Chapter 108: Immunoglobulin Light-Chain Amyloidosis

Amyloidosis is a heterogeneous group of diseases characterized by tissue infiltration with misfolded protein precursors as amyloid material. For nearly 100 years, amyloid has been defined by its staining properties. Divry and Florkin first used Congo red to detect amyloid in the brain of patients with Alzheimer disease.¹ Amyloid deposits are always extracellular and, under the light microscope, appear amorphous and pink when seen after standard hematoxylin-and-eosin staining. All amyloid deposits bind Congo red dye and demonstrate green birefringence under polarized light,² and this test remains the standard diagnostic procedure required to confirm a diagnosis of amyloidosis. Under the electron microscope, amyloid consists of rigid, linear, nonbranching fibrils of 9.5 nm diameter.³ Historically, amyloid was defined based on whether there was a family history (inherited), whether it was the result of a chronic inflammatory condition (secondary), or whether it was idiopathic (primary). Today, amyloidosis is classified based on the protein subunit composition of the deposits. The term “primary amyloid” is archaic and should not be used. Instead, such cases should be called “immunoglobulin light-chain (AL) amyloidosis,” reflecting the fact that they represent a systemic plasma cell dyscrasia. The subunit classification is important because AA amyloidosis (secondary) can be the consequence of sustained inflammation but can also be inherited, as in familial Mediterranean fever. Inherited forms of amyloidosis are generally composed of mutant transthyretin (TTR) but can also be a consequence of mutations in apolipoprotein, fibrinogen, and gelsolin.⁴ Senile systemic amyloidosis, primarily a cardiac disorder, is being increasingly recognized, and is caused by deposition of wild-type TTR as amyloid material in patients older than age 60 years.⁵ Table 108–1 lists the nomenclature of the various forms of amyloidosis. Practicing hematologists and oncologists are not likely to see patients with forms of amyloidosis other than immunoglobulin light-chain (AL) amyloidosis. This is the only form that is responsive to chemotherapy and is the focus of this chapter; additionally, the term amyloidosis, unless specified otherwise, refers to AL amyloidosis.

Amyloidosis is rare, with an incidence of eight per million persons per year with a median age at diagnosis of 67 years.¹¹ This makes it one-sixth as common as myeloma and twice as common as Waldenström macroglobulinemia. Conversely, a practicing oncologist should see approximately one light-chain amyloid patient for every six patients with myeloma in the oncologist’s practice. If this is not the case, there is a significant likelihood that the disease is going unrecognized.

The fibrils of immunoglobulin light chain amyloid are composed, in most patients, of fragments of immunoglobulin light chains. A normal immunoglobulin light chain has a molecular weight of approximately 25 kDa, but the immunoglobulin light chains found in amyloid deposits usually range from 8 kDa to 15 kDa. The fragment size is important because it usually reflects the deletion of the constant region of the immunoglobulin light chain, making immunohistochemistry a poor technique to identify the fibril type in paraffin-embedded tissues.⁶ A fraction of patients have immunoglobulin heavy chain amyloid deposits where fragments of immunoglobulin G, A, or M heavy chains comprise the basic subunit. Whereas AL amyloidosis represents approximately 62 percent of all amyloid patients, immunoglobulin heavy-chain amyloidosis represents less than 1 percent of all patients.⁷

There is clearly something “amyloidogenic” about the immunoglobulin light chains in patients with AL amyloidosis. Unlike monoclonal gammopathy and myeloma where the κ:λ ratio is 2:1, in AL amyloidosis, the κ:λ ratio is 1:3, suggesting an intrinsic propensity of λ light chains to form amyloid. Moreover, the subgroup λ_VI is exclusively found in patients with AL amyloidosis.⁸ When the light chains are extracted from the urine of patients with myeloma and injected into mice, amyloid deposits are not seen. However, when the light chains from patients with amyloidosis are extracted from the urine and injected into mice, they will develop amyloidosis.⁸ The exact structural characteristics that lead to the misfolding of the α helical protein into the amyloid β-pleated sheet configuration are unknown. Patients with amyloidosis are classified into those with myeloma and those without myeloma. The percentage of plasma cells present in the marrow at the time of diagnosis is prognostic and predicts outcome in patients with amyloidosis.⁹ As a result, the percentage of plasma cells in the marrow may dictate alternate therapeutic considerations at diagnosis (see “Therapy” below). Overt myeloma with CRAB criteria (hypercalcemia, renal insufficiency, anemia, or bone disease) is uncommon in AL amyloidosis. However, an elevation in the percentage of plasma cells in the marrow of patients without CRAB criteria confers the same adverse prognosis as observed in patients who have overt symptomatic myeloma, and these groups can be considered as a single cohort of myeloma-associated amyloidosis. Patients who do not have myeloma at presentation have almost no chance of developing myeloma later in the course of their disease.¹⁰ The plasma cells in the marrow of patients with amyloidosis tend to be nonproliferative and frequently lack the karyotypic abnormalities typically seen in myeloma, such as –17p, t(4;14), and –13. A translocation 11;14 is commonly seen in amyloidosis and appears to confer an inferior outcome. Circulating plasma cells detectable by flow cytometry are uncommonly seen relative to their frequency in myeloma¹²

