Amyloidosis—the Diagnosis and Treatment of an Underdiagnosed Disease

Background: Systemic amyloidosis is a multi-system disease caused by fibrillary protein deposition with ensuing dysfunction of the affected organ systems. Its diagnosis is often delayed because the manifestations of the disease are variable and non-specific. Its main forms are light chain (AL) amyloidosis and transthyretin-related ATTR amyloidosis, which, in turn, has both a sporadic subtype (wildtype, ATTRwt) and a hereditary subtype (mutated, ATTRv).

Methods: This review is based on pertinent publications that were retrieved by a selective search in PubMed covering the years 2005 to 2019.

Results: No robust epidemiological figures are available for Germany to date. Both AL amyloidosis and hereditary ATTR amyloidosis are rare diseases, but the prevalence of ATTRwt amyloidosis is markedly underestimated. The diagnostic algorithm is complex and generally requires histological confirmation of the diagnosis. Only cardiac ATTR amyloidosis can be diagnosed non-invasively with bone scintigraphy once a monoclonal gammopathy has been excluded. AL amyloidosis can be considered a complication of a plasma cell dyscrasia and treated with reference to patterns applied in multiple myeloma. Despite the availability of causally directed treatment, it has not yet been possible to reduce the mortality of advanced cardiac AL amyloidosis. Three drugs (tafamidis, patisiran, and inotersen) are now available to treat grade 1 or 2 polyneuropathy in ATTRv amyloidosis, and further agents are now being tested in clinical trials. It is expected that tafamidis will soon be approved in Germany for the treatment of cardiac ATTR amyloidosis.

Conclusion: The diagnosis of amyloidosis is difficult because of its highly varied presentation. In case of clinical suspicion, a rapid, targeted diagnostic evaluation and subsequent initiation of treatment should be performed in a specialized center. When the new drugs to treat amyloidosis become commercially available, their use and effects should be documented in nationwide registries.

The term systemic amyloidosis embraces a number of heterogeneous syndromes characterized by protein deposits in the form of insoluble fibrils in the patient’s tissues (1). The clinical findings vary according to the identity of the protein concerned and the extent and pattern of organ involvement (1, 2). As yet there are no valid epidemiological data for systemic amyloidosis in Germany. Light chain (AL) amyloidosis is so far considered to be the most frequently occurring form (1, 3), with an incidence of 8.9–12.7/million person-years and prevalence of 40–58/million person-years (4). Hereditary transthyretin (ATTRv) amyloidosis is estimated to affect 5000–10 000 persons worldwide (5). These figures meet the definition of a rare disease. In contrast, age-related wild-type transthyretin (ATTRwt) amyloidosis is being diagnosed increasingly often: 25% of patients with heart failure with preserved left ventricular ejection fraction (HFpEF) over 80 and 13% of those over 60 years of age are thought to be affected (6, 7). This means that the prevalence has been underestimated.

This article reviews the data on systemic amyloidosis, focusing on the prognostic relevance of cardiac involvement, on diagnosis of the disease, and on the spectrum of emerging treatment concepts.

Methods

We carried out a selective search of PubMed for pertinent records published in the period 2005–2019. The search terms were “systemic amyloidosis,” “AL amyloidosis,” “ATTR amyloidosis,” “senile systemic amyloidosis,” “cardiac amyloidosis,” “familial amyloid polyneuropathy,” and “familial amyloid cardiomyopathy.”

eMethods

Pathophysiology

Systemic amyloidosis arises from the formation of insoluble amyloid fibrils, which in turn results from deposition of misfolded proteins. Over 30 proteins are known to be involved (8), causing different subtypes that cannot be distinguished by clinical means.

• AL amyloidosis: This results from the deposition of monoclonal free light chains—systemically due to monoclonal gammopathy, multiple myeloma, or, more rarely, B-cell lymphoma, or locally due to local production of light chains. In systemic manifestations, circulating light chains have a direct cardiotoxic action (1). Deposits of light chains lead to mechanical interference and have cytotoxic and proapoptotic effects (1).
• ATTR amyloidosis: The causal protein is transthyretin (TTR), the transport protein of thyroxine and retinol-binding protein/vitamin A (9). Although the underlying mechanism has not been fully elicited (10), the essential feature seems to be mechanical/enzymatic cleavage of fragments from the TTR tetramer by proteases. This leads to destabilization and misfolding of the monomers with tissue deposition triggered by C-terminal fragments (10). Furthermore, amyloidogenic TTR mutations facilitate the deposition process in ATTRv amyloidosis by increasing thermodynamic instability (11). Besides mutant TTR, the deposits in patients with ATTRv amyloidosis also contain wild-type TTR (12). Altogether, more than 120 causal mutations have been identified, typically inherited in an autosomal dominant fashion with variable penetrance. Analogously, natural TTR is co-deposited in ATTRwt amyloidosis (9).

