Patho - 4th Asessment - Is - 4 Feb 2007

Amyloidosis Dilip K. Das, MBBS, MD, PhD, DSc, FRCPath. Department of Pathology, Faculty of Medicine, Kuwait University

Amyloidosis: Definition • Amyloidosis is a group of diseases in

which one or more organ systems in the body accumulate deposits of abnormal proteins known as amyloid.

• Amyloid: (1) is a pathologic proteinaceous

substance, (2) deposited between the cells in various tissues and organs of the body, in a wide variety of clinical settings and (3) with progressive accumulation, encroaches on and produces pressure atrophy of adjacent cells.

Amyloid: Staining Characteristics

With light microscope and standard tissue stains (H&E), amyloid appears as an amorphous, eosinophilic, hyaline, extracellular substance.

Congo red: Orange red color under ordinary light but when viewed in a polarizing microscope, a characteristic green birefringence is imparted.

Classification of Amyloidosis I. II. III. IV. V.

Immunocyte-derived systemic amyloidosis (AL amyloidosis). Primary amyloidosis. Reactive systemic amyloidosis (AA amyloidosis). Secondary amyloidosis. Hemodialysis –Associated Amyloidosis Heredofamilial amyloidosis. Localized amyloidosis: (A). Endocrine associated, (B). Senile, and (C). Others.

Immunocyte-derived Systemic Amyloidosis •

Found in with 5 to 15% multiple myeloma patients and in patients with B-cell dyscrasias (monoclonal B-cell proliferations). • Amyloid is systemic indistribution (AL type) and derived from Ig light chains (chiefly λ type). • An excess of corresponding light chain is usually present in the blood and secreted in urine as Bence-Jones protein

Organ involvement and its effect: •

Kidney involvement is a major feature and usual cause of death. • Myocardium : refractory heart failure. • Tongue: enlargement interferes with speech. • Esophagus: dysphagia. • Intestine: lesions lead to obstruction, bleeding, and perforation. • Skin: deposits cause purpura. • Nerve: peripheral neuropathy. • The liver, spleen, lungs, and endocrine organs are affected less frequently.

Reactive Systemic Amyloidosis • Common type of generalized (systemic) amyloid disease. • Called secondary amyloidosis because it is secondary (sequel or complication) to associated inflammatory conditions: chronic pulmonary tuberculosis, lepromatous leprosy, chronic oteomyelitis, bronchiectasis, rheumatoid arthritis, and malignant diseases (e.g., clear cell carcinoma of the kidney and Hodgkin’s lymphoma). • The fibrils consists of amyloid A (AA), derived from SAA, which is an apolipoprotein of a high-density lipoprotein and is greatly elevated in the acute-phase reaction. • Amyloid deposits are generally widely distributed, affecting kidney, liver, spleen, lymph nodes and intestine.

Hemodialysis – Associated Amyloidosis • Found in patients on long-term hemodialysis for renal failure. • The deposited material is β2-microglobulun, which is found in high concentration in patient’s serum. • Amyloid deposit is found in synovium, joints, and tendon.

Heredofamilial Amyloidosis • Consist of a large number of syndromes (most of them are extremely rare): e.g. familial amyloid polyneuropathy, and amyloid nephropathy in familial mediterranean fever.

Localized Amyloid Deposits Endocrine associated: •

Amyloid deposits in the stroma of medullary thyroid carcinoma, a Ccell tumor; amyloid is derived from a polypeptide hormone calcitonin. • Amyloid deposits in the stroma of islet cell tumors, particularly those producing insulin (amyloid is produced by proteolysis of insulin or its prohormone).

Senile amyloidosis: •

Deposits are common in the aged (seventies and eighties); found in heart (atria affected more frequently than ventricles) and brain (as senile plaques). • The plaques found in Alzheimers disease is derived from β-amyloid protein (Aβ), derived from a glycoprotein called amyloid precursor protein (APP). Other localized deposits: Microscopic deposits to nodular masses in sites such as lung, larynx, skin, bladder, and tongue. Consist of AL protein in most cases.

Specific Organ Involvement in Amyloid Disease • • • • • • • • • •

Kidney Liver Spleen Heart Lymph nodes Adrenal Thyroid Pituitary Gastrointestinal tract Respiratory tract

Kidney in Amyloidosis Gross: The organ is usually enlarged and pale but a small scarred kidney results in long standing cases due to secondary ischemic changes.

Micro: Amyloid is deposited primarily in the glomeruli. Mesengial deposition and the deposits along basement membrane cause capillary narrowing and distortion of glomerular tuft. The arterioles, and interstitial tissue between the tubules are also affected.

