Avoiding Catastrophe: Understanding Free Light Chain Testing in the Evaluation of ATTR Amyloidosis

Recent advances in the diagnostic methods and therapeutic strategies of transthyretin cardiac amyloidosis

Cardiac amyloidosis is a progressive disease characterized by the buildup of amyloid fibrils in the extracellular space of the heart. It is divided in 2 main types, immunoglobulin light chain amyloidosis and transthyretin amyloidosis (ATTR), and ATTR amyloidosis is further divided in 2 subtypes, non-hereditary wild type ATTR and hereditary mutant variant amyloidosis. Incidence and prevalence of ATTR cardiac amyloidosis is increasing over the last years due to the improvements in diagnostic methods. Survival rates are improving due to the development of novel therapeutic strategies. Tafamidis is the only disease-modifying approved therapy in ATTR amyloidosis so far. However, the most recent advances in medical therapies have added more options with the potential to become part of the therapeutic armamentarium of the disease. Agents including acoramidis, eplontersen, vutrisiran, patisiran and anti-monoclonal antibody NI006 are being investigated on cardiac function in large, multicenter controlled trials which are expected to be completed within the next 2-3 years, providing promising results in patients with ATTR cardiac amyloidosis. However, further and ongoing research is required in order to improve diagnostic methods that could provide an early diagnosis, as well as survival and quality of life of these patients.

Advances in the diagnosis and treatment of transthyretin amyloid cardiomyopathy

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an underrecognized cause of heart failure (HF). ATTR-CM can lead to a number of cardiovascular manifestations including HF, rhythm disturbances, and valvular disease that ultimately limit quality of life and prognosis. Due to advances in diagnostic modalities and therapeutic options, the prevalence of ATTR-CM is rising. There are several classes of medications under active investigation, though most therapies are most efficacious if instituted early on in the disease course. As such, early clinical recognition and prompt diagnosis are crucial to improving disease related outcomes. In this review, we highlight clinical manifestations of ATTR-CM as well as contemporary diagnostic and treatment approaches to the disease.

Light-chain cardiac amyloidosis for the non-expert: pearls and pitfalls

Cardiac amyloidosis (CA) is an uncommon, progressive, and fatal disease; the two main forms that can affect the heart are transthyretin CA and light chain CA (AL-CA). AL-CA is a medical urgency for which a diagnostic delay can be catastrophic for patients' outcome. In this manuscript, we focus on the pearls and pitfalls that are relevant to achieve a correct diagnosis and to avoid diagnostic and therapeutical delays. Through the aid of three unfortunate clinical cases, some fundamental diagnostic aspects are addressed, including the following: first, a negative bone scintigraphy does not exclude CA, with patients with AL-CA frequently showing no or mild cardiac uptake, and its execution should not delay hematological tests; second, fat pad biopsy does not have a 100% sensitivity for AL amyloidosis and, if negative, further investigations should be performed, particularly if the pre-test probability is high. Third, Congo Red staining is not sufficient to reach a definitive diagnosis and amyloid fibrils typing with mass spectrometry, immunohistochemistry, or immunoelectron microscopy is crucial. To achieve a timely and correct diagnosis, all the necessary investigations must be performed, always considering the yield and diagnostic accuracy of each examination.

Amyloid Transthyretin Cardiomyopathy in Elderly Patients With Aortic Stenosis Undergoing Transcatheter Aortic Valve Implantation

