Utility and limitations of 3,3-diphosphono-1,2-propanodicarboxylic acid scintigraphy in systemic amyloidosis

Cardiac Amyloidosis: Updates in Imaging

PURPOSE OF REVIEW

We summarize key features pertaining to the two most commonly encountered types of cardiac amyloidosis (CA), monoclonal immunoglobulin light chain (AL) and transthyretin type (ATTR), expanding upon the clinical application and utility of various imaging techniques in diagnosing CA.

RECENT FINDINGS

Advances in imaging have led to earlier identification, improved diagnosis of CA and higher discriminatory power to differentiate CA from other hypertrophic phenocopies. The application of cardiac magnetic resonance imaging (CMR) has led to a deeper understanding of underlying pathophysiological processes in CA, owing largely to its intrinsic tissue characterization properties. The widespread adoption of bone scintigraphy algorithms has reduced the need for cardiac biopsy and improved diagnostic confidence in ATTR CA. As new treatments for CA are rapidly developing, there will be even greater reliance on imaging, as the requirement to diagnose disease earlier, monitor response and amend treatment strategies accordingly intensifies.

Systemic ATTR-amyloidosis, a Rare Form of Internal Organ Damage

The article presents the case report of a rare hereditary form of systemic ATTR-amyloidosis in Russian patient with a discussion of approaches to the diagnosis and treatment of this form, also based on the own experience in the management of such patients. Modern ideas about the pathogenesis of the disease as well as detailed information about the clinical manifestations of amyloid cardiopathy and of other organs are presented. The nature of structural and hemodynamic changes in the heart is discussed on the basis of experience, including own, ultrasound examination of the heart in patients with amyloidosis, especially the article focuses the reader's attention on the true infiltrative nature of transtiretin amyloid cardiopathy in contrast to AL-amyloidosis, in which there is a significant inflammatory component that determines a more unfavorable natural course of AL-amyloidosis of the heart. The article discusses the differential diagnosis of different types of amyloidosis, the diagnostic difficulties associated with weak congophilia of transtiretin amyloidosis and at the same time substantiates the need for morphological verification of the diagnosis. Modern methods of treatment of ATTR-amyloidosis are discussed.

Combination of Commonly Examined Parameters Is a Useful Predictor of Positive 99 mTc-Labeled Pyrophosphate Scintigraphy Findings in Elderly Patients With Suspected Transthyretin Cardiac Amyloidosis

BACKGROUND

A recent study revealed a high prevalence of transthyretin (TTR) cardiac amyloidosis (CA) in elderly patients. ^{99 m}Tc-labeled pyrophosphate (^{99 m}Tc-PYP) scintigraphy is a remarkably sensitive and specific modality for TTR-CA, but is only available in specialist centres; thus, it is important to raise the pretest probability. The aim of this study was to evaluate the characteristics of patients with ^{99 m}Tc-PYP positivity and make recommendations about patient selection for ^{99 m}Tc-PYP scintigraphy.Methods and Results:We examined 181 consecutive patients aged ≥70 years who underwent ^{99 m}Tc-PYP scintigraphy at Kumamoto University Hospital between January 2012 and December 2018. Logistic regression analyses showed that high-sensitivity cardiac troponin T (hs-cTnT) ≥0.0308 ng/mL, left ventricular posterior wall thickness ≥13.6 mm, and wide QRS (QRS ≥120 ms) were strongly associated with ^{99 m}Tc-PYP positivity. We developed a new index for predicting ^{99 m}Tc-PYP positivity by adding 1 point for each of the 3 factors. The ^{99 m}Tc-PYP positive rate increased by a factor of 4.57 for each 1-point increase (P<0.001). Zero points corresponded to a negative predictive value of 87% and 3 points corresponded to a positive predictive value of 96% for ^{99 m}Tc-PYP positivity.

CONCLUSIONS

The combination of biochemical (hs-cTnT), physiological (wide QRS), and structural (left ventricular posterior wall thickness) findings can raise the pretest probability for ^{99 m}Tc-PYP scintigraphy. It can assist clinicians in determining management strategies for elderly patients with suspected CA.

Accuracy of 99mTc-Hydroxymethylene diphosphonate scintigraphy for diagnosis of transthyretin cardiac amyloidosis

BACKGROUND AND AIM

Either 99mTechnetium diphosphonate (Tc-DPD) or pyrophosphate (Tc-PYP) scintigraphy plays a relevant role in diagnosing transthyretin cardiac amyloidosis (CA), and labeled radiotracers have been extensively studied in diagnosing CA. Few studies have analyzed and validated 99mTc-Hydroxymethylene diphosphonate (Tc-HMDP). Our aim was to validate the diagnostic accuracy of Tc-HMDP total-body scintigraphy in a cohort of patients with biopsy-proven transthyretin CA.

METHODS AND RESULTS

We retrospectively evaluated all patients undergoing 99mTc-HMDP total-body scintigraphy, in adjunct to a comprehensive diagnostic work-up for suspected CA. Sixty-five patients were finally diagnosed with CA, while it was excluded in 20 subjects with left ventricular hypertrophy of various etiologies. Twenty-six patients had AL-CA, 39 had TTR CA (16 TTRm, 23 TTRwt). At Tc-HMDP scintigraphy, 2 AL patients showed a Perugini score grade 1 heart uptake, while 24 showed no uptake. All TTR patients showed Tc-HMDP uptake, with three patients showing a Perugini score grade 1, 16 grade 2, and 20 grade 3, respectively. No uptake was observed in patients with left ventricular hypertrophy. A positive Tc-HMDP scintigraphy showed a 100% sensitivity and a 96% specificity for TTR CA identification.

CONCLUSIONS

Tc-HMDP scintigraphy is as accurate as Tc-DPD or Tc-PYP, and may therefore de facto be considered a valuable tool for the diagnosis of TTR CA.

Cardiac amyloidosis: A case report and review of literature

BACKGROUND

Cardiac amyloidosis, a disease caused by the precipitation of amyloid proteins in the myocardial extracellular matrix has been historically difficult to diagnose due to lack of specific clinical manifestations and necessity of biopsy to demonstrate amyloid deposition. However, advances in cardiovascular imaging techniques have facilitated earlier recognition of this disease. In addition, while once thought of as incurable, treatment strategies are emerging for cardiac amyloidosis, making early diagnosis essential.

CASE SUMMARY

We outline the case of a 73 years old African American female who was admitted with sudden onset shortness of breath and found to be in cardiogenic shock. Cardiac amyloidosis was suspected due to discordance between electrocardiogram and echocardiogram findings and this was subsequently confirmed with the aid of scintigraphy and an endomyocardial biopsy.