Clinical findings

The clinical manifestations of amyloidosis vary widely depending on the subtype and on the pattern and severity of organ involvement (Table). Owing to low specificity, prodromes are frequently misinterpreted—typically as symptoms of a common illness. Diagnosis is often delayed: 20% of patients with AL amyloidosis are not correctly diagnosed until 2 years or longer after the first symptoms, and in 42% of those with cardiac ATTRwt amyloidosis the diagnostic process takes more than 4 years (13, 14). Findings that should serve as “red flags” for continued diagnostic efforts include nephrotic syndrome, HFpEF, rapidly progressive polyneuropathy, unexplained hepatomegaly or diarrhea, unexplained weight loss, and otherwise inexplicable elevation of cardiac biomarkers in plasma cell dyscrasia (3).

Table

The clinical manifestations of systemic amyloidosis

The manifestations of AL amyloidosis are primarily cardiac (about 75–80%) and renal (about 65%); less frequently, the soft tissues (15%), the liver (15%), the nervous system (10%), and the gastrointestinal tract (5%) are involved. Cardiac involvement worsens the prognosis (1). Typically, AL amyloidosis progresses rapidly and thus demands immediate diagnosis and treatment. Around 30% of patients diagnosed with advanced cardiac amyloidosis die within one year, and so far the effective new treatment options have not decreased this early mortality (1). The 4-year survival rate varies between 40% and 60% (1).

ATTRwt amyloidosis frequently presents with a cardiac phenotype in the form of slowly progressing HFpEF (15). There is often accompanying neurological involvement, e.g., symmetric, extremely variable sensorimotor polyneuropathy, but purely neurological manifestations are rare (4%). ATTRwt amyloidosis is known to be associated with carpal tunnel syndrome and lumbar spinal stenosis. Men are predominantly affected. The median duration of survival after diagnosis is about 4 years (15).

Depending on the mutation, the phenotype of ATTRv amyloidosis is predominantly cardiac, neuropathic, or mixed cardiac/neuropathic (16). Much more infrequently, the kidney, gastrointestinal tract, eye, leptomeninges/meninges, or vascular system (amyloidangiopathy) are involved.

Diagnosis

The diagnosis of amyloidosis is a multi-stage process that should take place without delay (10).

Histological confirmation of suspected amyloidosis

Histological demonstration of amyloidosis is essential for confirmation of the diagnosis. A suitable low-invasive procedure is aspiration of abdominal fat, the sensitivity of which depends on the subtype of amyloidosis concerned (84% for cardiac AL amyloidosis, 15% for cardiac ATTRwt amyloidosis, 45% for cardiac ATTRv amyloidosis (17). If the result is negative, salivary gland biopsy should follow (18). Direct organ biopsy should be resorted to only if the diagnosis remains uncertain or in the presence of a constellation such as isolated cardiac involvement with coexisting monoclonal gammopathy.

Cardiac ATTR amyloidosis in the absence of monoclonal gammopathy (negative immunofixation from serum and 24-h urine together with normal levels of free light chains) is the only subtype amenable to noninvasive diagnosis by means of skeletal scintigraphy (sensitivity > 99%, specificity 86%) (19).

Suitable tracers are ^99mTc-DPD, ^99mTc-PYP, and ^99mTc-HMDP (10). Cardiac involvement in ApoAI and AA amyloidosis might result in positive scintigraphy as well (10).

Amyloid subtyping and mutation analysis

Amyloid subtyping from a tissue sample obtained by biopsy is obligatory, particularly because the presence of a monoclonal gammopathy does not prove the existence of AL amyloidosis: in 20% of cases, ATTR amyloidosis is accompanied by monoclonal gammopathy (19). The subtyping can be achieved by means of mass spectroscopy, immunohistochemistry (NB: higher error rate), or immunoelectron microscopy in a special laboratory with suitably experienced personnel. Should a potentially hereditary form of amyloidosis be demonstrated, the corresponding gene must be analyzed for mutations.

