A. Brad Farris, III, MD

The classic appearance of amyloid deposits is a pale amorphous accumulation in the mesangium image and along the GBM image in PAS stains without cellular proliferation or inflammation.

EM reveals subepithelial “spicular” amyloid fibrils image in the GBM. Fibrils are ˜ 7-12 nm in diameter and are nonperiodic. Podocytes have effaced foot processes and reabsorption droplets image.



  • Protein folding diseases characterized by accumulation of 7-12 nm diameter fibrils with a β-pleated sheet structure that confers birefringence after staining with Congo red


Amyloidogenic Proteins

  • > 20 different precursor proteins

    • Clonal proliferation of plasma cells (AL/AH types)

    • Chronic inflammation (AA type)

    • Genetic (multiple proteins)

    • Failure of excretion (β2-microglobulin)

    • Neoplasm (e.g., calcitonin)

  • ˜ 90% of renal amyloidosis cases are AL or AA


  • Amyloidogenic proteins have an antiparallel, β-pleated sheet tertiary structure, accounting for Congo red staining and apple-green birefringence under polarized light

    • Resistance to metabolic processing leads to accumulation and interference with physiologic functioning

  • Amyloid deposits composed of amyloidogenic protein and nonfibrillary glycoproteins serum amyloid P (SAP), apolipoprotein E, and glycosaminoglycans

    • SAP (also known as amyloid P component)

      • Normal plasma protein that binds all amyloid proteins

      • SAP present early and promotes deposits

      • Labeled SAP used to image amyloid in vivo

Renal Deposits

  • Certain forms typically involve the kidney (AL, AA, fibrinogen, Apo AI and AII, Alys)

  • Glomerular mesangial amyloid accumulation often occurs 1st as mesangial cells lose usual smooth muscle phenotype and acquire macrophage phenotype

    • Mesangial cells engage in endocytosis and deliver amyloidogenic light chains to lysosomal compartment, where fibril formation takes place

  • Fibrils penetrate and aggregate in the GBM, suggesting that they may be locally formed

AL Amyloid

  • Most common cause of renal amyloidosis in the USA/Western hemisphere

  • Plasma cell dyscrasias or lymphoproliferative disorders

    • Only ˜ 20% meet diagnostic criteria for multiple myeloma or B-cell leukemia/lymphoma when AL amyloidosis is diagnosed

      • Some B-cell neoplasms not identified until ≥ 15 years after AL amyloidosis diagnosis

  • ˜ 75% lambda light chains

    • Often from N-terminal fragment of variable light chain region

  • 40% develop nephrotic syndrome

    • ˜ 10% of AL patients lack glomerular deposits

  • Formerly called primary amyloidosis

AH Amyloid

  • Rare cases of AH amyloid composed of monoclonal Ig heavy chains

    • Can produce nephrotic syndrome

AA Amyloid

  • Most common cause of amyloidosis in underdeveloped countries

    • Becoming less common in developed countries

  • Derived from proteolytic cleavage of serum amyloid A (SAA) protein, an acute phase reactant

  • Associated with chronic inflammatory conditions

    • Infections: Tuberculosis, osteomyelitis, bronchiectasis, decubitus ulcers, skin infections of drug abuse

    • Autoimmune disease: Rheumatoid arthritis, inflammatory bowel disease

    • Genetic syndromes: Familial Mediterranean fever (FMF), MEFV gene (pyrin)

  • 90% have nephrotic syndrome or renal insufficiency at diagnosis

  • Formerly called secondary amyloidosis

ATTR (Transthyretin Amyloidosis)

  • Composed of transthyretin, also known as prealbumin

  • 85% of familial forms of amyloidosis


  • Most common genetic form that affects glomerulus

  • 5% of familial forms


  • Associated with long-term dialysis

  • May cause carpal tunnel syndrome, bone cysts, and joint disease

Leukocyte Chemotactic Factor 2 (LECT2)

  • ˜ 2.4% of renal amyloidosis cases

  • No mutation identified

Other Amyloid Types Affecting Kidney

  • Cystatin C, gelsolin, apolipoprotein AI or AII, lysozyme



  • Incidence

    • 1.4/100,000 per person-year; all types (France)

    • 0.6-1.0/100,000 per person-year; AL type (Minnesota)

    • About 10% of cases are familial

  • Age

    • AL and AA amyloid: Typically 50-70 years old

    • Familial forms: < 40 years old; AFib older

  • Gender

    • M:F = 2:1 overall


  • Proteinuria

    • Present in virtually all with renal involvement

    • ˜ 5% of adult cases of nephrotic syndrome

  • Hematuria

    • Rarely a presenting feature

  • Extrarenal manifestations

    • Congestive heart failure, arrhythmias

    • Dysesthesias

      • Bladder dysfunction

    • Orthostatic hypotension

    • Hepatomegaly/splenomegaly

    • Macroglossia

    • Carpal tunnel syndrome

Laboratory Tests

  • In > 90% of AL amyloidosis patients, monoclonal Ig can be found in blood or urine

