Nicholas Braus, MS2
School of Medicine and Dentistry
University of Rochester
4.4.08
Clinical Practice Essay
DL is a 56 year-old female who complained of shortness of breath on exertion over the last 6 months.
She had been a smoker and therefore pulmonary function tests were done and showed a pattern typical
of moderate restrictive lung disease (FEV1 of 58% predicted, FVC of 65% predicted). A chest
radiograph showed normal lung fields. A CT scan was also performed, which showed diffuse groundglass infiltrates bilaterally. There was no adenopathy. A bronchoscopy and trans-bronchial biopsy was
done that revealed normal airways, but thickened alveolar septae with amorphous eosinophilic
deposition, positive for Congo red and Crystal violet staining, consistent with amyloidosis. Serum
protein electrophoresis indicated a paraprotein in the near gamma region in a concentration of 1.6 g/dL
exhibiting IgG Lambda reactivity. Urine electrophoresis showed free light chains. What further
evaluation is needed and how should her care be managed?
The Clinical Problem
Amyloidosis describes a constellation of rare diseases that arise as a result of the deposition of a
pathologic protinaceous substance in extracellular tissue. Tissues commonly involved include the
kidneys (33%), heart (25%), peripheral and autonomic nerves (17%), gastrointestinal tract (8%), skin,
joints, and blood vessels.1 The protean clinical features of amyloidosis, together with its biochemical
and pathological heterogeneity, make its epidemiology challenging to define with precision.
Classification of the disease is based on the biochemical profile of the precursor proteins that give rise to
abnormal fibrillar protein deposits.
Epidemiology & Nosology of Systemic Amyloidoses
Of the systemic forms of the disease, so called “AL” or “Primary Amyloidosis” is the most
common and arises from the deposition of amyloidogenic monoclonal immunoglobulin light chains. It
has an age-adjusted incidence of 8.9 per million person-years and accounts for approximately 60% of all
cases of amyloidosis.2 AL amyloidosis can occur in association with any form of monoclonal B cell
dyscrasia, and it occurs in 12-15% of patients with multiple myeloma.3 Another systemic variant is
“AA” or “Secondary Amyloidosis”, which derives from cleavage, misfolding and aggregation of the
acute phase reactant serum amyloid A protein. It is a potential complication of any chronic inflammatory
state and accounts for approximately 10% of cases.4 Familial Amyloidoses are a group of autosomal
1
dominant diseases in which amyloid deposition is derived from a mutant form of transthyretin (TTR), a
transport protein for thyroxin and retinol-binding protein. Senile cardiac amyloidosis and familial
amyloid cardiomyopathy are both associated with abnormal transthyretin. The incidence of familial
transthyretin-associated amyloidosis is unknown, however it has been reported that the number of cases
diagnosed in referral centers is approximately 10-20% that of AL amyloidosis.5 One analysis of the
amyloidogenic transthyretin Ile 122 mutation found an allelic frequency of 0.020 in black Americans,
indicating that 1.3 million black Americans carry the allele.6 Patients on long-term hemodialysis are at
risk for an amyloidosis that derives from the deposition of circulating -2 microglobulin in subchondral
bone and the synovia of joints and tendons. The prevalence of this type of amyloidosis has been
observed in over 50% of patients at 165 months of dialysis treatment and approaches 100% in patients
with over 20 years of treatment.7 Common manifestations of -2m amyloidosis include carpal tunnel
syndrome and bone cysts. Finally, deposition of -amyloid (A) in brain tissue has been demonstrated
to play a central role in the pathophysiology of Alzheimer’s Disease, which affects over 4.5 million
Americans.8 -amyloid is a metabolic byproduct of “amyloid precursor protein” (APP), an integral
membrane protein expressed in many tissues and concentrated in the synapses of neurons.9
Pathophysiology of Amyloid Deposition
As noted above, the central pathophysiologic mechanism in systemic amyloidosis is formation
and deposition of amyloid proteins in extracellular tissues. Despite its uniform appearance and tinctorial
characteristics under electron, light, and polarizing microscopy, “amyloid” is not a chemically distinct
entity. Rather, it describes a family of over 20 proteins that assume an insoluble -pleated fibrillar
conformation under certain conditions. It is precisely this underlying biochemical heterogeneity of
amyloid that gives rise to the disease’s strikingly heterogeneous clinical phenotypes.