Unfortunately, the symptoms of amyloidosis are vague and often nonspecific. Physical findings, when present, can be highly specific but are only present in a minority of patients. For a disease this rare, it is important for clinicians to have an operational approach to avoid inappropriate resource utilization. Only 1 percent of patients with AL amyloidosis are younger than age 40 years. Consequently, it would be unlikely for younger patients to have AL amyloidosis, although this age group regularly can be seen with secondary systemic amyloidosis. The majority of patients with AL amyloidosis are males (66 percent), unlike myeloma, where the male-to-female is 52:48.¹⁵

The most common symptoms reported by patients with amyloidosis are fatigue, weight loss, and lower-extremity edema. Unfortunately, these symptoms are too nonspecific to be used as a trigger to screen patients, as the yield for these vague symptoms would be very low. The mechanism underlying fatigue in this disorder is usually amyloid heart disease, which can be an extremely subtle diagnosis and is discussed further under the specific amyloid syndromes. Weight loss accompanying amyloidosis can be impressive, and may exceed 20 kg. This usually results in an investigation for occult malignancy; but even if blind biopsies are performed, the diagnosis may be overlooked if a specific request for amyloid stains is not made to the pathologist. Lower-extremity edema may be attributable to nephrotic range proteinuria, hypoalbuminemia, and transudation of serum into the extracellular space. Edema may also be seen from high filling pressures caused by the restrictive cardiomyopathy, which, again, can easily be overlooked because of the subtle diagnostic testing required. These patients are often treated empirically with diuretics until cardiac dysfunction becomes more evident.

The physical findings of amyloidosis are present in only one patient in six. Periorbital purpura is frequently cited as a diagnostic finding and, when present, is useful but is only seen in 15 percent of patients (Fig. 108–1). Sometimes, the purpura is subtle and can only be seen with the patient’s eyes closed. Even when purpura is present, it may lead to an evaluation of a coagulopathy or platelet dysfunction, which would invariably be negative in this setting. Purpura not only is seen on the eyelids but also on the face, neck, and anterior chest above the nipple line. Enlargement of the tongue is seen in approximately one person in eight (Fig. 108–2). Dental indentations on the underside of the tongue are characteristic. Often the patient will have sudden-onset of sleep apnea syndrome as a result of occlusion of the airway by the enlarged tongue when the patient is supine.¹⁶ Even when diagnostic findings are present, their significance is often missed, leading in many cases to tongue biopsy with a preoperative suspicion of tongue cancer. Most patients with enlargement of the tongue will also have palpable submandibular lymphadenopathy, usually caused by displacement of the nodes by the enlarged base of the tongue; although amyloid infiltration of the submandibular gland may also result in a firm palpable mass in the submandibular region. Hepatomegaly is seen in approximately 20 percent of patients and may be due to direct infiltration of the liver, which will cause a firm markedly enlarged liver.¹⁷ In some patients, however, the liver enlargement is a reflection of high venous filling pressures in the right-sided cardiac chambers and represents chronic passive congestion. Patients rarely have periarticular infiltration of the shoulders producing the so-called shoulder pad sign, a baseball-shaped enlargement of the anterior soft tissues of the shoulder. A rare patient will develop temporal artery infiltration and develop classic jaw claudication, as well as limb, buttock, and calf claudication.¹⁸ On questioning, many patients will have xerostomia from infiltration of the minor salivary glands; and at some centers, biopsy of the minor salivary glands is a preferred technique for the diagnosis of amyloidosis.¹⁹

Because the symptoms of amyloidosis are highly nonspecific and the physical findings are specific but not very sensitive, an operational approach is required to ascertain which patients need investigation for amyloidosis. We recommend screening for AL amyloidosis when a patient is seen with any of the following clinical syndromes:

• Nephrotic range proteinuria with any serum creatinine level

• Infiltrative cardiomyopathy or heart failure with preserved ejection fraction. A normal ejection fraction does not exclude AL amyloidosis

• Hepatomegaly or alkaline phosphatase elevation without specific imaging abnormalities

• A mixed axonal demyelinating peripheral sensory, motor or autonomic neuropathy, particularly when associated with a monoclonal gammopathy

• A patient with myeloma with symptoms that are not typical of the disease, particularly profound, unexplained fatigue

Table 108–2 gives the frequency of amyloid syndromes seen in patients at the Mayo Clinic. If an oncologist sees a patient with one of these five syndromes, or an internist is faced with an undiagnosed patient, laboratory evaluation is indicated, as outlined below.

LABORATORY FEATURES

The best screening tests for initial evaluation of patients with suspected amyloidosis are immunoelectrophoresis and immunofixation of both serum and urine and a serum immunoglobulin free light-chain assay (both κ and λ). Systemic immunoglobulin AL amyloidosis is a plasma cell dyscrasia, and 99 percent of patients will have a detectable abnormality of one of these three tests, reflecting synthesis by a clonal population of plasma cells in the marrow. If an immunoglobulin protein is detected, further investigation for amyloidosis as described in the next section (“Differential Diagnosis”) should proceed. If a systemic plasma cell dyscrasia and an immunoglobulin light chain cannot be confirmed, three possibilities exist: (1) the patient does not have amyloidosis, (2) the patient does not have systemic amyloidosis, or (3) the amyloidosis is not immunoglobulin light chain in type and reflects a different protein subunit.

