Amyloidosis
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AMYLOIDOSIS
Extracellular deposition of fibrillar proteins which are responsible for tissue damage and functional compromise.
These abnormal fibrils are produced by the aggregation of misfolded proteins (which are soluble in their normal folded configuration)
The fibrillar deposits bind a wide variety of proteoglycans and glycosaminoglycans, including heparan sulfate and dermatan sulfate, and plasma proteins, notably serum amyloid P component (SAP).
The presence of abundant charged sugar groups in these adsorbed proteins give the deposits staining characteristics that were thought to resemble starch (amylose). Therefore, the deposits were called amyloid,
PATHOGENESIS
Amyloidosis is fundamentally a disorder of protein misfolding.
Amyloid is not a structurally homogeneous protein, more than 20 (at last count, 23) different proteins can aggregate and form fibrils with the appearance of amyloid.
Regardless of their derivation, all amyloid deposits are composed of nonbranching fibrils, 7.5 to 10 nm in diameter, each formed of βsheet polypeptide chains that are wound together .
The dye Congo red binds to these fibrils and produces a red-green dichroism (birefringence), which is commonly used to identify amyloid desposits in tissues
Several factors may contribute to the aggregation of certain proteins and the formation of fibrils that deposit in extracellular tissues
The protein may have a tendency to form aggregates of misfolded forms but does so only when its concentration reaches abnormally high levels.
This may happen as an individual ages (senile amyloidosis), or when its production is increased (e.g., in chronic inflammatory states), or if excretion of the protein is impaired (amyloidosis associated with long-term dialysis).
A mutation may give rise to a form of a protein that has a tendency to fold improperly and form aggregates (hereditary amyloidosis).
Limited proteolysis may generate a protein that forms amyloid fibrils (amyloidosis associated with Alzheimer disease).
Of the more than 20 biochemically distinct forms of amyloid proteins that have been identified, three are most common:
1) The AL (amyloid light chain) protein is produced by plasma cells and is made up of complete immunoglobulin (Ig) light chains, the aminoterminal fragments of light chains, or both.
Only a few types of Ig light chains are prone to forming aggregates, probably because they contain amino acid residues that destabilize the domain structure. As expected, the deposition of amyloid fibril protein of the AL type is associated with some form of monoclonal B-cell proliferation
2) The AA (amyloid-associated) fibril is a unique nonimmunoglobulin protein derived from a larger (12-kD) serum precursor called SAA (serum amyloid-associated) protein that is synthesized in the liver..
Increased production of SAA is probably not sufficient to generate amyloid deposits. It is believed that SAA is normally degraded to soluble end products by macrophage-derived enzymes. Defective proteolysis may produce misfolded, incompletely degraded SAA, leading to aggregation and deposition as AA fibrils.
The production of this protein is increased in inflammatory states as part of the "acute phase response"; therefore this form of amyloidosis is associated with chronic inflammatory disorders
3) Aβ amyloid is found in the cerebral lesions of Alzheimer disease.
Aβ is a 4-kD peptide that constitutes the core of cerebral plaques and the amyloid deposits in cerebral blood vessels in this disease.
The Aβ protein is derived from a much larger transmembrane glycoprotein called amyloid precursor protein (APP)
Several other proteins have been found in amyloid deposits in a variety of clinical settings:
Transthyretin (TTR) is a normal serum protein that binds and transports thyroxine and retinol, hence the name. Mutations in the gene encoding transthyretin result in the production of a protein (and its fragments) that aggregate and form amyloid deposits. The resultant diseases are called familial amyloid polyneuropathies
Transthyretin is also deposited in the heart of aged individuals (senile systemic amyloidosis); in such cases the protein is structurally normal, but it accumulates at high concentrations.
Some cases of familial amyloidosis are associated with deposits of mutant lysozyme
β2-microglobulin, a component of the MHC class I molecules and a normal serum protein, has been identified as the amyloid fibril subunit (Aβ2m) in amyloidosis that complicates the course of patients on long-term hemodialysis.
This protein is present in high concentrations in the serum of patients with renal disease and is retained in the circulation because it is not efficiently filtered through dialysis membranes.
