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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:
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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
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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.
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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.
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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.
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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).
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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.
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DIFFERENTIAL DIAGNOSIS
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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.
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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.
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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.
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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.
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DIAGNOSIS AND CLINICAL CHARACTERIZATION OF ORGAN-SPECIFIC SYNDROMES
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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
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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.
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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
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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.
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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.
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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.
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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).
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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.
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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
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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
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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
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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
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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.
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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.
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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.
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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.