The serum free light-chain assay is a critically important test. It not only heightens the suspicion of the presence of immunoglobulin AL amyloidosis, it also is prognostic and vital to staging the patient. The serum immunoglobulin free light chain is part of the response evaluation for this disease. A screening serum protein electrophoresis is insufficient as a screening technique because a visible M-spike is seen in less than half of patients because of the high prevalence of primary light-chain proteinemia.

Finding a monoclonal protein in the serum or in the urine of a patient with heavy albuminuria often obviates the need for a renal biopsy. A patient with free light chains in the serum or urine and proteinuria can have only one of three disorders: (1) myeloma cast nephropathy, (2) AL amyloidosis, or (3) Randall-type immunoglobulin deposition disease (κ).

Screening for a light-chain immunoglobulin is the best noninvasive approach when confronted with a patient with any of the five syndromes listed in Table 108–2. If amyloid is present but the light chains are normal, strong consideration of referral to a specialty center to further clarify the underlying form of amyloidosis should be considered.

DIFFERENTIAL DIAGNOSIS

Once a clinician has begun an evaluation of a patient with a compatible clinical syndrome and an immunoglobulin abnormality has been detected, a biopsy is required to confirm the diagnosis before therapy should commence. Although imaging of amyloid deposits with various radionuclides, most notably anti–serum amyloid P component, continue to be explored and used in practice, they are not a substitute for histologic confirmation of the presence of amyloidosis.^20,21,22 In a patient with renal, cardiac, hepatic, or peripheral nerve amyloidosis, it is straight forward to establish the diagnosis by kidney, heart, liver, or nerve biopsy, but this is unnecessary in the majority of patients. Subcutaneous fat aspiration is a bedside office procedure done with local anesthesia and does not require an incision (Fig. 108–3). An excellent YouTube video has been produced by the Boston Medical Center on the technique (https://www.youtube.com/watch?v=tctYTmxd9gQ). Typically, fat aspirations are reviewed at a specialty center unless the pathology department regularly processes fatty tissue. The fat is not paraffin-embedded and, therefore, it is subject to overfixation, trapping of Congo red dye, and the possibility of inadequate controls.²³ Fat aspiration is positive in three-quarters of patients with amyloidosis.

A second tissue easily stained for amyloid is the marrow. Because AL amyloidosis patients will have a plasma cell dyscrasia, a marrow examination is clinically indicated to quantify the number of plasma cells in the marrow. Congo red staining of marrow blood vessels can detect amyloid deposits in half of patients with AL amyloidosis. Combining the two techniques (marrow and fat pad aspiration), establishes a diagnosis in 85 percent of afflicted patients. Minor salivary gland biopsy, endoscopic gastric biopsy, rectal biopsy, and skin biopsy can also be used to establish the diagnosis. If the clinical suspicion of AL amyloidosis is strong and these biopsies are negative, it is appropriate to biopsy the affected organ.

Once tissue containing Congo red has been identified, it becomes imperative that the protein subunit be determined. Historically, immunohistochemistry has been used to identify the type of amyloid, but immunohistochemistry can be challenging because only those protein subunits for which antisera exist can be detected.^24,25 Second, particularly in AL amyloidosis, the reactive epitope may have been deleted during the process of amyloid fibril formation and, frequently, the background staining is high, particularly in kidney tissues. Third, because the protein in amyloid misfolds, even if the epitopes are present, they may be hidden deep within the deposits and may be inaccessible to commercial antisera. Not only can immunohistochemistry be unreliable, it can be misleading. It is therefore recommended that laser capture of the amyloid deposit be performed routinely followed by mass spectroscopic analysis.^26,27,28 The subunit protein can be identified by this approach in the majority of cases. Even in patients who have a false-positive Congo red stain, this technique is useful because it will not identify amyloid-related peptides upon analysis. With this technique, one is able to confirm the presence of AL amyloidosis, which represents slightly less than two-thirds of patients seen with amyloidosis. A full quarter of patients with amyloid deposits are composed of amyloidogenic transthyretin (ATTR) (inherited) or wild-type amyloid (senile systemic). Less than 4 percent are amyloid A (AA) and approximately 4 percent represent ALect2 amyloidosis, which deposits in the kidney and causes proteinuria. Other forms of amyloid, which are often localized, are seen in less than 1 percent of patients. A particularly important form of localized amyloid occurs at the sites of subcutaneous insulin injections in diabetics. Crystalline insulin can form amyloid, which can cause discolored firm deposits which, when biopsied, will be Congo red–positive, but by mass spectroscopic analysis, can be confirmed to be insulin. Other forms of systemic amyloidosis for which systemic chemotherapy is contraindicated include fibrinogen A-α amyloidosis, and amyloid caused by apolipoprotein-A1, and gelsolin.

One additional advantage, particularly for those patients who have TTR amyloidosis is that mass spectroscopy not only identifies the protein, in most instances, it can confirm whether the protein is wild-type or a mutant. We still recommend that patients who have mutant TTR seen on mass spectroscopy have this confirmed by DNA sequencing of a blood sample, which is a readily available commercial test, to confirm the findings on mass spectroscopy. We have investigated a small number of patients in whom an amyloid syndrome was strongly suspected, a subcutaneous fat aspirate was not definitively positive, yet mass spectroscopic analysis demonstrated peptides in the tissue that are associated with amyloid including apolipoprotein-E and serum amyloid P component. When a pathologist makes a diagnosis of amyloid in tissue sections, the clinicians are required to ask what type of amyloidosis it represents. Although not widely available, mass spectroscopic analysis is the most sensitive and specific technique for identifying the amyloid subunit protein.