In some series, as many as 60% to 80% of patients on long-term dialysis developed amyloid deposits in the synovium, joints, and tendon sheaths
Amyloid deposits derived from diverse precursors such as hormones (procalcitonin) and keratin have also been reported.
CLASSIFICATION
May be systemic or localized, On clinical grounds, the systemic is subclassified into primary amyloidosis when associated with some immunocyte dyscrasia, or secondary amyloidosis when it occurs as a complication of an underlying chronic inflammatory or tissue destructive process. Hereditary or familial amyloidosis
PRIMARY AMYLOIDOSIS
Usually systemic in distribution and is of the AL type.
The most common form of amyloidosis.
Eg: amyloidosis associated with multiple myeloma The malignant B cells characteristically synthesize abnormal amounts of a single specific Ig (monoclonal gammopathy), producing an M (myeloma) protein spike on serum electrophoresis
In addition to the synthesis of whole Ig molecules, plasma cells may also synthesize and secrete either the γ or κ light chain, also known as Bence Jones proteins
These are present in the serum of as many as 70% of patients with multiple myeloma, and almost all patients with myeloma who develop amyloidosis have Bence Jones proteins in the serum or urine, or both.
Only 6% to 15% of myeloma patients who have free light chains develop amyloidosis.
The presence of Bence Jones proteins, though necessary, is by itself not sufficient to produce amyloidosis.
Other variables, such as the type of light chain produced and its catabolism, contribute to the "amyloidogenic potential" and influence the deposition of Bence Jones proteins.
The great majority of patients with AL amyloid do not have classic multiple myeloma or any other overt B-cell neoplasm;
such cases are nevertheless classified as primary amyloidosis because their clinical features derive from the effects of amyloid deposition without any other associated disease.
In virtually all such cases, patients have a modest increase in the number of plasma cells in the bone marrow, and monoclonal immunoglobulins or free light chains can be found in the serum or urine.
Clearly, these patients have an underlying B-cell dyscrasia in which production of an abnormal protein, rather than production of tumor masses, is the predominant manifestation.
Reactive Systemic Amyloidosis
Systemic in distribution and are composed of AA protein.
This category was previously referred to as secondary amyloidosis, because it is secondary to an associated inflammatory condition.
The feature common to most cases of reactive systemic amyloidosis is protracted cell injury occurring in a spectrum of infectious and noninfectious chronic inflammatory conditions. Classically, tuberculosis, bronchiectasis, and chronic osteomyelitis were the most common causes
most frequently in the setting of chronic inflammation caused by autoimmune states (e.g., RA, ankylosing spondylitis, and inflammatory bowel disease
RA is particularly prone to develop amyloidosis, with amyloid deposition seen in as many as 3% of such patients.
Chronic skin infections caused by "skin-popping" of narcotics are also associated with amyloid deposition.
May also occur in association with tumors not derived from immune cells, the two most common being renal cell carcinoma and Hodgkin lymphoma.
Familial (Hereditary) Amyloidosis Most are rare and occur in limited geographic areas.
The best characterized is an autosomal recessive condition called familial Mediterranean fever. This is a febrile disorder characterized by attacks of fever accompanied by inflammation of serosal surfaces, including peritoneum, pleura, and synovial membrane.
This disorder is encountered largely in individuals of Armenian, Sephardic Jewish, and Arabic origins
Associated with widespread tissue involvement
The amyloid fibril proteins are made up of AA proteins, suggesting that this form of amyloidosis is related to the recurrent bouts of inflammation that characterize this disease.
The gene for familial Mediterranean fever has been cloned, and its product is called pyrin; although its exact function is not known, it has been suggested that pyrin is responsible for regulating acute inflammation, presumably by inhibiting the function of neutrophils.
With a mutation in this gene, minor traumas unleash a vigorous, tissue-damaging inflammatory response.
In contrast to familial Mediterranean fever, a group of autosomal dominant familial disorders is characterized by deposition of amyloid predominantly in the peripheral and autonomic nerves.
