renal amyloidosis

Amyloidosis constitutes a heterogeneous group of distinct diseases which differ in their pathogenesis and clinical course.

Amyloid is defined as the deposition of insoluble protein fibrils, forming histologically a homogeneous, extracellular eosinophilic mass.

Congo Red +++ Displays green birefringence under

polarized light

tion

Amyloid fibril protein occurs in tissue deposits as rigid, non-branching fibrils 7-to 10 nm in dm

When analysed by X-ray diffraction, the fibrils exhibit a characteristic cross Beta diffraction pattern

Pentagonal molecule

95% Protein Fibril

5% Glycoprotein P component

A biochemical approach is the basis of the classification.

The current WHO classification is based upon the type of amyloid fibril, referred as Precursor Protein.

Which by convention is designated A and followed by a suffix that is an abbreviated form of the parent or precursor protein name.

For example, when amyloid fibrils are derived from immunoglobulin light chain, the amyloid fibril is AL and the disease is AL amyloidosis.

Similarly when the amyloid fibrils are derived from acute phase reactant- Serum AA protein, the amyloid fibril is AA and the disease is AA amyloidosis.

There are than 20 types of precursor proteins are known associated with various clinical forms of amyloidosis.

They are associated with variety of

-Inflammatory-Immune-Infectious-Hereditary conditions

Amyloid protein Precursor Systemic(S) or Localized (L)

Syndrome

AL/AH Immunoglobulin light/heavy chain

S, L Primary, Myeloma assosiated.

AA Serum AA protein

S Sporadic, secondary, reactive, familial

ATTR Transthyretin S, ? L Familial, Senile, Systemic

AFib Fibrinogen A a chain

S Familial

AApoAI, II, IV Apolipoprotein AI. AII, AIV

S, L Familial, sporadic(aging)

AGEL Gelsolin S Familial

ALys Lysosome S Familial

ACys Cystatin C S Familial

Ab2M B2 Microglobulin S, ? L Dialysis associated

Precursor protein is Immunoglobulin light chain (AL) or a few times heavy chain (AH).

Associated with hepatic, cardiac and GIT involvement.

The most common clinical presentation is proteinuria with or without renal insufficiency

AA amyloidosis arises in the context of an acute phase response seen in inflammatory arthritis, periodic fevers, chronic infections and malignancies.

This protein is derived from acute phase reactant Serum Amyloid A or SAA

Patients of an age range 11 to 87 years (median 55) are affected.

In younger patients a hereditary component must be considered.

Familial Mediterranean fever remains an important cause around mediterranean and in its immigrant population.

Protein urea and nephrotic syndrome are most common presenting symptoms.

Diverse group of autosomal dominant diseases much less frequent than AL or AA amyloidosis.

In keeping with the current classification , these are named after the precursor amyloid fibril protein.

Among these diseases are amyloidosis derived from

1) Fibrinogen A a-chain (Afib)2) Transthyretin (ATTR)3) Apolipoprotein AI (AApoA1)4) Apolipoprotein AII (AApoAII)5) Gelsolin (Agel)6) Lysozyme (Alys)7) Cystatin (Acys)

Dialysis associated amyloidosis (AB2M) is a type of systemic amyloidosis developing in patients undergoing long-term hemodialysis.

The amyloid precursor protein is B2-microglobulin, which is a sub unit of class I histocompatibilty antigens.

The protein is not effectively removed during dialysis.

Clinical manifestation of the disease are zero at 5 years but increase to 50% at 12 years.

There can be Peripheral Osteoarthropathy, Spondyloarthropathy, Ischemic colitis and Heart failure.

• Enlarged kidneys• Pale, waxy appearing cut surfaces• Increase in the weight of kidney

• Amyloid deposits can be found in any of the renal compartments.

• Glomerular amyloid formations begin in the mesangium.

• And then extends to the capillary walls.

In H/E sections, amyloid appears as eosinophilic, amorphous,

hyaline material.

Amyloid deposition in glomeruli may occur in following patterns:

• 1) Segmental.• 2) Diffuse mesangial.• 3) Nodular.• 4) Pure basement membrane pattern

• Early segmental deposits are small and confined to mesangium without creating nodularity

• It is very easy to miss this early form

• In the diffuse form • The mesangium is uniformly expanded by weakly

PAS positive acelluar deposits.

• In the nodular form • Mesangium is asymmetrically expanded by large

masses of amyloid that compress the capillary spaces.

