CARDIAC AMYLOIDOSIS IN ELDERLY WITH POSITIVE SCINTIGRAPHY AND MONOCLONALITY: A DIAGNOSTIC DILEMMA

Abstract

Abstract Background and Aims Clinical identification of elderly patients with both wild–type transthyretin amyloidosis (ATTR) and monoclonal gammopathy of unknown significance (MGUS) is increasing. For this reason, accurate amyloid histologic subtyping is crucial in case of concomitant positivity of bisphosphonate scintigraphy and monoclonal protein testing. We report the diagnostic work–up of cardiac amyloidosis in this specific patient subtype in our tertiary referral center. Methods Among 133 patients who received the diagnosis of cardiac amyloidosis from March 2021 to March 2023, 21 (16%) presented with an abnormality of both bisphosphonate scintigraphy and at least one of the serum monoclonal protein tests. Patients underwent abdominal fat biopsy/needle aspiration as the first diagnostic procedure. In case of negative results, an endomyocardial biopsy (EMB) was planned. Amyloid was identified at histology by Congo Red staining. Amyloid typing was obtained by immunohistochemistry using a recently developed amyloid antibody panel AmYkit (Amimed) applicable on fixed paraffin–embedded tissues in an automated platform. The results were compared with those obtained with standard immunohistochemistry. Results Sixteen of the 21 patients were older than 75 years (76%, 81±10 ys) with a grade 3 (62%) or 2 (33%) scintigraphy. A grade 1 positive scintigraphy was detected in one patient. Serum immunofixation revealed a previously unknown monoclonal protein peak in 78%, while 22% had a history of MGUS. None of the patients had hematologic disorders. TTR pathogenic mutation was detected in one patient. On pathologic examination, abdominal fat was negative for amyloid in all cases, while Congo Red staining was positive in all examined EMBs. Immunohistochemistry performed with standard antibodies was not able to discriminate between AL and ATTR, due to signal overlapping of variable intensity. Conversely, our preliminary results with AmYkit panel of antibodies demonstrate absence of signal overlapping in over 90% of cases, allowing accurate histologic discrimination between AL and TTR. Conclusion Based on our clinical and histologic observations, in elderly patients with concomitant positivity of both bisphosphonate scintigraphy and monoclonal protein testing, TTR is the most frequent type of cardiac amyloid. EMB is a useful diagnostic tool to confirm the clinical suspicion of amyloidosis. Accurate amyloid subtyping is granted by a more sensitive panel of antibodies.