CONCLUSION

Our objective is to highlight the diagnostic evaluation and clinical implications of cardiac amyloidosis.

State-of-the-art radionuclide imaging in cardiac transthyretin amyloidosis

Cardiac amyloidosis, once considered untreatable, is now gaining well-deserved attention due to advances in imaging and the recent approval of targeted breakthrough therapies. In this paper, we discuss the role of radionuclide imaging in the evaluation and management of patients with the most common form of amyloidosis-cardiac transthyretin amyloidosis (ATTR). We provide a comprehensive summary of the literature interspersed with our institutional experience as appropriate, to deliver our perspective.

Bone scintigraphy imaging of cardiac amyloidosis

Transthyretin-related cardiac amyloidosis (ATTR) amyloidosis is an aggressive, rapidly progressive, and fatal disease, for which several promising therapies are in development. This condition is frequently underdiagnosed because of the limited specificity of echocardiography and the traditional requirement for histological diagnosis. It is well known that ^99mtechnetium-labeled bone scan radiotracers can localize in the myocardial amyloid deposits, but the use of this imaging modality to differentiate between the two subtypes has only lately been revisited. We report a case of a 76-year-old man with a clinical diagnosis of amyloidosis who underwent a bone scan that had features of ATTR amyloidosis. To the best of our knowledge, this is the first case report in Sub-Saharan Africa.

Analysis of the TTR gene in the investigation of amyloidosis: A 25-year single UK center experience

Transthyretin amyloidosis (ATTR) is caused by deposition of either wild-type (ATTRwt) or variant (ATTRm) transthyretin. ATTRwt presents with restrictive cardiomyopathy, while ATTRm displays a range of organ involvement. This retrospective analysis includes all patients referred to a single UK center in the last 25 years for clinical and laboratory assessment of known or suspected amyloidosis who underwent TTR gene sequencing. A total of 4459 patients were included in this study; 37% had final diagnosis of ATTR amyloidosis; 27% light chain amyloidosis; 0.7% other types of amyloidosis; 21.3% had no amyloid and 14% had no data. TTR variants were found in 770 (17%) cases; the most prevalent were p.V142I, p.T80A, and p.V50M identified in 42, 25, and 16%, respectively. The median age at referral in each group was: 76 (range 47-93), 66 (40-81), and 45 years (21-86), respectively. Overall 42 rare or novel variants were identified. Forty-two percent patients with ATTRm died at a median age of 73 years (33-89) with a median survival from diagnosis of 50 months. ATTRwt was the final diagnosis in 20% of patients undergoing genetic testing. Our findings of TTR variants in 17% of screened patients highlight the need for routine genetic testing in the evaluation of suspected ATTR amyloidosis.

Quantitation of 99mTc-DPD uptake in patients with transthyretin-related cardiac amyloidosis

PURPOSE

Transthyretin (ATTR) amyloidosis is a rare but serious infiltrative disease associated with a wide spectrum of morphologic and functional cardiac involvement. ^99mTc-labelled 3,3-diphosphono-1,2-propanodicarboxylic acid (DPD), initially developed as a bone-seeking radiotracer, is remarkably sensitive for imaging cardiac ATTR amyloid deposits. Our aim was to investigate the feasibility and utility of estimating ^99mTc-DPD uptake in myocardial tissue; this has the potential to yield reliable quantitative information on cardiac amyloid burden, which is urgently required to monitor disease progression and response to novel treatments.

METHODS

Three methods of quantitation were developed and tested on 74 patients with proven cardiac ATTR amyloidosis who had recently undergone ^99mTc-DPD planar whole-body imaging and SPECT-CT. Quantitative results were compared to measurements of extracellular volume fraction (ECV) by cardiac magnetic resonance imaging, a validated technique for measuring amyloid burden.

RESULTS

An experienced clinician graded uptake using a widely-used visual scoring system as 1 (n = 15), 2 (n = 39) or 3 (n = 20). Linear correlations between the SPECT and ECV data (p < .001) were demonstrated. None of the methods showed that ^99mTc-DPD uptake in the heart was significantly greater in patients with grade-3 uptake than in those with grade-2 uptake.

CONCLUSIONS

Quantitation of ^99mTc-DPD uptake in cardiac transthyretin amyloid deposits is complex and is hindered by competition for radiotracer with amyloid in skeletal muscle. The latter underlies differences in uptake between grade-2 and grade-3 patients, not cardiac uptake.

Technetium pyrophosphate uptake in transthyretin cardiac amyloidosis: Associations with echocardiographic disease severity and outcomes

BACKGROUND

Quantitative uptake of Technetium 99 m-pyrophosphate (TcPYP) is sensitive and specific for diagnosing transthyretin cardiac amyloidosis (ATTR). We sought to examine the association between TcPYP uptake intensity and echocardiographic measures of disease severity and clinical outcomes.

METHODS AND RESULTS

A retrospective analysis was performed of 75 patients who underwent TcPYP scintigraphy. Planar images were evaluated semiquantitatively and using heart-to-contralateral lung (H/CL) ratio. The associations between H/CL ratio and echocardiographic parameters and outcomes were evaluated using linear regression and Cox models, respectively. There were 48 patients diagnosed with ATTR with mean H/CL ratio 1.58 ± 0.22 (vs 1.08 ± 0.09 if semiquantitative score = 0). The H/CL ratio was not associated with any measured echocardiographic parameter. Both semiquantitative uptake grade and H/CL ratio were associated with all-cause mortality (P = 0.009 and 0.007, respectively) and all-cause mortality or heart failure hospitalization (P = 0.001 and 0.020, respectively); however, neither were associated with outcomes when limited to patients with confirmed ATTR (P = 0.18 and 0.465, respectively).

CONCLUSION

In patients with suspected ATTR, quantitative and semiquantitative uptake intensity of TcPYP is associated with all-cause mortality as well as all-cause mortality or heart failure hospitalization. However, in those with confirmed ATTR, there is no association with echocardiographic disease severity or outcomes.

Prognostic utility of the Perugini grading of 99mTc-DPD scintigraphy in transthyretin (ATTR) amyloidosis and its relationship with skeletal muscle and soft tissue amyloid

Aims

High-grade (Perugini grade 2 or 3) cardiac uptake on bone scintigraphy with 99mTechnetium labelled 3,3-diphosphono-1,2-propanodicarboxylic acid (99mTc-DPD) has lately been confirmed to have high diagnostic sensitivity and specificity for cardiac transthyretin (ATTR) amyloidosis. We sought to determine whether patient stratification by Perugini grade on 99mTc-DPD scintigraphy has prognostic significance in ATTR amyloidosis.