DIAGNOSIS AND CLINICAL CHARACTERIZATION OF ORGAN-SPECIFIC SYNDROMES

Kidney

Kidney involvement is seen in 45 percent of patients with immunoglobulin AL amyloidosis. It is conspicuously absent in the majority of patients with TTR amyloidosis until late in the disease. Renal involvement is virtually universal in systemic AA amyloidosis as well as ALect2 amyloidosis and A-fib α amyloidosis. Amyloid is seen in 2.5 percent of all renal biopsies. When limited to nondiabetics older than age 50 years, amyloid deposits will be found in 10 percent of renal biopsies.²⁹ These patients present with the typical four features of the nephrotic syndrome: (1) nephrotic range proteinuria, (2) hypoalbuminemia, (3) hyperlipidemia, and (4) edema. Nearly a third of patients with renal amyloidosis have at least a 1-year history of dramatic elevations of cholesterol and triglycerides. These are often managed with statin-type medication and dietary modification without consideration that a dramatic (>100 mg/dL) rise in cholesterol and triglycerides may be caused by heavy proteinuria. In the majority of patients, the glomerular filtration rate (GFR) is preserved until sustained proteinuria has been present for years. Only a small percentage of patients, usually with interstitial but not glomerular amyloid, present with renal insufficiency in the absence of heavy proteinuria.³⁰

The management of the lower-extremity edema is primarily diuretic therapy. However, excessive diuretic use, particularly in patients with cardiac amyloidosis, can aggravate already reduced intravascular volume. Diuretics can also compromise renal blood flow, increase orthostatic hypotension, and reduce cardiac filling pressures necessary for adequate cardiac output in patients that have “stiff heart syndrome.” The threat of continuous proteinuria in amyloidosis is damage to the tubular system. One-third of patients with renal amyloidosis will ultimately require dialysis or renal transplantation.³¹ The serum creatinine level at the time of presentation is the best predictor of which patients are most likely to require dialysis. Clearly, the best method for prevention of the need for dialysis is effective therapy of the underlying plasma cell dyscrasia. There are no reported differences between outcomes for those patients receiving hemodialysis and those receiving peritoneal dialysis.

In rare instances, patients have profound depression of the serum albumin below 1 g/dL. These patients often will be disabled by anasarca. In situations where intractable edema and anasarca makes management next to impossible, renal ablation has been performed to stop the urinary protein leak, normalize the serum oncotic pressure, and resolve the edema. Multiple techniques have been reported, including nephrectomy, ligation of the renal artery, and bilateral ureteral clips. In some patients, the early initiation of dialysis, even with a normal estimated GFR, can result in anuria and restoration of normal serum albumin levels.³²

The correlation between the amount of amyloid detected and the degree of renal dysfunction is poor. The urinary sediment is nonspecific, shows fat and fatty casts, but generally does not contain red cell casts. The most common cause of death in patients with renal amyloidosis is progressive cardiac dysfunction from infiltrative amyloid cardiomyopathy.

Heart

Unlike most cardiac disorders, which are caused by a loss of systolic function, the restrictive cardiomyopathy caused by amyloid infiltration results in poor relaxation (so-called stiff heart syndrome) and poor filling during diastole so that the ventricular chamber has a low end-diastolic volume, which results in reduced stroke volume and a reduced cardiac output. This constitutes a classic example of heart failure with preserved systolic function. In fact, the majority of patients with amyloidosis have an echocardiographically normal ejection fraction until late in the disease.⁵ Cardiac amyloid is found in 40 to 50 percent of patients at diagnosis and is responsible for nearly 90 percent of deaths. It is the most challenging syndrome to diagnose because of the lack of specificity of its symptoms. Fatigue and dyspnea on exertion are often not associated with cardiac disease in the presence of amyloid (1) because of the lack of radiographic changes of cardiomegaly, pleural effusions, and pulmonary vascular redistribution; (2) because echocardiography will demonstrate preserved ejection fraction; and (3) because coronary angiography is invariably normal.³³ This triad often leads to a diagnosis of noncardiac dyspnea. Even when amyloid infiltrates the myocardial wall and causes it to be thickened, it is often misattributed to hypertensive heart disease (hypertrophy) rather than infiltration (Fig. 108–4). Electrocardiographic abnormalities, including pseudoinfarction and low voltage, are quite common but are frequently overlooked, whereas a pseudoinfarction pattern is misattributed to ischemic heart disease.

The supportive care of patients with cardiac amyloidosis can be strikingly different from that of ischemic or valvular heart disease. There is no evidence that afterload reduction with angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers benefits patients with relaxation abnormalities, and dyspnea and reduced exercise tolerance frequently increase in patients treated with these medications. Fatigue and dyspnea on exertion can also be exacerbated when β blockers are used for rate or rhythm control.

