicians can only recommend radical therapeutic options such as transplantation or chemotherapy after identification of the specific type of amyloidosis.3 The patient studied by García-González et al.1 does indeed have a high probability of having myeloma-associated AL amyloidosis but, due to his age and sex, might actually have senile CA (due to deposition of wild-type transthyretin), which would involve a different prognosis and therapeutic approach.4 Only when senile CA is suspected (due to its more benign behavior and the absence of a specific treatment) is it suggested that 99mtechnetium scintigraphy could obviate the need for endomyocardial biopsy.5 Nonetheless, the appropriate course of action remains unclear.
In conclusion, we believe that the emergence of 18F-florbetapir PET/CT for the diagnosis of CA is excellent news, especially if it is shown to be more sensitive than the other imaging techniques currently used for this purpose (ultrasound and magnetic resonance),6 but biopsy of the affected organ is still required. In general, “blind” biopsies of unaffected tissues (such as abdominal fat and oral or anal mucosa) have less value and can delay diagnosis to a dangerous degree.7 Only rapid identification of the different subtypes of CA and their specific treatment will improve the bleak prognosis of these patients.