• Rarely cresents can be seenHighlighting the fact that capillary wall rupture has occured

• Renal vessels are often involved with arteriolar deposits being most frequent followed by deposits in arteries, PTCs and veins.

• These deposits may be subtle or may replace the vessel wall completely, occluding the lumen.

• In rare cases vessels walls are the only site for amyliod deposition.

The tubules may show non specific findings.

Interstitial and peri-tubular amyloidosis is seen in 50 %of cases.

Medullay amyloid deposits are more frequent.

A multinucleated giant cell reaction may accompany amyloid deposits.

• Amyloid do not stain by silver staining• Occasionally may stain with silver stains and

show spicules (Jones silver).

• Congo red is the gold standard procedure.• Congo Red-Positive material must polarize and

produce apple green birefringence to be considered diagnostic.

• To demonstrate small amount of amyloid, sections should be cut to a thickness of 9 to 10um.

Thioflavin fluorescence is more sensitive in detecting small amount of amyloid.

Methyl violet and Sulphonated Alcian blue stains are less specific.

Typing of amyloid deposits is important because of the difference in their treatment strategies.

Typing of the amyloid deposits can be performed with various techniques.

The most definitive method used is IF or IHC staining of tissue using antibodies that are directed against known amyloid proteins.

• The typical antibody panel should include • Amyloid P component• Kappa & lambda Ig light chains• Amyloid A protein• Transthyretin• Fibrinogen• Beta-2 microglobulin

• This panel allowed definitive typing of amyloid in 90% of kidney biopsies

Stains for AA and Apolipoprotein AI , AII, may be included depending upon the differential diagnosis.

• Commercial antibodies are raised against the constant regions of the Ig light chains.

• A subset of AL, in which amyloid fibrils are derived from a truncated light chain

“containing only variable regions”

will be nonreactive with commercial antibodies

• Therefore, negative light chain staining does not rule out AL amyloidosis.

• Amyloid is characterized randomly disposed, rigid, nonbranching, variably long, 7-to 10nm-dm fibrils.

Massive expansion of the mesangium by fibrillar deposits.

Subepithelial spikes due to amyloid deposition.

Amyloid infiltration through the basement membrane with resulting feathery spikes with basement membrane material and delicate amyloid fibrils are shown in this case.

Renal amyloidosis was divided into 6 classesSimilar to the classification of SLE

A proposed histopathologic classification

The diagnosis of amyloid can be made with certainty in majority of cases using a combined apprach, including Light microscope, histochemical, and ultrastructural techniques.

It is important to identify the precursor protein using ancillary diagnostic techniques i.e. IF, IHC.

Nodular glomerular amyloidosis can be confused with other nodulat glomerulopathies i.e. ????

Diabetic nephropathy.Light chain deposition

disease.Heavy chain deposition

disease.

Ultrastructural features can differentiate

these entities.

Linear IgG (DM) Kappa light chain pisitivity(LC)

Other infiltrative glomerular processes must be ruled out.

Fibriallary and immunotactoid glomerulopathies may be associated with expanded mesangium and other feature of amyloidosis.

The negative Congo Red stain and ultrastructural finding differentiate these diseases.

The overall prognosis in amyloidosis is poor.

AL amyloidosis has the worst prognosis. Prognosis largely depends on systemic

involvement. Cardiac, hepatic and GIT involvent are

important negative predictor of survival especially in AL amyloidosis.

From management point of view there are three important categories.

AL AMYLOIDOSISManagement is

targeted at the control of underlying plasma

cell dyscrasia.Treatment with high-dose melphalan and

autologous blood stem transplantation has led an improvent in overall

survival.

AA AMYLOIDOSISContol of the acute phase response is currently the

standard of care. Disease-modifying anti-

rheumatic drugs, alkylating agents, anti-

TNF therapies, antibiotics, steroids and surgeries are

being used.

HERIDITORY AMYLOIDOSISSince most of the

abnormal proteins are being produced by liver,

liver transplant is currently being offered to affected

patients. In severe disease, combined liver,

kidney and heart transplant is considered.

Best outcomes have been observed with AA amyloidosis with 92% 5-year survival rate.

In AL amyloidosis the 5-years survical rate is 63%.

In AL amyloidosis the renal transplantation is most clearly indicated for patients without systemic manifestations of Myeloma.

In AA amyloisdosis good control of acute phase response is essential.