Methods and results

Patient survival from time of 99mTc-DPD scintigraphy was determined in 602 patients with ATTR amyloidosis, including 377 with wild-type ATTR (ATTRwt) and 225 with mutant ATTR (ATTRm) amyloidosis. Patients were stratified according to Perugini grade (0-3) on 99mTc-DPD scan. The prognostic significance of additional patient and disease-related factors at baseline were determined. In the whole cohort, the finding of a Perugini grade 0 99mTc-DPD scan (n = 28) was invariably associated with absence of cardiac amyloid according to consensus criteria as well as significantly better patient survival compared to a Perugini grade 1 (n = 28), 2 (n = 436) or 3 (n = 110) 99mTc-DPD scan (P < 0.005). There were no differences in survival between patients with a grade 1, grade 2 or grade 3 99mTc-DPD scan in ATTRwt (n = 369), V122I-associated ATTRm (n = 92) or T60A-associated ATTRm (n = 59) amyloidosis. Cardiac amyloid burden, determined by equilibrium contrast cardiac magnetic resonance imaging, was similar between patients with Perugini grade 2 and Perugini grade 3 99mTc-DPD scans but skeletal muscle/soft tissue to femur ratio was substantially higher in the latter group (P < 0.001).

Conclusion

99mTc-DPD scintigraphy is exquisitely sensitive for identification of cardiac ATTR amyloid, but stratification by Perugini grade of positivity at diagnosis has no prognostic significance.

Multimodality Imaging in Restrictive Cardiomyopathies: An EACVI expert consensus document In collaboration with the "Working Group on myocardial and pericardial diseases" of the European Society of Cardiology Endorsed by The Indian Academy of Echocardiography

Restrictive cardiomyopathies (RCMs) are a diverse group of myocardial diseases with a wide range of aetiologies, including familial, genetic and acquired diseases and ranging from very rare to relatively frequent cardiac disorders. In all these diseases, imaging techniques play a central role. Advanced imaging techniques provide important novel data on the diagnostic and prognostic assessment of RCMs. This EACVI consensus document provides comprehensive information for the appropriateness of all non-invasive imaging techniques for the diagnosis, prognostic evaluation, and management of patients with RCM.

Clinical characteristics of wild-type transthyretin cardiac amyloidosis: disproving myths

Aims

Wild-type transthyretin amyloidosis (ATTRwt) is mostly considered a disease predominantly of elderly male, characterized by concentric LV hypertrophy, preserved LVEF, and low QRS voltages. We sought to describe the characteristics of a large cohort of ATTRwt patients to better define the disease.

Methods and results

Clinical findings of consecutive ATTRwt patients diagnosed at 2 centres were reviewed. ATTRwt was diagnosed histologically or non-invasively (LV hypertrophy ≥12 mm, intense cardiac uptake at 99mTc-DPD scintigraphy and AL exclusion). Mutations in TTR were excluded in all cases. The study cohort comprised 108 patients (78.6 ± 8 years); 67 (62%) diagnosed invasively and 41 (38%) non-invasively. Twenty patients (19%) were females. An asymmetric hypertrophy pattern was observed in 25 (23%) patients. Mean LVEF was 52 ± 14%, with 39 patients (37%) showing a LVEF < 50%. Atrial fibrillation (56%) and a pseudo-infarct pattern (63%) were the commonest ECG findings. Only 22 patients fulfilled QRS low-voltage criteria while 10 showed LV hypertrophy on ECG. Although heart failure was the most frequent profile leading to diagnosis (68%), 7% of individuals presented with atrioventricular block and 11% were diagnosed incidentally. Almost one third (35; 32%) were previously misdiagnosed.

Conclusion

The clinical spectrum of ATTRwt is heterogeneous and differs from the classic phenotype: women are affected in a significant proportion; asymmetric LV hypertrophy and impaired LVEF are not rare and only a minority have low QRS voltages. Clinicians should be aware of the broad clinical spectrum of ATTRwt to correctly identify an entity for which a number of disease-modifying treatments are under investigation.

Prevalence of wild type ATTR assessed as myocardial uptake in bone scan in the elderly population

BACKGROUND

Myocardial uptake of bone tracers has emerged as useful tool for the early detection of transthyretin amyloidosis (ATTR). The prevalence of wild-type ATTR (ATTRwt) in individuals remains to be established.

METHODS

All whole body bone scans performed in individuals ≥ 75 years with no previous clinical suspicion of ATTR were revised in a population-based university hospital over a 7-year period (1509 studies corresponding to 1114 patients; 80.5 ± 4.1 years, 65% males). Positive cardiac uptake was defined according to Perugini score as grade 2 or 3. Heart failure (HF) hospitalizations during the follow-up were obtained from regional administrative databases.

RESULTS

Thirty-one patients ≥ 75 years (2.78%) showed cardiac uptake; compared with those without uptake, these patients were older (85 ± 5 vs. 80 ± 4, p < 0.001) and predominantly males (90% vs. 64%, p = 0.005). The prevalence of cardiac uptake was 3.88% in males and 0.77% in females, and increased with age, reaching 13.9% in males≥85 years (2.7% among females). The estimated prevalence for the European standard population ≥ 75 years was 4.15% in males, 1.03% in females and 2.59% in the general population. HF hospitalizations rates were 14% in patients without uptake and 29% in those with cardiac uptake (p = 0.034). After adjusting for age and gender, cardiac uptake was associated with a higher risk of HF hospitalization (OR 2.60, 95%CI 1.09-5.74, p = 0.022).

CONCLUSIONS

Myocardial uptake in bone scan is very prevalent with ageing, mainly affects males and is associated with an increased risk of HF hospitalization. These findings reinforce ATTRwt as a relevant cause of HF in the elderly.

Diagnostic accuracy of bone scintigraphy in the assessment of cardiac transthyretin-related amyloidosis: a bivariate meta-analysis

PURPOSE

Cardiac transthyretin-related amyloidosis (ATTR) is a progressive and fatal cardiomyopathy. The diagnosis of this disease is frequently delayed or missed due to the limited specificity of echocardiography. An increasing amount of data in the literature demonstrate the ability of bone scintigraphy with bone-seeking radiopharmaceuticals to detect myocardial amyloid deposits, in particular in patients with ATTR. Therefore we performed a systematic review and bivariate meta-analysis of the diagnostic accuracy of bone scintigraphy in patients with suspected cardiac ATTR.