    • Most remaining patients have abnormal monoclonal bone marrow plasma cell populations


  • Treat underlying disease

    • Myeloma

      • Alkylating agents (e.g., melphalan) may ↑ survival from 1 year to > 5 years

      • Bortezomib

      • Bone marrow transplantation

    • Inflammatory condition (e.g., immunosuppressive agents for rheumatoid arthritis)

      • Useful for AA amyloidosis

      • Colchicine useful for FMF but not as useful for other causes of AA amyloidosis

  • Transplantation

    • Recurs post transplant (10-20%); graft failure in 33%

    • Outcome can be good in selected patients

      • AL in nonmyeloma patients without severe extrarenal disease


  • Variable but generally poor

  • Median survival: 2 years (Mayo series, 859 patients)


General Features

  • Enlarged, pale, firm, and with a “waxy” appearance

  • Cut surfaces remain firm and flat in contrast to a normal kidney, which bulges after sectioning

  • Lugol iodine stains glomeruli dark brown in cut surfaces (like starch)


Histologic Features

  • Glomeruli

    • Expansion of mesangium and thickening of capillary walls by amorphous eosinophilic material

      • Amorphous deposits are acidophilic, “salmon orange”

      • Usually less acidophilic than collagen (i.e., mesangial sclerosis, interstitial fibrosis)

      • Normal mesangial matrix, presumably destroyed by activated metalloproteinases, is replaced by amyloid fibrils

      • Nodular mesangial expansion can often be seen

      • Amyloid is weakly PAS positive, less than GBM

    • Silver stains: Expanded mesangial areas but ↓ or no silver staining (i.e., “loss of argyrophilia”)

      • GBMs also may be engulfed by the material, showing up as areas of complete GBM discontinuity

      • Subepithelial spikes in capillary loops (“cock’s comb”)

    • Amyloid deposition can 1st be seen in mesangium and blood vessel walls

      • Early mesangial deposits may be quite small and subject to being overlooked, resulting in erroneous diagnosis of minimal change disease/glomerulopathy

    • Little or no hypercellularity

    • Eventually, ESRD kidneys with glomerulosclerosis from amyloid can be suspected by pale staining on JMS or PAS stains

      • Mesangial and subendothelial deposits eventually obliterate glomeruli

    • Rare cases of AL and AA amyloid crescents

    • Trichrome stains blue in amyloid, usually paler than trichrome staining of collagen

  • Tubulointerstitium

    • Congo red staining useful in identifying vascular and interstitial amyloid

      • Helps distinguish from interstitial fibrosis (IF)

    • Interstitial involvement often contiguous with involvement of TBMs and vessels

      • Eventually, IF and tubular atrophy (TA) may be extensive, admixed with interstitial inflammation

    • Tubular casts containing amyloid are sometimes present and, in rare case reports, are the only manifestation of amyloidosis

      • Material has fibrillar appearance characteristic of amyloid on EM

    • Interstitium may be expanded by amyloid material

      • Mast cells may lead to IF in AA type

  • Blood vessels

    • Any vessel can be involved, including vasa recta of renal medulla

    • Blood vessel amyloid can look like hyalinosis

      • Congo red staining helps distinguish amyloid deposition from hyalinosis

    • Interlobular arteries and hilar arterioles are most commonly involved (> 95% of renal biopsies having glomerular involvement)



  • Pattern depends on type of amyloid

    • Deposits variably present in glomerular mesangium, GBM, interstitium, and vessels

    • AL: Single light chain predominates

    • AA: Neither or both light chains stain

    • Fibrinogen (Aα chain) only glomerular

  • Kappa and lambda staining performed on all native renal biopsies, identifying most cases of AL amyloidosis

    • Positive stain is when 1 light chain clearly predominates

      • Light chains may be present in other forms of amyloidosis due to nonspecific trapping

    • Negative stains do not exclude AL amyloid

      • Staining may be negative if light chain is truncated

    • Variants

      • Rare cases stain for an immunoglobulin heavy chain but not for light chains (AH amyloidosis)

      • Rare cases have 1 heavy chain (typically gamma) and 1 light chain (AL/AH amyloid)

Electron Microscopy

  • Fibrils

    • Nonbranching, nonperiodic, ˜ 7-12 nm in diameter

      • Accurate measurement necessary

      • Internal references: Cell membrane 8.5 nm; actin: 5 nm

      • Amorphous “cottony” appearance at ˜ 5,000x

      • Electron-lucent core at ˜ 100,000x

    • Randomly distributed in mesangium and GBM

    • Fibrils sometimes extend transmurally, replacing entire glomerular basement membrane

      • In subepithelial zone, fibrils align roughly perpendicular to GBM, producing “spike” formation or “cock’s comb” (also called “spicular amyloid”)

  • Podocyte foot processes often effaced, and cytoplasm has condensation of actin filaments

Detection of Amyloid

Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Amyloidosis

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