These familial amyloidotic polyneuropathies have been described in kindreds in different parts of the world, for example, in Portugal, Japan, Sweden, and the US.
Localized Amyloidosis The deposits may produce grossly detectable nodular masses or be evident only on microscopic examination. Nodular (tumor-forming) deposits of amyloid are most often encountered in the lung, larynx, skin, urinary bladder, tongue, and the region about the eye. Frequently, there are infiltrates of lymphocytes and plasma cells in the periphery of these amyloid masses. At least in some cases, the amyloid consists of AL protein and may therefore represent a localized form of immunocyte-derived amyloid.
Endocrine Amyloid Microscopic deposits of localized amyloid may be found in certain endocrine tumors, such as medullary carcinoma of the thyroid gland, islet tumors of the pancreas, pheochromocytomas, undifferentiated carcinomas of the stomach in the islets of Langerhans in patients with type 2 diabetes mellitus.
In these settings, the amyloidogenic proteins seem to be derived either from polypeptide hormones (medullary carcinoma) or from unique proteins (e.g., islet amyloid polypeptide).
Amyloid of Aging Senile systemic amyloidosis refers to the systemic deposition of amyloid in elderly patients (usually in their 70s and 80s).
Because of the dominant involvement and related dysfunction of the heart (typically presenting as a restrictive cardiomyopathy and arrhythmias), this form is also called senile cardiac amyloidosis.
The amyloid in this form is composed of the normal TTR molecule.
In addition, another form predominantly affecting only the heart results from the deposition of a mutant form of TTR.
Approximately 4% of the black population in the United States is a carrier of the mutant allele, and cardiomyopathy has been identified in both homozygous and heterozygous patients
MORPHOLOGY:
In amyloidosis secondary to chronic inflammatory disorders, kidneys, liver, spleen, lymph nodes, adrenals, and thyroid, as well as many other tissues, are typically affected.
Immunocyte-associated amyloidosis more often involves the heart, gastrointestinal tract, respiratory tract, peripheral nerves, skin, and tongue.
The amyloidosis may or may not be apparent on macroscopic examination.
Often small amounts are not recognized until the surface of the cut organ is painted with iodine and sulfuric acid. This yields mahogany brown staining of the amyloid deposits.
When amyloid accumulates in larger amounts, the organ is frequently enlarged and the tissue appears gray with a waxy, firm consistency.
Histologically, the amyloid deposition is always extracellular and begins between cells, often closely adjacent to basement membranes.
As the amyloid accumulates, it encroaches on the cells, in time surrounding and destroying them.
In the immunocyte-associated form, perivascular and vascular localizations are common
The histologic diagnosis of amyloid is based almost entirely on its staining characteristics.
The most commonly used staining technique uses the dye Congo red, which under ordinary light imparts a pink or red color to amyloid deposits. Under polarized light the Congo red-stained amyloid shows so-called apple-green birefringence
. This reaction is shared by all forms of amyloid and is caused by the crossed β-pleated configuration of amyloid fibrils
Confirmation can be obtained by electron microscopy, which reveals amorphous nonoriented thin fibrils.
AA, AL, and ATTR types of amyloid can also be distinguished by specific immunohistochemical staining.
Kidney Amyloidosis of the kidney is the most common and most serious involvement in the disease.
Grossly, the kidney may appear unchanged, or it may be abnormally large, pale, gray, and firm; in long-standing cases, the kidney may be reduced in size.
Microscopically, the amyloid deposits are found principally in the glomeruli, but they are also present in the interstitial peritubular tissue as well as in the walls of the blood vessels.
The glomerulus first develops focal deposits within the mesangial matrix and diffuse or nodular thickenings of the basement membranes of the capillary loops.
With progression, the deposition encroaches on the capillary lumina and eventually leads to total obliteration of the vascular tuft
The interstitial peritubular deposits are frequently associated with the appearance of amorphous pink casts within the tubular lumens, presumably of a proteinaceous nature.
Amyloid deposits may develop in the walls of blood vessels of all sizes, often causing marked vascular narrowing
Spleen Moderate or even marked enlargement(200-800gm).