METHODS

A comprehensive computer literature search of studies published up to 30 November 2017 on the role of bone scintigraphy in patients with ATTR was performed using the following search algorithm: (a) "amyloid" OR "amyloidosis" AND (b) "TTR" OR "ATTR" OR "transthyretin" AND (c) "scintigraphy" OR "scan" OR "SPECT" OR "SPET" OR "bone" OR "skeletal" OR "skeleton" OR "PYP" OR "DPD" OR "HMDP" OR "MDP" OR "HDP". Pooled sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-) and diagnostic odds ratio (DOR) of bone scintigraphy were calculated.

RESULTS

The meta-analysis of six selected studies on bone scintigraphy in cardiac ATTR including 529 patients provided the following results: sensitivity 92.2% (95% CI 89-95%), specificity 95.4% (95% CI 77-99%), LR+ 7.02 (95% CI 3.42-14.4), LR- 0.09 (95% CI 0.06-0.14), and DOR 81.6 (95% CI 44-153). Mild heterogeneity was found among the selected studies.

CONCLUSION

Our evidence-based data demonstrate that bone scintigraphy using technetium-labelled radiotracers provides very high diagnostic accuracy in the non-invasive assessment of cardiac ATTR.

Extracardiac 18F-florbetapir imaging in patients with systemic amyloidosis: more than hearts and minds

Purpose

¹⁸F-Florbetapir has been reported to show cardiac uptake in patients with systemic light-chain amyloidosis (AL). This study systematically assessed uptake of ¹⁸F-florbetapir in patients with proven systemic amyloidosis at sites outside the heart.

Methods

Seventeen patients with proven cardiac amyloidosis underwent ¹⁸F-florbetapir PET/CT imaging, 15 with AL and 2 with transthyretin amyloidosis (ATTR). Three patients had repeat scans. All patients had protocolized assessment at the UK National Amyloidosis Centre including imaging with ¹²³I-serum amyloid P component (SAP). ¹⁸F-Florbetapir images were assessed for areas of increased tracer accumulation and time–uptake curves in terms of standardized uptake values (SUV_mean) were produced.

Results

All 17 patients showed ¹⁸F-florbetapir uptake at one or more extracardiac sites. Uptake was seen in the spleen in 6 patients (35%; 6 of 9, 67%, with splenic involvement on ¹²³I-SAP scintigraphy), in the fat in 11 (65%), in the tongue in 8 (47%), in the parotids in 8 (47%), in the masticatory muscles in 7 (41%), in the lungs in 3 (18%), and in the kidney in 2 (12%) on the late half-body images. The ¹⁸F-florbetapir spleen retention index (SRI) was calculated. SRI >0.045 had 100% sensitivity/sensitivity (in relation to ¹²³I-SAP splenic uptake, the current standard) in detecting splenic amyloid on dynamic imaging and a sensitivity of 66.7% and a specificity of 100% on the late half-body images. Intense lung uptake was seen in three patients, one of whom had lung interstitial infiltration suggestive of amyloid deposition on previous high-resolution CT. Repeat imaging showed a stable appearance in all three patients suggesting no early impact of treatment response.

Conclusion

¹⁸F-Florbetapir PET/CT is a promising tool for the detection of extracardiac sites of amyloid deposition. The combination of uptake in the heart and uptake in the spleen on ¹⁸F-florbetapir PET/CT, a hallmark of AL, suggests that this tracer holds promise as a screening tool for AL.

Electronic supplementary material

The online version of this article (10.1007/s00259-018-3995-2) contains supplementary material, which is available to authorized users.

Can Nuclear Imaging Techniques Predict Patient Outcome and Guide Medical Management in Hereditary Transthyretin Cardiac Amyloidosis?

PURPOSE OF REVIEW

Nuclear imaging recently gained a key role in the diagnosis and prognostic assessment of transthyretin (TTR)-related cardiac amyloidosis. This review aims at summarizing the state-of-the art regarding the implementation of nuclear imaging in the management of hereditary mutated TTR-cardiac amyloidosis (mTTR-CA).

RECENT FINDINGS

Although cardiac uptake of bone tracers is acknowledged as a specific marker of TTR amyloid cardiac burden, recent studies validated the implementation of bone scan in the flow chart for non-invasive diagnosis and follow-up of CA in multicenter trials. Simultaneously, cardiac denervation evidenced by MIBG scintigraphy proved to be a strong and independent prognostic marker of poor outcome in mTTR-CA. By its unique ability to assess both amyloid burden and cardiac denervation, nuclear imaging may prove useful as part of multimodality imaging tools to trigger treatment initiation and monitoring in patients with mTTR-CA.

Cardiac denervation evidenced by MIBG occurs earlier than amyloid deposits detection by diphosphonate scintigraphy in TTR mutation carriers

PURPOSE

Cardiac involvement in familial transthyretin (TTR) amyloidosis is of major prognostic value, and the development of early-diagnostic tools that could trigger the use of new disease-modifying treatments is crucial. The aim of our study was to compare the respective contributions of ^99mTc-diphosphonate scintigraphy (DPD, detecting amyloid deposits) and ¹²³I-MIBG (MIBG, assessing cardiac sympathetic denervation) in patients with genetically proven TTR mutation referred for the assessment of cardiac involvement.

METHODS

We prospectively studied 75 consecutive patients (classified as symptomatic or asymptomatic carriers), using clinical evaluation, biomarkers (troponin and BNP), echocardiography, and nuclear imaging. Patients were classified as having normal heart-to-mediastinum (HMR) MIBG uptake ratio 4 h after injection (defined by HM4 ≥ 1.85) or abnormal HM4 < 1.85, and positive DPD uptake (grade ≥ 1 of Perugini classification) or negative DPD uptake.

RESULTS

Among 75 patients, 49 (65%) presented with scintigraphic sympathetic cardiac denervation and 29 (39%) with myocardial diphosphonate uptake. When MIBG was normal, DPD was negative except for two patients. Age was an independent predictor of abnormal scintigraphic result of both MIBG and DPD (HR 1.08 and 1.15 respectively), whereas echocardiographic-derived indicators of increased left ventricular filling pressure (E/e' ratio) was an independent predictor of abnormal MIBG (HR 1.33) and global longitudinal strain of positive DPD (HR 1.45). In asymptomatic patients (n = 31), MIBG was abnormal in 48% (n = 15) among whom 50% had a normal DPD; all those with a normal MIBG (n = 16) had a normal DPD.

CONCLUSIONS

In TTR mutation carriers, cardiac sympathetic denervation evidenced by decreased MIBG uptake is detected earlier than amyloid burden evidenced by DPD. These results raise the possibility of a diagnostic role for MIBG scintigraphy at an early stage of cardiac involvement in TTR-mutated carriers, in addition to its well-established prognostic value.