Characterization of organ involvement

Precise characterization of the extent and severity of organ involvement is essential, especially for treatment planning in cases of AL amyloidosis (1). The diagnosis of cardiac involvement in a patient with extracardiac detection of amyloid rests on otherwise inexplicable elevation of the cardiac biomarkers N-terminal prohormone brain-natriuretic peptide (NT-proBNP) and troponin, together with characteristic morphological features on diagnostic imaging. The grading of cardiac involvement is based primarily on NT-proBNP and troponin (1, 2, 10, 15). Renal manifestations are marked by proteinuria with predominant albuminuria, and impairment of renal function. Isolated elevation of alkaline phosphatase and hepatomegaly point to involvement of the liver.

Figure 1 shows a detailed diagnostic algorithm for patients suspected to have cardiac amyloidosis. The order in which investigations are carried out and the appraisal of the findings is complex, so the diagnostic investigations should take place at a specialized center. In particular, such a facility should be contacted at the first suspicion of cardiac AL amyloidosis owing to the prognostic import of heart involvement.

Figure 1

Diagnostic algorithm

Treatment

AL amyloidosis

In principle, AL amyloidosis can be understood as a complication of plasma cell dyscrasia. It is treated with reference to treatment patterns applied to multiple myeloma, i.e. targeting rapid elimination of the amyloidogenic, (cardio)toxic light chains.

Patients can be risk-stratified into “fit” and “fragile” on the basis of clearly defined parameters of suitability for high-dose chemotherapy (Figure 2).

Figure 2

Treatment algorithm for systemic AL amyloidosis

“Fit” patients (10–25%) should receive high-dose chemotherapy. Induction chemotherapy is necessary only if the initial plasma cell infiltration of bone marrow is >10% or the CRAB criteria (hypercalcemia, renal insufficiency, anemia, bone lesions) are fulfilled. Usually, a single administration of high-dose chemotherapy follows stem-cell mobilization with granulocyte colony-stimulating factor (GCSF) without chemotherapy beforehand. Particularly patients with known translocation t(11;14) profit from the high-dose chemotherapy concept/high-dose melphalan, while a poorer response has been reported for bortezomib-based protocols (20, 21).

A proteasome inhibitor-based regimen has become established for “fragile” patients. For younger patients, CyBorD (bortezomib, cyclophosphamide, dexamethasone) should be preferred to BMDex (bortezomib, melphalan, dexamethasone) owing to the stem cell toxicity of melphalan, in order to retain the option of stem cell apheresis and high-dose chemotherapy at a later date (1). MDex is an effective treatment option in polyneuropathy and gain of chromosome 1q21 (1, 22).

Patients who do not respond adequately to their first-line treatment should be switched to daratumumab, a monoclonal anti-CD38 antibody.

In the event of renewed or increasing disease activity after completion of the first-line treatment, the latter can be repeated. Alternatively, immunomodulator (IMiD)-based protocols (particularly lenalidomide [Revlimid] and pomalidomide) or daratumumab can be used (3). The recently introduced proteasome inhibitors such as ixazomib may represent an alternative (23). Further therapeutic agents are in clinical testing.

Dose-reduced (standard) protocols may be necessary in very advanced disease. In young patients, organ transplantation before initiation of chemotherapy can be considered in order to render them amenable to treatment.

In AL amyloidosis, a hematological response is distinguished from a response at organ level (Figure 3). Hematological response means a decrease in serological activity corresponding to a decrease in the free light chain difference; ideally, negative immunofixation in blood and (24-h) urine with normal levels of free light chains in serum. Organ response means functional improvement of the organs involved, which may in some cases be delayed until a number of months after the onset of hematological response (24). The treatment response should always be assessed every two to three cycles and, if required, the treatment adjusted. Treatment can be ended two cycles after the peak response (1).

Figure 3

Assessment of treatment response in systemic AL amyloidosis

If the response is inadequate, the treatment must be modified immediately.

Hereditary ATTR amyloidosis

For many years the only treatment for ATTRv amyloidosis was liver transplantation (25), but this is no longer the case. The 20-year survival rate after liver transplantation was 55% in an international analysis of 1940 patients with ATTRv amyloidosis from 19 countries (25). Important for the prognosis is timely recognition of the indication for transplantation and the absence of severe organ-related manifestations at the time of surgery (26). The fully functional explanted liver of a patient with ATTRv amyloidosis can be donated to another patient who would otherwise not receive a replacement organ (domino transplantation) (10). However, the transplant recipient runs the risk of iatrogenic ATTRv amyloidosis (10).

The primary aim of more recently introduced treatments is to slow down or halt disease progression by means of gene silencing strategies, TTR stabilization, and depletion of existing amyloid deposits (Figure 4). A detailed overview of selected studies, some published and others still recruiting patients, can be found in the eTable.