In addition to standard echocardiography, accurate diagnosis of cardiac amyloid requires Doppler flow studies to demonstrate the rapid decline in velocity of blood inflow into the ventricular chambers and optimally conducted cardiac strain studies that demonstrate a decline in the rate of fractional shortening of the ventricular chamber. Patients with unexplained fatigue and/or dyspnea on exertion should have immunofixation of the serum and urine and free light-chain testing to assess for possible light-chain amyloid. However, even if light chain-testing is negative, age related amyloidosis may still be present because of the deposition of wild-type TTR in the heart.³⁴ This typically occurs in patients older than age 60 years, predominantly men, half of whom will also have carpal tunnel syndrome.^35,36 Wild-type TTR amyloidosis will not be detected by screening for serum and urine light chains, and subcutaneous fat aspiration has a lower sensitivity than in AL amyloidosis. These patients require recognition by echocardiography, magnetic resonance imaging (MRI), or endomyocardial biopsy to establish a diagnosis (Fig. 108-5).

Early diagnosis of cardiac amyloid is imperative because it is this group that is responsible for the majority of the early deaths with this disorder. In our experience, 40 percent of newly diagnosed patients with AL amyloidosis will succumb to the disease within the first year; and this percentage has not changed over a quarter century.

Echocardiography remains the most useful test for the imaging and diagnosis of amyloid; however, it is not particularly useful for serial monitoring of patients for response or progression after treatment. The technique still suffers from interobserver variability, and the calculations of the septal thickness can vary substantially on serial measurements. Conversely, a septal thickness greater than 15 mm would be rare with hypertensive cardiomyopathy and would be limited to either amyloidosis or hypertrophic cardiomyopathy. Interestingly, the degree of cardiac infiltration in senile systemic and familial amyloid cardiomyopathy is substantially greater than that seen in AL amyloidosis. A patient with AL amyloidosis with a septal thickness greater than 18 mm will generally have significant disability related to cardiac failure. Patients with TTR amyloidosis, both mutant and wild-type, will frequently have septal thicknesses in the range of 25 mm with minimal symptomatology. The old echocardiographic finding of granular sparkling appearance is little used today. Other echocardiographic clues include thickening of the right ventricle and reduction in left ventricular chamber size.³⁷ Late consequences of cardiac involvement include valvular thickening and valvular regurgitation. Repair of the valve will not result in meaningful improvement in the patient’s aerobic exercise capacity. The restriction to flow seen in restrictive cardiomyopathy can be confused with restrictive pericardial disease; and occasionally, patients have undergone pericardiectomies without benefit.³⁸ Endomyocardial biopsy is highly sensitive in the diagnosis of cardiac amyloidosis; and if five specimens are taken, recognition of the diagnosis is virtually certain. Patients with cardiac amyloidosis have poor atrial function and a high incidence of atrial standstill. Atrial and atrial appendage thrombi are well recognized and are potential sources of cardiac embolism.³⁹ Rare patients can develop amyloid deposition in the coronary microcirculation resulting in true ischemic symptomatology and angina with normal epicardial coronary artery anatomy.⁴⁰

Sudden death remains a problem in patients with amyloidosis.⁴¹ The placement of an implantable defibrillator may not reduce the risk of sudden death.⁴² Electromechanical dissociation is a common occurrence and the ability of a fibrillating amyloid heart to be appropriately shocked internally and establish hemodynamic stability has not been established.⁴³

Diuretic therapy remains the mainstay of management for cardiac amyloidosis; but in these patients with noncompliant ventricular chambers, higher than normal filling pressures are often required to open the ventricle and fill it with blood. Aggressive diuretic therapy will often reduce preload, and this can result in drops in systolic blood pressure, reduced renal blood flow, and syncope.⁴⁴

Familial amyloid cardiomyopathy is rare, but one special TTR mutant known as TTRVal122Ile requires awareness. In a prospective study of cord blood samples, this mutation was found in 3 percent of newborns of American parents of African descent. This compared with a prevalence of 0.44 percent in Americans of European descent and 0 percent of Americans of Hispanic descent. The degree of penetrance of this mutation at the clinical level has not been determined; however, in view of the high incidence and prevalence of this genetic abnormality, the diagnosis of cardiac amyloidosis in Americans of African descent warrants early analysis of the DNA for this mutation.^45,46

Cardiac biomarkers play an important role in the prognosis of amyloid as well as in its functional assessment.⁴⁷ Both the B-natriuretic peptide and troponin levels predict outcomes in patients with amyloidosis and are important parts of the staging system for this disease.⁴⁸ Staging involves assigning a point for any of the following characteristics: difference between the involved and uninvolved free light chain of greater than 180 mg/L; for a cardiac troponin T level greater than 0.025 ng/mL; and for the N-terminal of the prohormone brain natriuretic peptide (NT-proBNP) level greater than 1800 pg/mL. This creates four stages with median survivals ranging from 6 months (stage 4) to 60 months (stage 1). Serialized measurements of the NT-proBNP also have been used to define response and progression and, in fact, have supplanted the use of serial echocardiography to assess changes over time, both in following the natural history as well as assessing response to therapeutic interventions.^49,50,51 All patients who present with amyloidosis, whether or not cardiac disease is suspected, should have cardiac biomarkers performed. Table 108–3 lists the suggested diagnostic tests to perform when a patient with amyloidosis is seen.