Recent advances in the noninvasive strategies of cardiac amyloidosis

The heart, like any organ in the body, is susceptible to amyloid deposition. Although more than 30 types of protein can cause amyloidosis, only two types commonly deposit in the ventricular myocardium: amyloid light chain and amyloid transthyretin. Amyloid cardiomyopathy is usually a major determinant of patient outcomes, and the diagnosis of heart involvement can be often relatively under-diagnosed, owing to nonspecific presenting symptoms and signs at a subclinical stage. The diagnosis of cardiac amyloidosis is usually performed by endomyocardial biopsy; however, the invasive nature and related high-risk complications restrict its wide use in clinical settings. Recently, with the advent of innovative techniques used for evaluating cardiac amyloidosis, noninvasive methods become increasingly important, especially in earlier diagnosis, distinguishing typing, risk prediction and response to treatment. Here, we will review recent developments in the noninvasive methods used in the assessment of cardiac amyloidosis, focused on the laboratory biomarkers and imaging modalities.

Early-phase myocardial uptake intensity of 99mTc-HMDP vs 99mTc-DPD in patients with hereditary transthyretin-related cardiac amyloidosis

BACKGROUND

This study sought to compare the intensity of early-phase myocardial uptake of two phosphonate-based radiotracers, 99mTc-hydroxymethylene diphosphonate (HMDP) and 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD), in patients with hereditary transthyretin-related cardiac amyloidosis (TTR-CA).

METHODS

Six patients with biopsy-proven diagnosis of TTR-CA and characteristic amyloid fibril composition underwent early-phase 99mTc-HMDP myocardial scintigraphy as part of their routine workup; they were later assessed by 99mTc-DPD scintigraphy after having signed informed written consent. Heart-to-mediastinum-ratio was measured at both time points as well as regional distribution on 17-segment analysis.

RESULTS

All patients had an H/M ratio >1.28 on both imaging. 99mTc-DPD uptake was slightly higher than 99mTc-HMDP uptake in 3 patients, but no statistical difference was found (P = 0.13). Regional distribution of the two radiotracers was well correlated on bull's eyes analysis, with only slight underestimation of 99mTc-DPD uptake in the anterior/apical segments, compared with 99mTc-HMDP.

CONCLUSION

99mTc-HMDP and 99mTc-DPD show comparable myocardial uptake intensity on early-phase scintigraphy and can be used alternatively for the diagnosis of TTR-CA.

Repeat doses of antibody to serum amyloid P component clear amyloid deposits in patients with systemic amyloidosis

Systemic amyloidosis is a fatal disorder caused by pathological extracellular deposits of amyloid fibrils that are always coated with the normal plasma protein, serum amyloid P component (SAP). The small-molecule drug, miridesap, [(R)-1-[6-[(R)-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC)] depletes circulating SAP but leaves some SAP in amyloid deposits. This residual SAP is a specific target for dezamizumab, a fully humanized monoclonal IgG1 anti-SAP antibody that triggers immunotherapeutic clearance of amyloid. We report the safety, pharmacokinetics, and dose-response effects of up to three cycles of miridesap followed by dezamizumab in 23 adult subjects with systemic amyloidosis (ClinicalTrials.gov identifier: NCT01777243). Amyloid load was measured scintigraphically by amyloid-specific radioligand binding of ¹²³I-labeled SAP or of ^99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid. Organ extracellular volume was measured by equilibrium magnetic resonance imaging and liver stiffness by transient elastography. The treatment was well tolerated with the main adverse event being self-limiting early onset rashes after higher antibody doses related to whole body amyloid load. Progressive dose-related clearance of hepatic amyloid was associated with improved liver function tests. ¹²³I-SAP scintigraphy confirmed amyloid removal from the spleen and kidneys. No adverse cardiac events attributable to the intervention occurred in the six subjects with cardiac amyloidosis. Amyloid load reduction by miridesap treatment followed by dezamizumab has the potential to improve management and outcome in systemic amyloidosis.

Targeted Nuclear Imaging Probes for Cardiac Amyloidosis

PURPOSE OF REVIEW

The aim of the present manuscript is to review the latest advancements of radionuclide molecular imaging in the diagnosis and prognosis of individuals with cardiac amyloidosis.

RECENT FINDINGS

^99mTechnetium labeled bone tracer scintigraphy had been known to image cardiac amyloidosis, since the 1980s; over the past decade, bone scintigraphy has been revived specifically to diagnose transthyretin cardiac amyloidosis. ¹⁸F labeled and ¹¹C labeled amyloid binding radiotracers developed for imaging Alzheimer's disease, have been repurposed since 2013, to image light chain and transthyretin cardiac amyloidosis. ^99mTechnetium bone scintigraphy for transthyretin cardiac amyloidosis, and amyloid binding targeted PET imaging for light chain and transthyretin cardiac amyloidosis, are emerging as highly accurate methods. Targeted radionuclide imaging may soon replace endomyocardial biopsy in the evaluation of patients with suspected cardiac amyloidosis. Further research is warranted on the role of targeted imaging to quantify cardiac amyloidosis and to guide therapy.

Regional Variation in Technetium Pyrophosphate Uptake in Transthyretin Cardiac Amyloidosis and Impact on Mortality

OBJECTIVES

This study sought to investigate the regional uptake of technetium 99m-pyrophosphate (TcPYP) in transthyretin cardiac amyloidosis (ATTR) and its association with mortality.

BACKGROUND

TcPYP nuclear scintigraphy is a diagnostic and prognostic tool in ATTR. Echocardiography has identified a pattern of regional variation in longitudinal strain (LS) with a gradient of improved strain from base to apex in ATTR.

METHODS

Consecutive patients with ATTR were evaluated who underwent TcPYP nuclear scintigraphy with planar and attenuation corrected single-photon emission computed tomography (SPECT). Heart-to-contralateral lung (H/CL) ratio was calculated on planar images, and left ventricular (LV) uptake was determined in each of the 17 segments using SPECT. A measure of apical-sparing of myocardial TcPYP uptake, termed the apical-sparing ratio (ASR), was calculated as basal + mid / apical counts.

RESULTS

Overall, 54 patients with ATTR (age 78 ± 9 years, 76% male, 31% hereditary ATTR) were analyzed. There was increased TcPYP uptake in basal and mid relative to apical LV segments, and an apical-sparing LS pattern on echocardiography. The right ventricle similarly showed greater uptake in basal segments. There were 26 deaths over 1.8 years median follow-up. The ASR of TcPYP uptake was associated with age-adjusted all-cause mortality (p = 0.013) with worse prognosis seen at levels <2.75. Global LS was also prognostic (p = 0.01), whereas H/CL ratio and total LV uptake indexed to blood pool were not (p = 0.772 and p = 0.850, respectively). The prognostic utility of the ASR persisted in multivariable modeling (p = 0.003), whereas global LS did not.