One of two patterns may develop. The deposits may be virtually limited to the splenic follicles, producing tapioca-like granules on gross examination ("sago spleen"), or the involvement may affect principally the splenic sinuses and eventually extend to the splenic pulp, forming large, sheetlike deposits ("lardaceous spleen"). In both patterns the spleen is firm in consistency, and cut surfaces reveal pale gray, waxy deposits
Liver Massive enlargement (as much as 9000 gm). In such advanced cases the liver is extremely pale, grayish, and waxy on both the external surface and the cut section. Histologically, amyloid deposits first appear in the space of Disse and then progressively enlarge to encroach on the adjacent hepatic parenchyma and sinusoids
The trapped liver cells undergo compression atrophy and are eventually replaced by sheets of amyloid; function may be preserved even in the setting of severe involvement
Heart
Either as isolated organ involvement or as part of a systemic distribution.
When accompanied by systemic involvement, it is usually associated with immunocyte dyscrasias.
The isolated form (senile amyloidosis) is usually confined to older individuals..
The deposits may not be evident on gross examination, or they may cause minimal to moderate cardiac enlargement
The most characteristic gross findings are gray-pink, dewdrop-like subendocardial elevations, particularly evident in the atrial chambers.
On histologic examination, deposits are typically found throughout the myocardium, beginning between myocardial fibers and eventually causing their pressure atrophy
Other Organs Encountered in systemic disease.
The adrenals, thyroid, and pituitary are common sites . In this case also the amyloid deposition begins in relation to stromal and endothelial cells and progressively encroaches on the parenchymal cells.
Surprisingly, large amounts of amyloid may be present in any of these endocrine glands without apparent disturbance of function.
In the gastrointestinal tract, a relatively favored site, amyloid may be found at all levels, sometimes producing tumorous masses that must be distinguished from neoplasms.
Nodular depositions in the tongue may produce macroglossia.
On the basis of the frequent involvement of the gastrointestinal tract in systemic cases, gingival, intestinal, and rectal biopsies serve in the diagnosis of suspected cases.
Deposition of β2-microglobulin amyloid in patients receiving long-term dialysis occurs most commonly in the carpal ligaments of the wrist, resulting in compression of the median nerve (carpal tunnel syndrome
CLINICAL FEATURES
Nonspecific complaints such as weakness, fatigue, and weight loss are the most common initial symptoms. Later by renal disease, hepatomegaly, splenomegaly, or cardiac abnormalities. Renal involvement giving rise to severe proteinuria is often the major cause of symptoms in reactive systemic amyloidosis. Progression of the renal disease may lead to renal failure, which is an important cause of death in amyloidosis..
The hepatosplenomegaly rarely causes significant clinical dysfunction, but it may be the presenting finding.
Cardiac amyloidosis may manifest as conduction disturbances or as restrictive cardiomyopathy Cardiac arrhythmias are an important cause of death in cardiac amyloidosis
The diagnosis of amyloidosis may be suspected from the clinical signs and symptoms and from some of the findings mentioned;
Biopsy and subsequent Congo red staining is the most important tool in the diagnosis of amyloidosis.
In general, biopsy is taken from the organ suspected to be involved. For example, renal biopsy is useful in the presence of urinary abnormalities. Rectal and gingival biopsy specimens contain amyloid in as many as 75% of cases with generalized amyloidosis.
Examination of abdominal fat aspirates stained with Congo red is a simple, low-risk method.
In suspected cases of AL amyloidosis, serum and urinary protein electrophoresis and immunoelectrophoresis should be performed.
Bone marrow aspirate in such cases usually shows plasmacytosis, even if skeletal lesions of multiple myeloma are not present
The outlook for patients with generalized amyloidosis is poor, with the mean survival time after diagnosis ranging from 1 to 3 years.
In AA amyloidosis, the prognosis depends to some extent on the control of the underlying condition. Patients with myeloma-associated amyloidosis have a poorer prognosis, although they may respond to cytotoxic drugs used to treat the underlying disorder.
Resorption of amyloid after treatment of the associated condition has been reported, but this is a rare occurrence.