The molecular mechanism that conjugates precursor proteins into -fibrils is closely related to
physiologic protein folding, in which newly synthesized peptide chains undergo a rapid sequence of
conformational changes in the cytoplasm and become either native or misfolded proteins. The intrinsic
2
propensity for a protein to assume an amyloidogenic conformation is determined by the interaction of
pro-fibrillar and anti-fibrillar characteristics. An abundance of residues favoring -pleated sheet
conformation, poor stability of the protein’s native conformation, abundant hydrophobic side chains, and
neutralization of charges on amino acid residues have all been identified as pro-fibrillar attributes of
amyloidogenic proteins, while interruption of -sheets with residues like proline and the repulsion of
amino acid residues with the same charge are characteristics that inhibit fribrillogeneis. 10 Beyond these
intrinsic qualities, proteolytic remodeling and mutation have also been proposed as mechanisms of
fibrillogenesis.11 Mutations contribute to amyloidogenicity by destabilizing critical regions of a
protein’s structure and rendering it prone to fibrillar aggregation. For example, during the immune
response lambda light chain variable domains of immunoglobulins mutate extensively and a small
fraction of the final light chain proteins produced by this process are amyloidogenic. When such end
products are produced extensively—as in the case of myeloma—they aggregate and deposit in tissue,
and primary (AL) amyloidosis is the result. The role of proteolysis in the pathogenesis of amyloid
deposition disorders is exemplified by the cleavage of the 753-residue amyloid precursor protein (APP)
into fragments of 39 to 43 residues, which make up the amyloid plaques found in Alzheimer’s Disease.
Additional non-fibrillar components of the molecular mechanism of amyloid production are the
glycoprotein “serum amyloid P” and proteoglycans like haparan and and dermatan sulfate. These
components are expressed in all amyloid deposits, regardless of the protein of origin or the tissue
involved. Proteoglycans make up the carbohydrate component of amyloid, and it has been postulated
that they act as a scaffolding to stabilize amyloid fibrils and facilitate aggregation. 12 Serum amyloid P
(SAP) binds to a site common to all conformational varieties of amyloid, which has not yet been
elucidated. SAP is considered important in the pathogenesis of amyloidosis because of it’s
demonstrated ability to protect misfolded protein from degradation by proteases and resorption via
normal cellular mechanisms of protein homeostasis. 13 The development of radio-labeled SAP
3
scintigraphy has led to advances in diagnosis and treatment by allowing non-invasive imaging and
quantitative monitoring of disease progression.14
The pathological effects of amyloid deposition are mainly a result of the physical presence of
excess non-soluble proteinaceous material in affected tissues. Normally, inappropriately aggregated or
misfolded extracellular proteins are degraded by macrophages. In amyloidosis, however, normal
molecular surveillance and proteolytic mechanisms fail, and serum amyloid proteins accumulate,
aggregate, and are ultimately deposited in tissues. Accumulation of substantial protein deposits can
disrupt tissue architecture, disrupt normal vessel wall dynamics, create space-occupying lesions, and
impair organ function. Smaller deposits in specific tissues (e.g. glomeruli, cardiac conductive fibers,
nerves) can also produce significant pathology. Although prognosis correlates well with overall amyloid
burden, there is little evidence to support a correlation between severity of symptoms and the scale of
deposits.15 Interestingly, histological evidence of inflammation is rare in amyloidosis. There is,
however, some evidence from experiments in vitro that newly forming amyloid fibrils are cytotoxic and
induce cell death by apoptosis and necrosis.16 This recent discovery is consistent with the reported
clinical correlation between periods of active amyloid deposition and accelerated deterioration of
tissues.17
Traditionally the natural history of amyloidosis has been understood as an unremitting and
irreversible process of protein deposition with progressive functional decline of involved tissues. A
population-based study of primary (AL) amyloidosis at Mayo Clinic reported a median survival time
after diagnosis of 2.3 years.18 Contrary to the irreversible progression of the disease, however, serial
SAP scintigraphic studies shown that amyloid deposits exist in a state of dynamic turnover. AL, AA, 2m, and TTR amyloid deposits have all been demonstrated to regress when the supply of precursor
proteins is eliminated.19,20,21,22 This discovery is encouraging, although its implications for the treatment
of amyloid deposition disorders is not yet clear.