CONCLUSIONS

There is decreased TcPYP uptake in apical as compared to mid and basal segments in the LV, mimicking apical-sparing LS seen on echocardiography. Regional distribution of LV TcPYP uptake is associated with mortality, whereas overall amount of uptake as measured by H/CL ratio and indexed LV SPECT uptake is not.

Magnetic Resonance in Transthyretin Cardiac Amyloidosis

BACKGROUND

Cardiac transthyretin amyloidosis (ATTR) is an increasingly recognized cause of heart failure. Cardiac magnetic resonance (CMR), with late gadolinium enhancement (LGE) and T1 mapping, is emerging as a reference standard for diagnosis and characterization of cardiac amyloidosis.

OBJECTIVES

The authors used CMR with extracellular volume fraction (ECV) measurement to characterize cardiac involvement in relation to outcome in ATTR.

METHODS

Subjects comprised 263 patients with cardiac ATTR corroborated by grade 2 to 3 ^99mTc-DPD (^99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid) cardiac uptake, 17 with suspected cardiac ATTR (grade 1 ^99mTc-DPD), and 12 asymptomatic individuals with amyloidogenic transthyretin (TTR) mutations. Fifty patients with cardiac light-chain (AL) amyloidosis acted as disease comparators.

RESULTS

Unlike cardiac AL amyloidosis, asymmetrical septal left ventricular hypertrophy (LVH) was present in 79% of patients with ATTR (70% sigmoid septum and 30% reverse septal contour), whereas symmetrical LVH was present in 18%, and 3% had no LVH. In patients with cardiac amyloidosis, the pattern of LGE was always typical for amyloidosis (29% subendocardial, 71% transmural), including right ventricular LGE (96%). During follow-up (19 ± 14 months), 65 patients died. ECV independently correlated with mortality and remained independent after adjustment for age, N-terminal pro-B-type natriuretic peptide, ejection fraction, E/E', and left ventricular mass (hazard ratio: 1.164; 95% confidence interval: 1.066 to 1.271; p < 0.01).

CONCLUSIONS

Asymmetrical hypertrophy, traditionally associated with hypertrophic cardiomyopathy, was the commonest pattern of ventricular remodeling in ATTR. LGE imaging was typical in all patients with cardiac ATTR. ECV correlated with amyloid burden and was an independent prognostic factor for survival in this cohort of patients.

Genotype and Phenotype of Transthyretin Cardiac Amyloidosis: THAOS (Transthyretin Amyloid Outcome Survey)

BACKGROUND

Transthyretin amyloidosis (ATTR) is a heterogeneous disorder with multiorgan involvement and a genetic or nongenetic basis.

OBJECTIVES

The goal of this study was to describe ATTR in the United States by using data from the THAOS (Transthyretin Amyloidosis Outcomes Survey) registry.

METHODS

Demographic, clinical, and genetic features of patients enrolled in the THAOS registry in the United States (n = 390) were compared with data from patients from other regions of the world (ROW) (n = 2,140). The focus was on the phenotypic expression and survival in the majority of U.S. subjects with valine-to-isoleucine substitution at position 122 (Val122Ile) (n = 91) and wild-type ATTR (n = 189).

RESULTS

U.S. subjects are older (70 vs. 46 years), more often male (85.4% vs. 50.6%), and more often of African descent (25.4% vs. 0.5%) than the ROW. A significantly higher percentage of U.S. patients with ATTR amyloid seen at cardiology sites had wild-type disease than the ROW (50.5% vs. 26.2%). In the United States, 34 different mutations (n = 201) have been reported, with the most common being Val122Ile (n = 91; 45.3%) and Thr60Ala (n = 41; 20.4%). Overall, 91 (85%) of 107 patients with Val122Ile were from the United States, where Val122Ile subjects were younger and more often female and black than patients with wild-type disease, and had similar cardiac phenotype but a greater burden of neurologic symptoms (pain, numbness, tingling, and walking disability) and worse quality of life. Advancing age and lower mean arterial pressure, but not the presence of a transthyretin mutation, were independently associated with higher mortality from a multivariate analysis of survival.

CONCLUSIONS

In the THAOS registry, ATTR in the United States is overwhelmingly a disorder of older adult male subjects with a cardiac-predominant phenotype. Val122Ile is the most common transthyretin mutation, and neurologic phenotypic expression differs between wild-type disease and Val122Ile, but survival from enrollment in THAOS does not. (Transthyretin-Associated Amyloidoses Outcome Survey [THAOS]; NCT00628745).

Transthyretin amyloidosis: an under-recognized neuropathy and cardiomyopathy

Transthyretin (TTR) amyloidosis (ATTR amyloidosis) is an underdiagnosed and important type of cardiomyopathy and/or polyneuropathy that requires increased awareness within the medical community. Raising awareness among clinicians about this type of neuropathy and lethal form of heart disease is critical for improving earlier diagnosis and the identification of patients for treatment. The following review summarizes current criteria used to diagnose both hereditary and wild-type ATTR (ATTRwt) amyloidosis, tools available to clinicians to improve diagnostic accuracy, available and newly developing therapeutics, as well as a brief biochemical and biophysical background of TTR amyloidogenesis.

Transthyretin Cardiac Amyloidosis in Older Adults: Optimizing Cardiac Imaging to the Corresponding Diagnostic and Management Goal

PURPOSE OF REVIEW

Transthyretin cardiac amyloidosis is increasingly recognized as an important cause of heart failure in older adults. Many cardiac imaging modalities have evolved to evaluate transthyretin cardiac amyloidosis and include 2D echocardiography with tissue Doppler and speckle-strain imaging, nuclear scintigraphy, cardiac magnetic resonance imaging, and positron emission tomography. The purpose of this review is to highlight the optimal selection of advanced cardiac imaging techniques with corresponding diagnostic goals including raising suspicion, making an early diagnosis, and subtyping transthyretin cardiac amyloid, as well as management goals including assessment of ventricular impairment, prognosticating, and monitoring disease progression. Potential benefits of optimizing cardiac imaging in the elderly patient with transthyretin cardiac amyloidosis may include enhanced and earlier diagnosis and refined long-term management.

RECENT FINDINGS

Advances in cardiac imaging techniques are changing diagnostic and management algorithms for transthyretin cardiac amyloidosis.