Contrast-enhanced cardiac MRI is increasingly being used in the assessment of cardiac amyloid. Cardiac MRI (Fig. 108–6) can measure the thickness of the myocardium accurately and, after gadolinium injection, can demonstrate delayed subendocardial enhancement that can be quite specific for cardiac amyloidosis.^52,53 Phase-contrast MRI provides information on flow dynamics, diastolic filling parameters, and mitral peak in-flow velocity.⁵⁴ By providing a functional assessment, this technique can help establish an early diagnosis and has the potential to assess response to therapy. MRI cannot be used in the presence of a pacemaker or defibrillator or if there is renal insufficiency, because gadolinium is contraindicated. Radionuclide scanning is being explored for amyloidosis. Technetium pyrophosphate is a sensitive marker for the presence of ATTR amyloidosis, both wild-type and mutant, whereas uptake is not seen in AL amyloidosis.⁵⁵ A recent small study assessing ¹¹C-labeled Pittsburgh Compound-B (¹¹C-PiB)–based positron emission tomography (PET) imaging identified cardiac amyloid deposits in all patients with light chain amyloidosis and ATTR and was negative in controls.⁵⁶ Therefore, nuclear imaging in the future may not only help confirm cardiac involvement by amyloidosis, but also help differentiate one type versus another.

Liver

Liver infiltration from amyloid can be seen in up to one-quarter of patients with AL amyloidosis.¹⁷ These patients will present with hepatomegaly, elevation of the serum alkaline phosphatase with normal or near-normal transaminases and bilirubin. Half of the patients with hepatic amyloidosis have renal amyloidosis, which dominates the clinical syndrome. When a patient presents with hepatomegaly and imaging shows no filling defects, the presence of proteinuria, a monoclonal protein, or the presence of Howell–Jolly bodies in a blood film indicative of hyposplenism are highly suggestive of amyloidosis. Most patients have symptoms consistent with chronic liver disease, early satiety, anorexia, and unexplained weight loss. It is common to find spider telangiectasias on the upper chest. Portal hypertension and ascites are uncommon, however.⁵⁷ Rare instances of both hepatic and splenic rupture have been reported.⁵⁸ The diagnosis can usually be established with fat aspiration and marrow biopsy, but a liver biopsy is safe and does not have a higher risk of bleeding complications than in other patients with liver disease.

Nervous System

Amyloid, by virtue of its deposition in the vasa nervorum, causes a mixed axonal and demyelinating peripheral neuropathy. The neuropathy is symmetric, tends to ascend beginning in the toes, and eventually involves the upper extremities. It causes paresthesias, often painful dysesthesias, and eventually causes motor loss. Approximately half of the patients have an associated carpal tunnel syndrome, and approximately one-quarter have associated autonomic features including orthostatic hypotension, autonomic dysmotility of the gastrointestinal tract, including vomiting because of pseudoobstruction and alternating constipation with diarrhea, often intractable, and bladder abnormalities, including overflow incontinence and incomplete emptying.^59,60 The progression of amyloid neuropathy is slow, and it is common to have delays of 2 to 3 years before a diagnosis is established. Electromyography is not particularly useful in the early diagnosis because amyloid preferentially affects the small unmyelinated fibers of the extremities, which are not well assessed with standard electrodiagnostic studies. Patients with an unexplained peripheral neuropathy who are not diabetic should have immunofixation of serum and urine and a free light-chain assay performed. A positive finding requires the consideration of amyloidosis in the differential; although, for patients who have an immunoglobulin (Ig) M monoclonal protein, the possibility that the IgM is directly responsible for neuropathy in the absence of amyloid is significant. Sural nerve biopsies can usually detect the amyloid deposits, but there are reports in the literature of sural nerve biopsies having missed proven amyloidosis.⁶¹ Mass spectroscopic analysis of the amyloid deposits is particularly important because of the high prevalence of neuropathy in patients with non-AL amyloidosis.

Treatment of amyloidosis has improved significantly with the introduction of novel agents and refinements in autologous stem cell transplantation. For years, the regimen of melphalan and prednisone was the standard of therapy, but the response rate never exceeded 25 percent, and the impact on survival was unimpressive. Melphalan and prednisone therapy has now been supplanted by the use of melphalan and dexamethasone, which has a very low therapy-related mortality and can be administered to patients with cardiac and renal failure as well as frail patients. The 5-year actuarial survival in patients treated with melphalan and dexamethasone is 50 percent but is highly dependent on the enrolled population. Median responses as short as 10.5 and 17.5 months have been reported and are a function of the proportion of patients with advanced cardiac amyloid enrolled. Retreatment with melphalan and dexamethasone after an initial response also can be successful. It is often difficult to interpret results in phase 2 trials because of patient heterogeneity. Stratification of patients, based on the staging mentioned above, is important in reporting outcomes. Melphalan and dexamethasone should be considered the standard of care in patients that are not eligible for stem cell transplantation.⁶⁶