Extracellular deposition of fibrillar proteins which are responsible for tissue damage and functional compromise.
These abnormal fibrils are produced by the aggregation of misfolded proteins (which are soluble in their normal folded configuration)
The fibrillar deposits bind a wide variety of proteoglycans and glycosaminoglycans, including heparan sulfate and dermatan sulfate, and plasma proteins, notably serum amyloid P component (SAP).
The presence of abundant charged sugar groups in these adsorbed proteins give the deposits staining characteristics that were thought to resemble starch (amylose). Therefore, the deposits were called amyloid,
PATHOGENESIS
Amyloidosis is fundamentally a disorder of protein misfolding.
Amyloid is not a structurally homogeneous protein, more than 20 (at last count, 23) different proteins can aggregate and form fibrils with the appearance of amyloid.
Regardless of their derivation, all amyloid deposits are composed of nonbranching fibrils, 7.5 to 10 nm in diameter, each formed of βsheet polypeptide chains that are wound together .
The dye Congo red binds to these fibrils and produces a red-green dichroism (birefringence), which is commonly used to identify amyloid desposits in tissues
Several factors may contribute to the aggregation of certain proteins and the formation of fibrils that deposit in extracellular tissues
The protein may have a tendency to form aggregates of misfolded forms but does so only when its concentration reaches abnormally high levels.
This may happen as an individual ages (senile amyloidosis), or when its production is increased (e.g., in chronic inflammatory states), or if excretion of the protein is impaired (amyloidosis associated with long-term dialysis).
A mutation may give rise to a form of a protein that has a tendency to fold improperly and form aggregates (hereditary amyloidosis).
Limited proteolysis may generate a protein that forms amyloid fibrils (amyloidosis associated with Alzheimer disease).
Of the more than 20 biochemically distinct forms of amyloid proteins that have been identified, three are most common:
1) The AL (amyloid light chain) protein is produced by plasma cells and is made up of complete immunoglobulin (Ig) light chains, the aminoterminal fragments of light chains, or both.
Only a few types of Ig light chains are prone to forming aggregates, probably because they contain amino acid residues that destabilize the domain structure. As expected, the deposition of amyloid fibril protein of the AL type is associated with some form of monoclonal B-cell proliferation
2) The AA (amyloid-associated) fibril is a unique nonimmunoglobulin protein derived from a larger (12-kD) serum precursor called SAA (serum amyloid-associated) protein that is synthesized in the liver..
Increased production of SAA is probably not sufficient to generate amyloid deposits. It is believed that SAA is normally degraded to soluble end products by macrophage-derived enzymes. Defective proteolysis may produce misfolded, incompletely degraded SAA, leading to aggregation and deposition as AA fibrils.
The production of this protein is increased in inflammatory states as part of the "acute phase response"; therefore this form of amyloidosis is associated with chronic inflammatory disorders
3) Aβ amyloid is found in the cerebral lesions of Alzheimer disease.
Aβ is a 4-kD peptide that constitutes the core of cerebral plaques and the amyloid deposits in cerebral blood vessels in this disease.
The Aβ protein is derived from a much larger transmembrane glycoprotein called amyloid precursor protein (APP)
Several other proteins have been found in amyloid deposits in a variety of clinical settings:
Transthyretin (TTR) is a normal serum protein that binds and transports thyroxine and retinol, hence the name. Mutations in the gene encoding transthyretin result in the production of a protein (and its fragments) that aggregate and form amyloid deposits. The resultant diseases are called familial amyloid polyneuropathies
Transthyretin is also deposited in the heart of aged individuals (senile systemic amyloidosis); in such cases the protein is structurally normal, but it accumulates at high concentrations.
Some cases of familial amyloidosis are associated with deposits of mutant lysozyme
β2-microglobulin, a component of the MHC class I molecules and a normal serum protein, has been identified as the amyloid fibril subunit (Aβ2m) in amyloidosis that complicates the course of patients on long-term hemodialysis.
This protein is present in high concentrations in the serum of patients with renal disease and is retained in the circulation because it is not efficiently filtered through dialysis membranes.