Background The prevalence of calcific aortic stenosis and amyloid transthyretin cardiomyopathy (ATTR-CM) increase with age, and they often coexist. The objective was to determine the prevalence of ATTR-CM in patients with severe aortic stenosis and evaluate differences in presentations and outcomes of patients with concomitant ATTR-CM undergoing transcatheter aortic valve implantation. Methods and Results Prospective screening for ATTR-CM with Technetium99-3,3-diphosphono-1,2-propanodicarboxylic acid bone scintigraphy was performed in 315 patients referred with severe aortic stenosis between August 2019 and August 2021. Myocardial Technetium99-3,3-diphosphono-1,2-propanodicarboxylic acid tracer uptake was detected in 34 patients (10.8%), leading to a diagnosis of ATTR-CM in 30 patients (Perugini ≥2: 9.5%). Age (85.7±4.9 versus 82.8±4.5; P=0.001), male sex (82.4% versus 57.7%; P=0.005), and prior carpal tunnel surgery (17.6% versus 4.3%; P=0.007) were associated with coexisting ATTR-CM, as were ECG (discordant QRS voltage to left ventricular wall thickness [42% versus 12%; P<0.001]), echocardiographic (left ventricular ejection fraction 48.8±12.8 versus 58.4±10.8; P<0.001; left ventricular mass index, 144.4±45.8 versus 117.2±34.4g/m2; P<0.001), and hemodynamic parameters (mean aortic valve gradient, 23.4±12.6 versus 35.5±16.6; P<0.001; mean pulmonary artery pressure, 29.5±9.7 versus 25.8±9.5; P=0.037). Periprocedural (cardiovascular death: hazard ratio [HR], 0.71 [95% CI, 0.04-12.53]; stroke: HR, 0.46 [95% CI, 0.03-7.77]; pacemaker implantation: HR, 1.54 [95% CI, 0.69-3.43]) and 1-year clinical outcomes (cardiovascular death: HR, 1.04 [95% CI, 0.37-2.96]; stroke: HR, 0.34 [95% CI, 0.02-5.63]; pacemaker implantation: HR, 1.50 [95% CI, 0.67-3.34]) were similar between groups. Conclusions Coexisting ATTR-CM was observed in every 10th elderly patient with severe aortic stenosis referred for therapy. While patients with coexisting pathologies differ in clinical presentation and echocardiographic and hemodynamic parameters, peri-interventional risk and early clinical outcomes were comparable up to 1 year after transcatheter aortic valve implantation. REGISTRATION URL: https://www.clinicaltrials.gov. Unique identifier: NCT04061213.

Monoclonal Gammopathy of Undetermined Significance in Patients With Transthyretin Amyloidosis (ATTR): Analysis Using the iStopMM Criteria

INTRODUCTION

To identify the prevalence of monoclonal gammopathy of undetermined significance (MGUS) in patients with transthyretin amyloid (ATTR). We used the iStopMM study revised reference ranges for serum free light-chain (sFLC) corrected for eGFR to identify ATTR patients with light-chain MGUS (LC-MGUS). Characteristics and frequencies of the ATTR cohort with underlying MGUS was compared to a cohort of MGUS patients without ATTR.

PATIENTS AND METHODS

A retrospective analysis of ATTR and MGUS patients evaluated at our center between January 2014 to December 2021. A total of 149, predominantly male (87.5%) ATTR patients with a median age of 82 were included. This cohort was compared to 228 MGUS patients.

RESULTS

Of the 149 ATTR patients, 27 (18.1%) had coexisting MGUS. Among ATTR patients with MGUS, 12/27 (44%) had LC-MGUS based on sFLC abnormalities assessed using the iStopMM reference ranges. Of the MGUS only cohort, 44/228 (19.3%) met criteria for LC-MGUS. Utilizing the iStopMM reference ranges, 6 ATTR patients did not meet criteria for abnormal sFLCs, uncovering a 20% false-positive rate.

CONCLUSION

We noted higher rates of MGUS, particularly LC-MGUS, among ATTR patients when compared to our MGUS only cohort. The high prevalence remained after utilizing the iStopMM sFLC corrected for eGFR reference ranges. Additionally, 6 ATTR patients with renal-dysfunction would have met MGUS criteria if not evaluated using the iStopMM revised measures. These findings emphasize careful interpretation of sFLC abnormalities and encourage providers to keep ATTR on the differential when work-up uncovers sFLC aberrations.

Step‐by‐step typing for the accurate diagnosis of concurrent light chain and transthyretin cardiac amyloidosis

While ^99mTc‐pyrophosphate scintigraphy is clearly useful in diagnosing transthyretin amyloid cardiomyopathy (ATTR‐CM), it is necessary to know the pitfalls of this test for proper use. We present a rare case of concurrent ATTR‐CM and amyloid light chain (AL) cardiomyopathy. The patient showed congestive heart failure with left ventricular hypertrophy. ^99mTc‐pyrophosphate scintigraphy revealed abnormal cardiac uptake of Grade 3, a typical feature for ATTR‐CM. However, the patient showed renal impairment with proteinuria and the presence of monoclonal gammopathy, which rather suggested AL amyloidosis. Endomyocardial biopsy, immunohistochemistry, and proteomic analysis by laser microdissection with liquid chromatography‐coupled tandem mass spectrometry were performed, which finally confirmed both ATTR‐CM and AL cardiomyopathy. This case implicates the importance of combining examinations and precisely interpreting the results to diagnose cardiac amyloidosis accurately.