SUMMARY

With a new era of novel therapeutics, enhanced recognition, and earlier diagnosis approaching, selecting the appropriate non-invasive cardiac imaging modality will be essential for optimal care in the elderly patient with transthyretin cardiac amyloidosis.

Occult Transthyretin Cardiac Amyloid in Severe Calcific Aortic Stenosis: Prevalence and Prognosis in Patients Undergoing Surgical Aortic Valve Replacement

BACKGROUND

Calcific aortic stenosis (cAS) affects 3% of individuals aged >75 years, leading to heart failure and death unless the valve is replaced. Wild-type transthyretin cardiac amyloid is also a disorder of ageing individuals. Prevalence and clinical significance of dual pathology are unknown. This study explored the prevalence of wild-type transthyretin amyloid in cAS by myocardial biopsy, its imaging phenotype and prognostic significance.

METHODS AND RESULTS

A total of 146 patients with severe AS requiring surgical valve replacement underwent cardiovascular magnetic resonance and intraoperative biopsies; 112 had cAS (75±6 years; 57% men). Amyloid was sought histologically using Congo red staining and then typed using immunohistochemistry and mass spectrometry; patients with amyloid underwent clinical evaluation including genotyping and (99m)TC-3,3-diphosphono-1,2-propanodicarboxylic-acid (DPD) bone scintigraphy. Amyloid was identified in 6 of 146 patients, all with cAS and >65 years (prevalence 5.6% in cAS >65). All 6 patients had wild-type transthyretin amyloid (mean age 75 years; range, 69-85; 4 men), not suspected on echocardiography. Cardiovascular magnetic resonance findings were of definite cardiac amyloidosis in 2, but could be explained solely by AS in the other 4. Postoperative DPD scans demonstrated cardiac localization in all 4 patients who had this investigation (2 died prior). At follow-up (median, 2.3 years), 50% with amyloid had died (versus 7.5% in cAS; 6.9% in age >65 years). In univariable analyses, the presence of transthyretin amyloidosis amyloid had the highest hazard ratio for death (9.5 [95% confidence interval, 2.5-35.8]; P=0.001).

CONCLUSIONS

Occult wild-type transthyretin cardiac amyloid had a prevalence of 6% among patients with AS aged >65 years undergoing surgical aortic valve replacement and was associated with a poor outcome.

A case study of likely wild-type cardiac transthyretin amyloidosis causing rapid deterioration

We present the case of an 88-year-old gentleman who presented to hospital septic with bilateral leg cellulitis, pulmonary oedema and hypotension. He had no history of heart disease but had had bilateral carpal tunnel releases. His condition deteriorated with refractory hypotension in spite of fluid filling, inotropic and vasopressor support. His echocardiogram showed an infiltrative cardiomyopathy with a speckled myocardium, severe concentric left and right ventricular increased wall thickness, diastolic dysfunction, biatrial dilatation and restrictive physiology in keeping with cardiac amyloidosis. He developed atrial fibrillation and worsening respiratory failure due to fluid overload and was intubated and ventilated but continued to decline and passed away. The degree of heart failure in the absence of ischaemia, the patient's advanced age, echocardiographic findings and past history of carpal tunnel syndrome in a male are strongly indicative of a diagnosis of wild-type cardiac transthyretin amyloidosis. We discuss the key features and intensive care management of this disease.

Addressing Common Questions Encountered in the Diagnosis and Management of Cardiac Amyloidosis

Advances in cardiac imaging have resulted in greater recognition of cardiac amyloidosis in everyday clinical practice, but the diagnosis continues to be made in patients with late-stage disease, suggesting that more needs to be done to improve awareness of its clinical manifestations and the potential of therapeutic intervention to improve prognosis. Light chain cardiac amyloidosis, in particular, if recognized early and treated with targeted plasma cell therapy, can be managed very effectively. For patients with transthyretin amyloidosis, there are numerous therapies that are currently in late-phase clinical trials. In this review, we address common questions encountered in clinical practice regarding etiology, clinical presentation, diagnosis, and management of cardiac amyloidosis, focusing on recent important developments in cardiac imaging and biochemical diagnosis. The aim is to show how a systematic approach to the evaluation of suspected cardiac amyloidosis can impact the prognosis of patients in the modern era.

One mutation, two distinct disease variants: unravelling the impact of transthyretin amyloid fibril composition

Although hereditary transthyretin (h-ATTR) amyloidosis is a monogenetic disease, a large variation in its phenotype has been observed. The common hypothesis of amyloid fibril formation involves dissociation of the transthyretin (TTR) tetramer into monomers that after misfolding reassemble into amyloid fibrils. This notion is partly challenged by the finding of two distinct types of amyloid fibrils. One of these, type A, consists of C-terminal ATTR fragments and full-length TTR, whereas the other, type B, consists only of full-length TTR. All organs of an individual patient contain ATTR deposits of either type A or type B fibrils, and the composition in each individual remains unchanged over time. The finding of two distinct types of ATTR fibrils suggests that there are at least two different pathways in operation for ATTR fibril formation. For the most common European mutation, TTR Val30Met, ATTR fibril composition is related to the outcome of liver transplantation, which is the first successful treatment for the disease, and the penetrance of the trait. In addition, the presence of C-terminal ATTR fragments has an impact on the affinity for various tracers used for noninvasive imaging of amyloid depositions such as 99 m-technetium-diphosphono-propanodicarboxylic acid scintigraphy and positron emission tomography utilizing Pittsburgh component B, and even for the gold standard diagnostic procedure, tissue biopsy stained by Congo red and examined under polarized light. The importance of amyloid fibril composition needs to be taken into consideration when designing clinical trials of treatment modalities, and also in the evaluation of diagnostic methods such as imaging techniques.

The Utility of 99mTc-DPD Scintigraphy in the Diagnosis of Cardiac Amyloidosis: An Australian Experience

BACKGROUND

The uptake of bone-seeking radiotracers in the amyloid heart is well recognised. 99^mTc-DPD has been shown to be highly sensitive for cardiac transthyretin (ATTR) amyloid in an overseas population, but is not registered for use in Australia. We explored its utility as a diagnostic tool within our population.

METHODS

Patients diagnosed with AL and ATTR (wild-type and inherited) cardiac amyloidosis were prospectively recruited from the Princess Alexandra Hospital Amyloidosis Centre. Patients underwent injection with ^99mTc-DPD then planar whole body imaging was performed at 5 minutes post-injection (soft tissue phase) and 3 hours (bone phase). A myocardial SPECT and low amperage CT were acquired after the late whole-body scan. Scans were analysed by two nuclear imaging specialists. Intensity of cardiac ^99mTc-DPD uptake was graded as 0 to 3 in accordance with previous criteria, and semiquantitative analysis was performed using a heart to whole body ratio (H:WB) on the 3-hour scan. Patients also underwent electrocardiography and transthoracic echocardiography, and blood samples were taken for troponin I and brain natriuretic peptide levels, to assess for any correlation with DPD uptake.