In some series, as many as 60% to 80% of patients on long-term dialysis developed amyloid deposits in the synovium, joints, and tendon sheaths
Amyloid deposits derived from diverse precursors such as hormones (procalcitonin) and keratin have also been reported.
CLASSIFICATION
May be systemic or localized, On clinical grounds, the systemic is subclassified into primary amyloidosis when associated with some immunocyte dyscrasia, or secondary amyloidosis when it occurs as a complication of an underlying chronic inflammatory or tissue destructive process. Hereditary or familial amyloidosis
PRIMARY AMYLOIDOSIS
Usually systemic in distribution and is of the AL type.
The most common form of amyloidosis.
Eg: amyloidosis associated with multiple myeloma The malignant B cells characteristically synthesize abnormal amounts of a single specific Ig (monoclonal gammopathy), producing an M (myeloma) protein spike on serum electrophoresis
In addition to the synthesis of whole Ig molecules, plasma cells may also synthesize and secrete either the γ or κ light chain, also known as Bence Jones proteins
These are present in the serum of as many as 70% of patients with multiple myeloma, and almost all patients with myeloma who develop amyloidosis have Bence Jones proteins in the serum or urine, or both.
Only 6% to 15% of myeloma patients who have free light chains develop amyloidosis.
The presence of Bence Jones proteins, though necessary, is by itself not sufficient to produce amyloidosis.
Other variables, such as the type of light chain produced and its catabolism, contribute to the "amyloidogenic potential" and influence the deposition of Bence Jones proteins.
The great majority of patients with AL amyloid do not have classic multiple myeloma or any other overt B-cell neoplasm;
such cases are nevertheless classified as primary amyloidosis because their clinical features derive from the effects of amyloid deposition without any other associated disease.
In virtually all such cases, patients have a modest increase in the number of plasma cells in the bone marrow, and monoclonal immunoglobulins or free light chains can be found in the serum or urine.
Clearly, these patients have an underlying B-cell dyscrasia in which production of an abnormal protein, rather than production of tumor masses, is the predominant manifestation.
Reactive Systemic Amyloidosis
Systemic in distribution and are composed of AA protein.
This category was previously referred to as secondary amyloidosis, because it is secondary to an associated inflammatory condition.
The feature common to most cases of reactive systemic amyloidosis is protracted cell injury occurring in a spectrum of infectious and noninfectious chronic inflammatory conditions. Classically, tuberculosis, bronchiectasis, and chronic osteomyelitis were the most common causes
most frequently in the setting of chronic inflammation caused by autoimmune states (e.g., RA, ankylosing spondylitis, and inflammatory bowel disease
RA is particularly prone to develop amyloidosis, with amyloid deposition seen in as many as 3% of such patients.
Chronic skin infections caused by "skin-popping" of narcotics are also associated with amyloid deposition.
May also occur in association with tumors not derived from immune cells, the two most common being renal cell carcinoma and Hodgkin lymphoma.
Familial (Hereditary) Amyloidosis Most are rare and occur in limited geographic areas.
The best characterized is an autosomal recessive condition called familial Mediterranean fever. This is a febrile disorder characterized by attacks of fever accompanied by inflammation of serosal surfaces, including peritoneum, pleura, and synovial membrane.
This disorder is encountered largely in individuals of Armenian, Sephardic Jewish, and Arabic origins
Associated with widespread tissue involvement
The amyloid fibril proteins are made up of AA proteins, suggesting that this form of amyloidosis is related to the recurrent bouts of inflammation that characterize this disease.
The gene for familial Mediterranean fever has been cloned, and its product is called pyrin; although its exact function is not known, it has been suggested that pyrin is responsible for regulating acute inflammation, presumably by inhibiting the function of neutrophils.
With a mutation in this gene, minor traumas unleash a vigorous, tissue-damaging inflammatory response.
In contrast to familial Mediterranean fever, a group of autosomal dominant familial disorders is characterized by deposition of amyloid predominantly in the peripheral and autonomic nerves.