AUTOLOGOUS STEM CELL TRANSPLANT

Most experts believe that autologous stem cell transplantation is the treatment of choice for patients with amyloidosis who do not have severe end-organ dysfunction, even though this approach has not been proven superior to conventional chemotherapy in prospective randomized trials or meta-analyses. However, it must be recognized that no more than 20 percent of patients with amyloidosis are eligible for stem cell transplantation. Currently, the therapy-related mortality at the Mayo Clinic is 2.5 percent (three out of 120), and the 10-year overall survival is 43 percent. Significant improvements in organ function and quality of life are commonly observed following stem cell transplantation and are strongly correlated with attainment of a very good partial response or better.^67,68,69 To reduce treatment-related mortality, current patient selection for transplantation includes age younger than 70 years, serum creatinine less than 1.8 mg/dL, serum troponin T less than 0.06, and an NT-proBNP less than 5000 pg/mL. The median age at the time of transplantation at the Mayo Clinic is 57 years. The median percent plasma cells in the marrow of transplanted patients is 7 percent, and the median urinary protein loss is just under 4 g/day. Seventy percent of patients who receive autologous stem cell transplantation have predominant renal involvement, 12 percent have peripheral neuropathy, and 14 percent have liver involvement. Patients with advanced cardiac involvement are generally excluded from transplantation, although half of transplanted patients have mild to moderate cardiac involvement as assessed by biomarkers and echocardiogram.

Blood stem cells are generally mobilized using leukocyte growth factors alone without cytotoxic chemotherapy to avoid hemodynamic deterioration during the mobilization process. A median of two aphereses are required to collect adequate stem cells for transplantation. The standard conditioning regimen is melphalan 200 mg/m², although the dose may be reduced for multiorgan involvement, age, and frailty. Induction chemotherapy is not generally administered prior to autologous stem cell transplantation, although this approach is considered in patients with significant marrow plasmacytosis, because of data suggesting an inferior outcome in such patients. In 2013, 40 percent of patients were transplanted at the Mayo Clinic without requiring hospitalization, and of the 60 percent of patients who were hospitalized, the median hospital stay was 6 days. Leukocyte growth factors are not routinely used after transplantation because they increase fluid retention. A partial response or better is seen in 75 percent of patients. Complete hematologic responses are documented in 40 percent of patients. Organ responses are seen in 50 percent of patients transplanted at the Mayo Clinic. Median survival for complete responders has not been reached, whereas patients with partial response or better have a median survival of 107 months. Predictors of outcome following autologous stem cell transplantation include cardiac biomarkers, NT-proBNP, and troponin.⁷⁰

IMMUNOMODULATORY DRUGS

The combination of melphalan, dexamethasone, and lenalidomide has been reported for the treatment of AL amyloidosis. The maximum tolerated dose of lenalidomide was found to be 15 mg. Melphalan doses lower than those recommended for myeloma patients are used (0.18 mg/kg/day for 4 days every 28 days), with a complete response rate of 42 percent, an overall response rate of 58 percent, and a 2-year overall survival of 81 percent. Prophylaxis against deep venous thrombosis is required when lenalidomide is used. A combination of cyclophosphamide, thalidomide, and dexamethasone is safe and effective. In a risk-adapted all-oral therapy, 75 patients (with PS was 0-1) were treated, with a hematologic response in 74 percent, of which 21 percent were complete. The 3-year estimated overall survival was 82 percent, and grade 2 toxicity was seen in 52 percent. Lenalidomide and dexamethasone have been used in amyloidosis in a fashion identical to that used for multiple myeloma. It is important to remember that lenalidomide can increase the level of NT-proBNP and may actually aggravate heart failure.⁷¹ Additionally, the typical dose of lenalidomide used to treat multiple myeloma is not well tolerated by AL patients and treatment should be initiated at a dose of no more than 15 mg daily. There is a high discontinuation rate of lenalidomide within the first three cycles. Myelosuppression, skin rash, and fatigue are common. In a study of lenalidomide and dexamethasone in patients who had failed melphalan and bortezomib, two patients died prior to first-response evaluation and 50 percent experienced grade 3 or greater toxicity. The hematologic response rate was 41 percent. The median overall survival was 14 months. Cyclophosphamide, lenalidomide, and dexamethasone have been used in the treatment of amyloidosis with lenalidomide at 15 mg per day and cyclophosphamide 100 mg per day. A partial response or greater was observed in 55 percent of patients, with complete responses in 8 percent, organ responses in 40 percent, and a 2-year overall survival of 41 percent. Cyclophosphamide, lenalidomide, and dexamethasone hematologic response rates ranged from 40 to 77 percent in three different studies. Complete responses did not exceed 10 percent. Lenalidomide toxicity was substantial and included fatigue and fluid retention.

Pomalidomide has been used with dexamethasone in relapsed amyloidosis. In a population of 33 evaluable patients, the response rate was 48 percent with a median time to response of 2 months. Organ improvement was found in 15 percent. The progression-free survival was 14 months; overall survival was 28 months.⁷²