4
Amyloidosis in the respiratory tract
As first recorded by Virchow and Lesser in 1857, amyloidosis may affect any structure within
the thorax including the lung parenchyma and respiratory tract.23 Pulmonary involvement in systemic
disease is common and almost exclusively associated with primary (AL) amyloidosis. In fact,
microscopic deposits of amyloid in the lungs are almost universally present at autopsy in patients with
AL amyloidosis.24, 25 Clinically, however, this association is not always apparent as less than 10-20% of
patients with AL amyloidosis present with significant respiratory symptoms. In addition, it has been
demonstrated that in most cases amyloid-associated dyspnea is secondary to cardiac involvement.26
Since the advent of antimicrobial therapy, the prevalence of secondary (AA) pulmonary amyloidosis has
declined significantly. Today the respiratory diseases underlying secondary pulmonary amyloidosis are
bronchiectasis, tuberculosis, and Mediterranean fever.27 Pulmonary TTR-associated amyloidosis has
been rarely reported and its clinical significance, if any, has yet to be established.28
Focal amyloidoses of the respiratory tract are almost exlusively of the AL type, and can be seen
in the larynx, trachea, large bronchi, and the parenchymal tissue of the lung. Localized lesions, or
“amyloidomas,” are almost never manifestations of systemic primary amyloidosis. Whereas
amyloidogenic light chains in systemic AL amyloidosis clearly derive from circulating monoclonal light
chains produced by plasma cell dyscrasias, studies of localized AL amyloidoses demonstrate that light
chains in this type arise from very subtle focal lymphoplasmacytic proliferation confined to areas in
proximity to amyloid deposits.29 Despite this observation, it is recommended that all patients with focal
lesions be evaluated for signs of systemic disease.30
Amyloid deposition within the lung parenchyma, sometimes referred to as “alveolar septal
amyloidosis,” stands out from other focal amyloidoses of the airways because of its two distinct
presentations, each with separate epidemiological and pathophysiological profiles. Nodular amyloidosis
in the lung parenchyma is usually an incidental finding and is not associated with systemic disease.
Diffuse alveolar septal amyloidosis is usually a manifestation of systemic AL amyloidosis. 31 As
5
mentioned above, diffuse involvement of the lung parenchyma is considered the rule rather than the
exception in systemic primary (AL) amyloidosis, making it by far the most prevalent form of pulmonary
amyloidosis.
Strategies and Evidence
Diagnosis
Diffuse alveolar septal amyloidosis usually presents with a history of progressive dyspnea and
cough. Anatomical and functional evaluation should include plain radiographic and CT studies of the
chest, bronchoscopy and pulmonary function tests. Plain films of the chest typically show diffuse
reticulo-nodular infiltrates and occasionally hilar and mediastinal lymph nodes. CT scans show
widespread interstitial involvement, occasionally with calcification.32 Pulmonary function tests may
demonstrate a decline in lung volumes and diffusion capacity.