These familial amyloidotic polyneuropathies have been described in kindreds in different parts of the world, for example, in Portugal, Japan, Sweden, and the US.
Localized Amyloidosis The deposits may produce grossly detectable nodular masses or be evident only on microscopic examination. Nodular (tumor-forming) deposits of amyloid are most often encountered in the lung, larynx, skin, urinary bladder, tongue, and the region about the eye. Frequently, there are infiltrates of lymphocytes and plasma cells in the periphery of these amyloid masses. At least in some cases, the amyloid consists of AL protein and may therefore represent a localized form of immunocyte-derived amyloid.
Endocrine Amyloid Microscopic deposits of localized amyloid may be found in certain endocrine tumors, such as medullary carcinoma of the thyroid gland, islet tumors of the pancreas, pheochromocytomas, undifferentiated carcinomas of the stomach in the islets of Langerhans in patients with type 2 diabetes mellitus.
In these settings, the amyloidogenic proteins seem to be derived either from polypeptide hormones (medullary carcinoma) or from unique proteins (e.g., islet amyloid polypeptide).
Amyloid of Aging Senile systemic amyloidosis refers to the systemic deposition of amyloid in elderly patients (usually in their 70s and 80s).
Because of the dominant involvement and related dysfunction of the heart (typically presenting as a restrictive cardiomyopathy and arrhythmias), this form is also called senile cardiac amyloidosis.
The amyloid in this form is composed of the normal TTR molecule.
In addition, another form predominantly affecting only the heart results from the deposition of a mutant form of TTR.
Approximately 4% of the black population in the United States is a carrier of the mutant allele, and cardiomyopathy has been identified in both homozygous and heterozygous patients
MORPHOLOGY:
In amyloidosis secondary to chronic inflammatory disorders, kidneys, liver, spleen, lymph nodes, adrenals, and thyroid, as well as many other tissues, are typically affected.
Immunocyte-associated amyloidosis more often involves the heart, gastrointestinal tract, respiratory tract, peripheral nerves, skin, and tongue.
The amyloidosis may or may not be apparent on macroscopic examination.
Often small amounts are not recognized until the surface of the cut organ is painted with iodine and sulfuric acid. This yields mahogany brown staining of the amyloid deposits.
When amyloid accumulates in larger amounts, the organ is frequently enlarged and the tissue appears gray with a waxy, firm consistency.
Histologically, the amyloid deposition is always extracellular and begins between cells, often closely adjacent to basement membranes.
As the amyloid accumulates, it encroaches on the cells, in time surrounding and destroying them.
In the immunocyte-associated form, perivascular and vascular localizations are common
The histologic diagnosis of amyloid is based almost entirely on its staining characteristics.
The most commonly used staining technique uses the dye Congo red, which under ordinary light imparts a pink or red color to amyloid deposits. Under polarized light the Congo red-stained amyloid shows so-called apple-green birefringence
. This reaction is shared by all forms of amyloid and is caused by the crossed β-pleated configuration of amyloid fibrils
Confirmation can be obtained by electron microscopy, which reveals amorphous nonoriented thin fibrils.
AA, AL, and ATTR types of amyloid can also be distinguished by specific immunohistochemical staining.
Kidney Amyloidosis of the kidney is the most common and most serious involvement in the disease.
Grossly, the kidney may appear unchanged, or it may be abnormally large, pale, gray, and firm; in long-standing cases, the kidney may be reduced in size.
Microscopically, the amyloid deposits are found principally in the glomeruli, but they are also present in the interstitial peritubular tissue as well as in the walls of the blood vessels.
The glomerulus first develops focal deposits within the mesangial matrix and diffuse or nodular thickenings of the basement membranes of the capillary loops.
With progression, the deposition encroaches on the capillary lumina and eventually leads to total obliteration of the vascular tuft
The interstitial peritubular deposits are frequently associated with the appearance of amorphous pink casts within the tubular lumens, presumably of a proteinaceous nature.
Amyloid deposits may develop in the walls of blood vessels of all sizes, often causing marked vascular narrowing
Spleen Moderate or even marked enlargement(200-800gm).