Bortezomib is highly active in the treatment of amyloidosis.⁷³ The combination with dexamethasone in untreated patients produces a 47 percent complete response rate, with higher responses seen in patients treated with twice-weekly bortezomib. The cardiac response rate is 29 percent. Hematologic responses are associated with cardiac response as measured by a reduction in NT-proBNP. Bortezomib also has been used with melphalan and dexamethasone, as well as cyclophosphamide with dexamethasone.⁷⁴ The CyBorD (cyclophosphamide, bortezomib, and dexamethasone) regimen was reported by the Mayo Clinic as a retrospective review of 17 patients with responses seen in 94 percent (71 percent complete, 24 percent partial) and a median time to response of 2 months.⁷⁵ In many published trials, patients with severe cardiac involvement were excluded; as a consequence, it is difficult to determine the efficacy of bortezomib in this difficult subgroup.⁷⁶ In one study of 38 patients with advanced cardiac disease using reduced doses of twice-weekly bortezomib and dexamethasone, 18 of 38 patients died during therapy; 21 patients achieved a hematologic response after a median of three cycles. In a series of 35 patients treated with bortezomib-dexamethasone with subsequent addition of cyclophosphamide, 86 percent achieved a rapid response. A second trial of cyclophosphamide-bortezomib-dexamethasone resulted in hematologic responses in 68 percent and a 1-year overall survival of 65 percent. Because bortezomib has been reported to increase the severity of heart failure in myeloma, it is clearly a concern that requires monitoring in patients. The oral proteasome inhibitor MLN9708, ixazomib, is currently under investigation.

Bortezomib and dexamethasone have been used as consolidation therapy following stem cell transplantation.⁷⁷ Forty patients were transplanted with risk-adapted melphalan; patients with less than a complete response received consolidation with bortezomib-dexamethasone. Survivals at 12 and 24 months post treatment were 88 and 82 percent, respectively. Of the original 40 patients, 23 received consolidation, and their response was enhanced in 20 (86 percent). Organ response occurred in 70 percent at 24 months. The use of bortezomib-dexamethasone consolidation following stem cell transplantation can help deepen the response in patients that do not achieve a complete response.

In spite of the introduction of new agents, late diagnosis, particularly of cardiac amyloid, remains a major barrier to improvement in the overall survival of patients; and despite recent improvements in survival, 40 percent of patients succumb to the disease within the first year after diagnosis, and this early mortality has not changed in 30 years. Patients can have a hematologic response and still die of end-organ damage because it is impossible to repair the tissue damage that has occurred prior to diagnosis.^64,65 The prognosis in amyloidosis is determined by two primary factors. The first is the extent of cardiac involvement, and the second is the plasma cell burden seen in these patients. The former, historically measured by echocardiography, is more reproducibly measured by the use of cardiac biomarkers. The percentage of plasma cells in the marrow has an important impact on prognosis.^9,62 The best surrogate and the most reproducible way to measure the plasma cell burden is to look at the difference between the involved and uninvolved light chains in the serum (dFLC). A four-stage prognostic model has been developed using measurements of NT-proBNP, troponin, and serum free light chains. One point each is assigned for a troponin T level of 0.025 ng/mL or greater, an NT-proBNP greater than 1800 pg/mL, and a free light chain difference of greater than 180 mg/L. This provides almost four equal-size groups (if you have none of the 3 its stage 1; if you have 1 its stage 2; if you have 2 its stage 3 and if you have all 3 its stage 4) with median overall survivals of 94, 40, 14, and 6 months, respectively. These serum tests are currently the standard for assessing prognosis in amyloidosis. Assessing response in amyloidosis is a twofold process. First, the hematologic response is assessed by determining the reduction of the plasma cell burden and of the production of precursor amyloid light chains achieved by systemic therapy. There are four classes of response: (1) complete remission defined by negative immunofixation of serum and urine and a normal immunoglobulin free light-chain ratio; (2) a very good partial response that requires the difference between involved and uninvolved serum free light chain be less than 40 mg/L; (3) a partial response is defined as a 50 percent decrease from baseline in the dFLC; and (4) failure to respond includes all other patients. Light-chain assessment is not only the ideal method for measuring response because of the rapid decline in levels if therapy is effective, but it is better than the intact immunoglobulin as a measure of response when both are present.⁶³ Although hematologic response is the first goal, the purpose of therapy is preservation of organ function. Therefore, to have a meaningful impact, an organ response should be seen. Current data indicate that organ response rates are directly linked to hematologic response rates; and the deeper the hematologic response, the more likely there will be an organ response. A renal response is defined as a 50 percent decrease in 24-hour urine protein. The decrease must be no less than 0.5 g/day without a change in serum creatinine. A 50 percent increase in urinary protein loss to at least 1 g/day or a 25 percent worsening of creatinine clearance is indicative of progression. Cardiac response is defined primarily by changes in the NT-proBNP. A 30 percent reduction in the NT-proBNP, a minimum of 300 ng/L in patients whose baseline NT-proBNP is greater than 650 ng/L, constitutes a response. However, we have seen patients in whom fluctuations of the NT-proBNP of as much as 30 percent can occur as a result of changes in diuretics or the development of superimposed pulmonary infections that are unrelated to true changes in cardiac function; consequently, some caution is warranted in interpreting the results. An improvement in New York Heart Association class by two stages from 4 to 2 or 3 to 1 also is considered a response. Historically, echocardiography has been used to assess response, but interobserver variability has rendered it less useful and echocardiography is not currently part of response criteria. Cardiac progression constitutes a 30 percent increase in NT-proBNP, a minimum increase of 300 ng/dL. Finally, liver response is defined as a 50 percent reduction in the abnormal alkaline phosphatase value, with progression defined as a 50 percent increase of alkaline phosphatase above the lowest recorded value. Currently, consensus criteria to define response in soft tissues, the gastrointestinal tract, the tongue, the lung, or the peripheral nerve do not exist for AL amyloidosis.