The gold standard for diagnosis of amyloidosis is the apple-green birefringence seen when
involved tissue is stained with Congo red dye and viewed under polarized light.33 Tissue specimens can
be collected via small needle biopsy, though compared to open surgical resection this method entails
significant sampling error.34 A reported risk of endo- and transbronchial biopsy is excessive bleeding
due to increased fragility of involved blood vessles, reduced elasticity of involved parenchymal tissue,
and very rarely an acquired clotting factor deficiency.35 When tissue biopsy is contraindicated, an
effective alternative is abdominal fat pad aspiration cytology.36
Positive histology does not, however, provide information regarding the underlying protein type,
systemic involvement, or the natural history of the disease. Identification of underlying systemic disease,
including clonal plasma cell dyscrasias, must be sought via hematological and biochemical assays such
as serum and urine protein electrophoresis. Due to the prevalence of monoclonal gammopathy of
undertermined significance (MGUS), demonstration of monoclonal gammopathy and serum or urine
light chains is not definitive evidence of AL amyloidosis and should not preclude immunohistochemical
analysis to determine the protein of origin. In the absence of a plasma cell dyscrasia and
6
immunohistochemical evidence of AA protein, evidence of a transthyretin-associated amyloidosis
should be sought using isoelectric focusing of the serum for abnormal TTR.37 Additional testing in the
case of systemic disease includes tests for organ involvement such as liver enzyme assays, nerve
conduction studies, and echocardiography. Finally, routine monitoring of the whole body load and
distribution of amyloid deposits should be carried out using radiolabeled SAP scintigraphy. Intravenous
radiolabeled SAP localizes to areas with high concentrations of amyloid-associated SAP, and facilitates
the determination of the disease’s natural history and response to treatment in individual cases.38
Treatment
Treatment options for alveolar septal AL amyloidosis are limited, and due to the paucity of
randomized controlled trials treatment decisions are typically made on an empirical basis. Management
is oriented around preservation of organ function and aggressive measures to reduce the rate of protein
deposition. Treatment with steroids and irradiation has not been proven to influence the course of the
disease, however in AL amyloidosis chemotherapy with combination melphalan and prednisone has
been demonstrated to suppress the underlying dyscrasia and slow the rate of deposition in up to 30% of
patients.39 Cytotoxic regimens have been reported to increase median survival time from 15 months in
untreated patients to over 5 years in those receiving treatment.40 A recent study has also demonstrated
the effectiveness of vincristine, doxorubicin, and dexamethasone (VAD) alone in high-risk patients with
AL amyloidosis-related nephrotic syndrome.41 Autologous stem cell and bone marrow transplantation
protocols have been developed with mixed success. A major limiting factor in these therapies is a
relatively high treatment-related mortality rate, which is estimated to be between 10-20%.42
Areas of Uncertainty
Fibrillogenesis stands out as an area of basic science research with great potential to contribute to
the diagnosis and care of patients with amyloidoses, including Alzheimer’s Disease and perhaps even
related proteinoses like prion diseases. A greater understanding the basic mechanisms determining the
molecular stability of proteins and their propensity to assume pathological conformations has begun to
7
point medical research towards strategies for inhibiting the process. Research into these mechanisms
has focused on the role of proteoglycans, chaperonins, and glycosaminoglycans (SAP) in stabilizing
proteins in misfolded states.43 In addition, the pursuit of small molecule inhibitors of amyloid
fibrillogenesis is very active in the development of new therapies for Alzheimer’s Disease.44
Conclusions and Recommendations
Primary (AL) amylodiosis is a rare protein-deposition disorder caused by a monoclonal plasma cell
dyscrasia. Clinically it follows a progressive and unremitting course with poor prognosis and limited
treatment options. For patients with symptomatic organ dysfunction, such as the woman in the vignette,
treatment should be guided by accurate characterization of the underlying proteinopathy with
immunohistochemical staining, and the extent of her dyscrasia with peripheral blood smear and bone
marrow biopsy. I would monitor her lung function and rigorously screen for extrapulmonary organ
dysfunction, paying close attention to the kidneys, heart and liver. I would also routinely monitor her
whole-body load and distribution of amyloid deposits with radiolabelled SAP scintigraphy.
In one
univariate analysis, bone marrow plasma cell percentage over 10%, circulating plasma cell percentage
over 1%, and peripheral blood plasma cell count over 500,000/L (0.5/miroL), and prominent cardiac
involvement each predicted for significantly worse overall survival. 45 Combination chemotherapy with
melphalan and prednisone is recommended. Additional treatment modalities such as hematopoietic cell
transplant and research protocols for combination chemotherapy and/or hematopoietic cell transplant
may be considered.
1
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38
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39
Kyle R., Gertz M., et al. “A trial of three regimens for primary amyloidosis: colchicine
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Matsuda M., Gono T., et al. “Nephrotic syndrome due to primary systemic AL
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30
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