RESULTS

Twenty-one patients (8 AL and 13 ATTR) completed the study. Median age was 58 and 70 years for AL and ATTR patients respectively, and 19 (90.5%) were male. 99^mTc-DPD scintigraphy was positive in 2 (25%) of AL, and 13 (100%) of ATTR patients. Grade of cardiac uptake, and mean H:WB (0.1249 v. 0.0794) was greater in the ATTR cohort (p-value<0.001 and 0.001 respectively). No statistically significant correlation was identified between H:WB and echocardiographic parameters. There was a significant positive correlation between H:WB and the PR interval on ECG (p=0.026).

CONCLUSIONS

99^mTc-DPD scintigraphy is highly sensitive for the diagnosis of cardiac ATTR amyloid, but less so for AL amyloid.

Liver dysfunction as predictor of prognosis in patients with amyloidosis: utility of the Model for End-stage Liver disease (MELD) scoring system

Amyloidosis prognosis is often related to the onset of heart failure and a worsening that is concomitant with kidney-liver dysfunction; thus the Model for End-stage Liver disease (MELD) may be an ideal instrument to summarize renal-liver function. Our aim has been to test the MELD score as a prognostic tool in amyloidosis. We evaluated 128 patients, 46 with TTR-related amyloidosis and 82 with AL amyloidosis. All patients had a complete clinical and echocardiography evaluation; overall biohumoral assessment included troponin I, NT-proBNP, creatinine, total bilirubin and INR ratio. The study population was dichotomized at the 12 cut-off level of MELD scores; those with MELD score >12 had a lower survival compared to controls in the study cohort (40.7 vs 66.3 %; p = 0.006). Either as a continuous and dichotomized variable, MELD shows its independent prognostic value at multivariable analysis (HR = 1.199, 95 % CI 1.082-1.329; HR = 2.707, 95 % CI 1.075-6.817, respectively). MELD shows a lower prognostic sensitivity/specificity ratio than troponin I and NT-proBNP in the whole study population and AL subgroup, while in TTR patients MELD has a higher sensitivity/specificity ratio compared to troponin and NT-proBNP (ROC analysis-AUC: 0.853 vs 0.726 vs 0.659). MELD is able to predict prognosis in amyloidosis. A MELD score >12 selects a subgroup of patients with a higher risk of death. The predictive accuracy seems to be more evident in TTR patients in whom currently no effective scoring systems have been validated.

Transthyretin Cardiac Amyloidosis in Older Americans

Wild-type transthyretin cardiac amyloidosis (ATTRwt), formerly called senile cardiac amyloidosis (SCA), is almost exclusively a disorder of older adults. As the population ages, the diagnosis of ATTRwt will increase, making it the most common form of cardiac amyloidosis. An important precondition to reduce underdiagnosis and misdiagnosis is to maintain a high index of suspicion for cardiac amyloidosis. Several clues can be gleaned from the clinical history, physical exam, electrocardiography, and noninvasive imaging techniques. Nuclear scintigraphy agents using 99mTc-phosphate derivatives combined with assessment for monoclonal proteins are eliminating the need for tissue confirmation in ATTR. Morbidity and mortality from ATTRwt cardiac amyloid is high and the emergence of numerous therapies based on a biologic understanding of the pathophysiology of this condition, including drugs to inhibit the synthesis of TTR, stabilize TTR, and degrade or extract amyloid, provides new hope for those afflicted. This review briefly covers the epidemiology, pathophysiology, and clinical manifestations, as well as diagnostic strategies and treatment, of ATTR in older adults.

Varying levels of small microcalcifications and macrophages in ATTR and AL cardiac amyloidosis: implications for utilizing nuclear medicine studies to subtype amyloidosis

BACKGROUND

Recently, there has been much interest in using nuclear medicine studies to noninvasively identify and subtype cardiac amyloidosis. In particular, modified bone scans using (99m)Tc-3,3-diphosphono-1,2-propanodicarboxylic acid ((99m)Tc-DPD) and (99m)Tc-pyrophosphate ((99m)Tc-PYP) are being used to selectively identify patients with ATTR amyloidosis rather than AL amyloidosis. The morphologic basis underlying the selectivity of these imaging modalities for ATTR amyloidosis has been unclear.

METHODS

To determine if variations in microcalcifications and/or macrophages within ATTR and AL amyloidosis might be responsible for the selectivity for these imaging modalities, 8 endomyocardial biopsies of ATTR amyloidosis and 7 endomyocardial biopsies of AL amyloidosis were stained with von Kossa calcium stains and with immunohistochemistry for the macrophage marker CD68.

RESULTS

Compared with AL amyloidosis, there was a greater density of small microcalcifications in cases of ATTR amyloidosis (mean=16.8 vs. 6.5 per 200× field, P=.008). In contrast, there were fewer macrophages in ATTR amyloidosis compared with AL amyloidosis (mean=2.5 vs. 11.7 per 200× field, P=.0004). The density of microcalcifications within each group was not related to patient age, echocardiographic features of cardiac function, or serum levels of calcium and creatinine.

CONCLUSIONS

These data suggest that microcalcifications but not macrophages likely underlie the selectivity of modified bone scans for ATTR amyloidosis and suggest that other pathologic entities containing microcalcifications might also result in positive scans with these imaging modalities.

Systemic amyloidosis

Tissue deposition of protein fibrils causes a group of rare diseases called systemic amyloidoses. This Seminar focuses on changes in their epidemiology, the current approach to diagnosis, and advances in treatment. Systemic light chain (AL) amyloidosis is the most common of these conditions, but wild-type transthyretin cardiac amyloidosis (ATTRwt) is increasingly being diagnosed. Typing of amyloid fibrils, a critical determinant of therapy, has improved with the wide availability of laser capture and mass spectrometry from fixed histological tissue sections. Specific and accurate evaluation of cardiac amyloidosis is now possible using cardiac magnetic resonance imaging and cardiac repurposing of bone scintigraphy tracers. Survival in AL amyloidosis has improved markedly as novel chemotherapy agents have become available, but challenges remain in advanced disease. Early diagnosis, a key to better outcomes, still remains elusive. Broadening the amyloid-specific therapeutic landscape to include RNA inhibitors, fibril formation stabilisers and inhibitors, and immunotherapeutic targeting of amyloid deposits holds promise to transform outcomes in systemic amyloidoses.