Figure 4

Treatment approaches for ATTR amyloidosis

eTable

Treatment approaches and selected study results in ATTR amyloidosis

Gene silencers inhibit hepatic synthesis of the causal TTR protein by mRNA interference (eBox). Only patisiran and inotersen have so far been approved for use in patients who have ATTRv amyloidosis with polyneuropathy grade I or II, while no agents have yet been licensed for cardiac involvement.

eBox

mRNA interference

Patisiran, an siRNA, was investigated in the randomized, double-blinded, placebo-controlled APOLLO trial (phase III) of 225 ATTRv amyloidosis patients with polyneuropathy. After 18 months, the verum group showed improvement of 6.0 ± 0.7 points in the modified Neuropathy Impairment Score (mNIS + 7), the primary endpoint, while the control group score worsened by 28.0 ± 2.6 points (p <0.001) (27). Secondary endpoints were also more favorable in the patisiran group, for example quality of life (Norfolk QoL-DN; difference −21.1 points; p <0.001), speed in the 10-m walking test (difference +0.31 m/s; p <0.001), and nutritional status (modified BMI; difference +116; p <0.001). In the echocardiographic substudy (56% of the study population), patients who were given patisiran showed a consistent decrease in mean wall thickness (difference 0.9 mm, p = 0.017); signs of increased end-diastolic volume and stroke volume; and a decrease in global longitudinal strain. Heart-related hospitalizations and overall mortality were lower with patisiran than with placebo (18.7 versus 10.1 events per 100 patient-years) (28). Patisiran is administered intravenously every 3 weeks. Infusion reactions constitute the principal adverse effect.

Inotersen, an antisense oligonucleotide, was investigated in 172 patients in the phase-III NEURO-TTR study. With regard to the primary endpoints, patients who were given inotersen showed slower disease progression as measured by the mNIS + 7 (difference −19.7 points; p <0.001) and better development of quality of life (difference in Norfolk QoL-DN score −11.7 points; p <0.001) (29). Inotersen is administered subcutaneously once a week. The clinically relevant adverse effects are glomerulonephritis (3 %) and thrombopenia (3 %), necessitating regular laboratory monitoring.

The multicenter, double-blind, placebo-controlled phase-III trial of revusiran in patients with manifestations of cardiac ATTRv amyloidosis showed increased overall and cardiovascular mortality in the revusiran arm.

Other newly developed therapeutics are long-acting subcutaneously administered substances: Vutrisiran is a so-called enhanced stability chemistry (ESC) GalNAc conjugate with better hepatic uptake which, compared with patisiran, promises greater efficacy and better stability despite a lower administration volume.

The randomized phase-III trial HELIOS-A is comparing the efficacy and safety of vutrisiran (25 mg subcutaneously every 3 months) and patisiran in ATTRv patients with neurological manifestations (NCT03759379). The complementary phase-III trial HELIOS-B for cardiac manifestations is at the recruitment stage (NCT04153149).

AKCEA-TTR-LRx (ION-682884) is a GalNAc₃ antisense oligonucleotide conjugate with greater stability than inotersen, better hepatic uptake, and higher efficacy, enabling monthly subcutaneous administration. The phase-III trials on neurological and cardiac manifestations (NEURO-TTRansform [NCT04136184] and CARDIO-TTRansform [NCT04136171], respectively) are currently recruiting.

Stabilization of the transthyretin tetramer can be achieved particularly with tafamidis (30), diflunisal (31), AG-10 (32), and tolcapone (33). The only TTR stabilizer licensed for use in Germany is tafamidis for ATTRv patients with grade I polyneuropathy; approval for cardiac ATTRv amyloidosis is expected in 2020. Tafamidis occupies the thyroxine binding site, thus preventing TTR tetramer dissociation. It is given orally and its primary effect is to slow the progress of the disease (34, 35). Administration at an early stage in the disease course is crucial. In the randomized, double-blind, phase-III ATTR-ACT trial on patients with cardiac ATTR amyloidosis (ATTRwt and ATTRv), tafamidis significantly decreased the overall mortality (hazard ratio 0.70; 95% confidence interval [0.51; 0.96]) and the number of cardiovascular-related hospitalizations (0.48 vs. 0.70/year) (36). The adverse effects were comparable with those in the placebo group (36). Diflunisal was found to slow the progression of neurological manifestations compared with placebo (increase of 25 points in NIS + 7 score; difference 16 points, p < 0.001). The data regarding the efficacy of diflunisal in ATTR cardiomyopathy come from a small Japanese study (n = 40, ATTRv amyloidosis, 24 months’ observation) which showed signs of stabilization of cardiac wall thickness.