One of two patterns may develop. The deposits may be virtually limited to the splenic follicles, producing tapioca-like granules on gross examination ("sago spleen"), or the involvement may affect principally the splenic sinuses and eventually extend to the splenic pulp, forming large, sheetlike deposits ("lardaceous spleen"). In both patterns the spleen is firm in consistency, and cut surfaces reveal pale gray, waxy deposits
Liver Massive enlargement (as much as 9000 gm). In such advanced cases the liver is extremely pale, grayish, and waxy on both the external surface and the cut section. Histologically, amyloid deposits first appear in the space of Disse and then progressively enlarge to encroach on the adjacent hepatic parenchyma and sinusoids
The trapped liver cells undergo compression atrophy and are eventually replaced by sheets of amyloid; function may be preserved even in the setting of severe involvement
Heart
Either as isolated organ involvement or as part of a systemic distribution.
When accompanied by systemic involvement, it is usually associated with immunocyte dyscrasias.
The isolated form (senile amyloidosis) is usually confined to older individuals..
The deposits may not be evident on gross examination, or they may cause minimal to moderate cardiac enlargement
The most characteristic gross findings are gray-pink, dewdrop-like subendocardial elevations, particularly evident in the atrial chambers.
On histologic examination, deposits are typically found throughout the myocardium, beginning between myocardial fibers and eventually causing their pressure atrophy
Other Organs Encountered in systemic disease.
The adrenals, thyroid, and pituitary are common sites . In this case also the amyloid deposition begins in relation to stromal and endothelial cells and progressively encroaches on the parenchymal cells.
Surprisingly, large amounts of amyloid may be present in any of these endocrine glands without apparent disturbance of function.
In the gastrointestinal tract, a relatively favored site, amyloid may be found at all levels, sometimes producing tumorous masses that must be distinguished from neoplasms.
Nodular depositions in the tongue may produce macroglossia.
On the basis of the frequent involvement of the gastrointestinal tract in systemic cases, gingival, intestinal, and rectal biopsies serve in the diagnosis of suspected cases.
Deposition of β2-microglobulin amyloid in patients receiving long-term dialysis occurs most commonly in the carpal ligaments of the wrist, resulting in compression of the median nerve (carpal tunnel syndrome
CLINICAL FEATURES
Nonspecific complaints such as weakness, fatigue, and weight loss are the most common initial symptoms. Later by renal disease, hepatomegaly, splenomegaly, or cardiac abnormalities. Renal involvement giving rise to severe proteinuria is often the major cause of symptoms in reactive systemic amyloidosis. Progression of the renal disease may lead to renal failure, which is an important cause of death in amyloidosis..
The hepatosplenomegaly rarely causes significant clinical dysfunction, but it may be the presenting finding.
Cardiac amyloidosis may manifest as conduction disturbances or as restrictive cardiomyopathy Cardiac arrhythmias are an important cause of death in cardiac amyloidosis
The diagnosis of amyloidosis may be suspected from the clinical signs and symptoms and from some of the findings mentioned;
Biopsy and subsequent Congo red staining is the most important tool in the diagnosis of amyloidosis.
In general, biopsy is taken from the organ suspected to be involved. For example, renal biopsy is useful in the presence of urinary abnormalities. Rectal and gingival biopsy specimens contain amyloid in as many as 75% of cases with generalized amyloidosis.
Examination of abdominal fat aspirates stained with Congo red is a simple, low-risk method.
In suspected cases of AL amyloidosis, serum and urinary protein electrophoresis and immunoelectrophoresis should be performed.
Bone marrow aspirate in such cases usually shows plasmacytosis, even if skeletal lesions of multiple myeloma are not present
The outlook for patients with generalized amyloidosis is poor, with the mean survival time after diagnosis ranging from 1 to 3 years.
In AA amyloidosis, the prognosis depends to some extent on the control of the underlying condition. Patients with myeloma-associated amyloidosis have a poorer prognosis, although they may respond to cytotoxic drugs used to treat the underlying disorder.
Resorption of amyloid after treatment of the associated condition has been reported, but this is a rare occurrence.
