Extensive diagnostic workup of a patient suspected of having cardiac hereditary transthyretin amyloidosis (hATTR) finally revealed a beta 2-microglobulin-type amyloidosis, according to an article published in European Heart Journal – Case Reports.
In the article, researchers presented the case of a 63-year-old male patient referred to the clinic for possible cardiac hATTR testing.
The results of serum and urine immunofixation electrophoresis showed the absence of monoclonal bands, and the serum kappa/lambda light chain ratio was normal. These findings excluded a diagnosis of light chain amyloidosis.
The patient then underwent bone scintigraphy imaging that demonstrated diffuse radiotracer uptake in the myocardium, while genetic testing of the Transthyretin gene came back negative for variants. This workup indicated a diagnosis of wild-type cardiac hATTR.
Read more about hATTR testing
However, the patient also had a endomyocardial biopsy due to the young age of presentation and his strong family history of cardiac hATTR despite no variants in the Transthyretin gene.
This workup helped establish a diagnosis of beta 2-microglobulin-type amyloidosis, and genetic testing of the beta 2-microglobulin gene showed a heterozygous Pro32Leu (p. P52L) mutation. He underwent heart transplantation and sustained normal graft function 2 years postsurgery.
“Despite the high sensitivity and specificity of bone scintigraphy in the diagnosis of ATTR amyloidosis, clinicians should be aware of the rarer forms that may be suggested by an earlier age at presentation and/or a suspicious family history,” Haslett and colleagues explained.
“With these clinical clues, an endomyocardial biopsy may uncover a rarer form for which tafamidis is not indicated, family screening may be required, and prognosis may vary.”
Cardiac amyloidosis is caused by the deposition of misfolded proteins in the myocardium, most often the transthyretin or light chain proteins. However, several other, rare forms of cardiac amyloidosis may present as false-positive bone scintigraphy imaging results and can only be revealed by endomyocardial biopsy.
Haslett JJ, Patel JK, Kittleson MM. Beta 2-microglobulin: case report of a rare cause of cardiac amyloidosis. Eur Heart J Case Rep. Published online May 8, 2023. doi:10.1093/ehjcr/ytad239