325 Dealing with cardiac amyloidosis diagnosis: keep calm and use the magnifying glasses!

Methods and results Case report— male, 71 years old. Past medical history—arterial hypertension, dyslipidemia, tobacco abuse. COPD on nocturnal CPAP therapy. Rheumatic polymyalgia on steroid therapy. Previous unprovoked deep vein thrombosis on anticoagulation with rivaroxaban. Bilateral carpal tunnel surgeries 8 years ago. Spontaneous left biceps tendon rupture 4 year ago. IgA kappa monoclonal gammopathy of undetermined significance (MGUS). Mild interventricular septum (IVS) hypertrophy on echocardiography since 2018. In 2019 IVS was 18 mm with granular sparkling appearance. In February 2020 he was hospitalized for initial heart failure and COPD exacerbation. In 2021 he developed worsening dyspnoea. He underwent cardiological evaluation in a spoke hospital and a cardiac magnetic resonance (CMR) suggested infiltrative cardiomyopathy. Bone scintigraphy showed moderate cardiac uptake (Perugini Score 2). Following haematological evaluation, fat pad biopsy was performed, and amyloid was detected on Congo red staining. Classification of the amyloid fibril protein was not performed. Bone marrow biopsy, even though of suboptimal quality, was negative for amyloid and for plasma cellular infiltration. Bone marrow aspirate showed 11% of plasma cells and multiple myeloma was therefore hypothesized. Recent medical history—he was evaluated in our Cardiac Amyloid Outpatient Clinic in May 2021. He was symptomatic for dyspnoea (NYHA class III) and exercise intolerance, diffuse osteo-muscolar pain, and extremities paresthesia. His blood pressure was on the low side of normality with necessity of anti-hypertensive therapy downgrading. Signs and symptoms of hematological disease were not present. We required to analyse the fat pad specimen in order to perform amyloid fibril protein typing; with immunoelectron microscopy, transthyretin (TTR) was identified as the amyloid fibrils precursor (no light chains could be identified). We considered performing endomyocardial biopsy to exclude the coexistence of ATTR amyloidosis and light chains (AL) amyloidosis in the heart but, given the history, clinical picture, and fat pad biopsy results, we felt that cardiac ATTR was the most probable diagnosis and we decided to proceed with a close cardiological and haematological follow-up. TTR genetic testing is ongoing. Conclusions ATTR cardiac amyloidosis is an emerging cause of heart failure, especially with preserved ejection fraction, in the older population. However, these patients frequently present with dysproteinemias and bone marrow abnormalities, up to multiple myeloma, raising the issue of differential diagnosis between ATTR and AL amyloidosis. According to the latest European Consensus Document, in the presence of cardiac uptake at bone scintigraphy (Grades 1–3) and positive haematologic tests, histological confirmation (usually cardiac) is necessary to subtype amyloid infiltration. In our case, the patient had positive Congo Red-stained fat pad biopsy, but the typing of the amyloid deposition was not performed. After referral to a Center with a Cardiac Amyloid Outpatient Clinic with a specialized Pathology Unit, we could further proceed with diagnostic workup and identify the amyloid deposition as ATTR; of note, fat pad biopsy is positive in just 15–25% of ATTR amyloidosis. Moreover, close collaboration with Hematology was necessary to assess the risk of AL amyloidosis and to provide a close and targeted follow-up. Endomyocardial biopsy was not performed after consideration of the various elements suggestive for ATTR cardiac amyloidosis, but the patient will be evaluated periodically and closely to potentially reassess this decision.

A comparison of immunohistochemistry and mass spectrometry for determining the amyloid fibril protein from formalin-fixed biopsy tissue

Amyloidosis is caused by deposition in tissues of abnormal protein in a characteristic fibrillar form. There are many types of amyloidosis, classified according to the soluble protein precursor from which the amyloid fibrils are derived. Accurate identification of amyloid type is critical in every case since therapy for systemic amyloidosis is type specific. In ∼20–25% cases, however, immunohistochemistry (IHC) fails to prove the amyloid type and further tests are required. Laser microdissection and mass spectrometry (LDMS) is a powerful tool for identifying proteins from formalin-fixed paraffin-embedded tissues. We undertook a blinded comparison of IHC, performed at the UK National Amyloidosis Centre, and LDMS, performed at the Mayo Clinic, in 142 consecutive biopsy specimens from 38 different tissue types. There was 100% concordance between positive IHC and LDMS, and the latter increased diagnostic accuracy from 76% to 94%. LDMS in expert hands is a valuable tool for amyloid diagnosis.

Transthyretin and Amyloid in the Islets of Langerhans in Type-2 Diabetes

Transthyretin (TTR) is a major amyloid fibril protein in certain systemic forms of amyloidosis. It is a plasma protein, mainly synthesized by the liver but expression occurs also at certain minor locations, including the endocrine cells in the islets of Langerhans. With the use of immunohistochemistry and in situ hybridization, we have studied the distribution of transthyretin-containing cells in islets of Langerhans in type-2 diabetic and nondiabetic individuals. TTR expression was particularly seen in alpha (glucagon) cells. Islets from type-2 diabetic patients had proportionally more transthyretin-reactive islet cells, including beta cells. A weak transthyretin immunoreaction in IAPP-derived amyloid occurred in some specimens. In seeding experiments in vitro, we found that TTR fibrils did not seed IAPP while IAPP fibrils seeded TTR. It is suggested that islet expression of transthyretin may be altered in type-2 diabetes.