A pilot study of another new TTR stabilizer, tolcapone, has recently shown TTR stabilization in all participants (NCT02191826), but phase-III data are lacking. Because tolcapone penetrates the blood–brain barrier, its short-term TTR-stabilizing effects have been investigated in an early phase-I study in patients with symptomatic and asymptomatic leptomeningeal involvement; however, the results have not yet been published (NCT03591757).

Doxycycline/tauroursodeoxycholic acid (TUDCA) targets acceleration of fibril degeneration and fibril resorption (37). The studies conducted to date have small case numbers and suggest a positive effect in patients with cardiac involvement. A larger randomized, placebo-controlled phase-III trial in patients with ATTRwt and ATTRv amyloidosis is now recruiting (NCT03481972). Other substances currently being tested include the monoclonal antibody PRX004, directed against monomers and deposited TTR amyloid (38).

The potential significance of the novel treatments is not yet clear—no studies comparing them directly have been published. According to an expert recommendation, the primary use of gene silencers is worthwhile particularly in aggressive disease. It is important to perform genetic testing of potential carriers of mutations (eMethods) and to initiate treatment as soon as the first manifestations are noted. The mean annual cost of treatment is around € 160 000 for tafamidis, € 320 000 for inotersen, and € 360 000 for patisiran. In-label use in Germany is covered by health insurance.

Wild-type ATTR amyloidosis

No substance is yet approved for the treatment of ATTRwt amyloidosis. The efficacy of tafamidis against cardiac ATTRwt amyloidosis has been demonstrated (36). Licensing in Germany is anticipated, but until that time only off-label use is possible.

Key messages

Conflict of interest statement
Dr. Ihne’s research was supported by the Comprehensive Heart Failure Center (CHFC) Würzburg and the Interdisciplinary Center of Clinical Research (IZKF), Würzburg. She has received funding for a project of her own initiation from Akcea; consultancy and lecture fees from Takeda, Pfizer, Janssen, and Akcea; and reimbursement of congress registration fees as well as travel and accommodation costs from Takeda, Pfizer, Akcea, and Alnylam. An internship abroad was supported by ONLUS.

Dr. Morbach carries out her research in the framework of a cooperation agreement between Tomtec Imaging Systems and the University of Würzburg, supported by the Bavarian Digital Master Plan II. Furthermore, she is a member of the patient selection board of EBR Systems and has participated in the advisory boards of Akcea, Alnylam, and Pfizer. She has received funds to support congress travel costs from Orion Pharma and Alnylam and lecture fees from Alnylam.

Prof. Sommer is a member of the advisory boards of Akcea, Alnylam, and Pfizer. She has received payments for the preparation of scientific meetings from Alnylam and Pfizer, and has received funding for a project of her own initiation from Pfizer.

Prof. Knop is a member of the advisory boards of Celgene, Amgen, Bristol-Myers Squibb, and Molecular Partners.

Prof. Störk is supported by the CHFC Würzburg, and by the German Federal Ministry of Education and Research (BMBF). He has received consultancy and lecture fees as well as reimbursement of travel costs from AstraZeneca, Bayer, Boehringer Ingelheim, Novartis, Pfizer, and Servier.

Prof. Geier is a member of the steering committees of Gilead, Intercept, and Novartis. He receives consultancy fees from AbbVie, Alexion, BMS, Gilead, Intercept, Ipsen, Novartis, Pfizer, and Sequana, and has received lecture fees from AbbVie, Alexion, BMS, CSL Behring, Falk, Gilead, Intercept, Merz, Novartis, and Sequana.

Manuscript received on 25 August 2019, revised version accepted on 12 December 2019

Translated from the original German by David Roseveare

Corresponding author
Prof. Dr. med. Stefan Störk, PhD

Interdisziplinäres Amyloidosezentrum Nordbayern,
Deutsches Zentrum für Herzinsuffizienz (DZHI), Universitätsklinikum Würzburg

Am Schwarzenberg 15, Haus A15

97078 Würzburg, Germany

Cite this as
Ihne S, Morbach C, Sommer C, Geier A, Knop S, Störk S:
Amyloidosis—the diagnosis and treatment of an underdiagnosed disease.
Dtsch Arztebl Int 2020; 117: 159–66. DOI: 10.3238/arztebl.2020.0159

►Supplementary material

For eReferences please refer to:
www.aerzteblatt-international.de/ref1020

eMethods, eBox, eTable:
www.aerzteblatt-international.de/20m0159

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