Kidney in Amyloidosis Clinical impact: Renal involvement in amyloidosis is most common and result is nephrotic syndrome, often as the presenting feature. It is the most serious manifestation and major cause of death.

Liver in Amyloidosis Gross: Liver is enlarged, heavy, pale, and firm.

Micro: Amyloid is deposited in the space of Disse between the endothelium and the liver cells, and progressively encroaches on adjacent hepatocytes and sinusoids. The liver cells undergo atrophy. Vascular involvement and Kupffer cell depositions are frequent.

Clinical impact: Liver function is preserved in the presence of marked involvement.

Spleen in Amyloidosis

Gross: Spleen is enlarged and firm. Focal distribution is common. The cut surface shows numerous translucent nodules distributed throughout the red pulp (characteristic appearance, called ‘sago spleen’). A diffuse type is also recognized. Micro: In localized type amyloid is laid down in the walls of the arterioles in the white pulp and subsequently replaces the malpighian bodies. In diffuse type, amyloid is laid down in the walls of the sinuses and tends to spare the follicles. Fusion of early deposits lead to large map-like areas of amyloidosis (lardaceous spleen).

Heart in Amyloidosis Cardiac involvement is the major manifestation of primary amyloidosis. It occurs in multiple myeloma and usually in elderly people. Gross: Heart is enlarged, rigid, and firm. Micro: Begin with focal subendocardial deposition. In due course widespread deposition of amyloid in the walls of blood vessels and in the interstitial tissue surrounding and replacing muscle fibers. Clinical impact: Cardiomegaly with intractable heart failure. Heart block and arrhythmia due to involvement of conduction system are common. Condition mimicking constrictive pericarditis due to rigidity of the muscle.

Diagnosis of Amyloid Disease in Life •

Amyloid may be demonstrated in biopsy material obtained from liver, spleen, kidney, intestine, and bone marrow. Most common site of biopsy is kidney, when renal manfestations are present. • Tissue involved by amyloidosis has a tendency to bleed when subjected to trauma. Biopsy of gingiva and rectal mucosa has advantage over other sites in that, and should hemorrhage occur, it can readily be controlled. • Fine needle aspiration biopsy of the abdominal fat is also an easily followed and extemely useful procedure for detection of systemic amyloidosis. • Appearance in routine stains: With light microscope and standard tissue stains, amyloid appears as an amorphous, eosinophilic, hyaline, extracellular substance. • Appearance by special stain (Congo red): Amyloid stains an orange red color under ordinary light but when the stained slide is viewed in a polarizing microscope, a characteristic green birefringence is imparted. • Other investigations: In immunocyte-associated amyloidosis, serum and urine protein electrophoresis, and immunoelectrophoresis. Bone marrow aspiration for plasmacytosis.

Congo Red Staining of Liver in Amyloidosis

The Nature of Amyloid • Physical Nature: •

•

Electron microscopy: Amyloid material contains two components.

(1) Rigid nonbranching fibrils* (7.5 to 10 nm): Constitute the major component (about 90%) (2) Pentagonal rod shaped sub-unit (P components): Forms 10% of amyloid tissue and is a glycoprotein (variable PAS positive staining). X-ray diffraction analysis: Characteristic β-pleated configuration* in both major subtypes of amyloid.

• Chemical nature: • Peptide mapping analysis of the sequence of amino acids: Of the 15 biochemically distinct forms identified, 3 are major

chemical types of amyloid: (1) Amyloid of light chain origin (AL) from plasma cells, (2) Unique nonimmunoglobulin protein synthesized in the liver (AA), (3) Aβ amyloid in cerebral lesion of Alzheimer disease • *responsible for unique staining and biological properties (e. g., orange red staining under ordinary light and apple green birefringence while examined under polarized light after Congo red staining).

The Nature of Amyloid

Structure of an amyloid fibril

Ultrastructure

Pathogenesis of Amyloidosis •

Amyloid fibrils (AL protein or AA protein) formed in vivo from a variety of polypeptide fragments, derived either from immunoglobulin of plasma cell origin or from other protein (SAA) of hepatocytic origin. • Amyloidogenic proteins (Immunoglobulin light chains or SAA) present in the blood is deposited in various sites following limited proteolysis by the action of monocyte-derived enzymes. • Thus, mononuclear phagocyte system may play a role by taking up immunoglobulins, Ag-Ab complexes, or other proteins and produce necessary polypeptides for formation of amyloid fibrils.

Proposed Scheme of Pathogenesis of Two Major Forms of Amyloid Fibrils

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