AL Amyloidosis

Slide 1 · AL Amyloidosis

Immunoglobulin light-chain misfolding, systemic deposits and clinicopathologic diagnosis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define AL amyloid and identify its plasma-cell source.

Explain why some monoclonal light chains become extracellular fibrils.

Recognize the shared morphology, organ injury and Congo red reaction.

Integrate tissue amyloid, fibril typing and evidence of a clonal source.

Slide 3 · The defining clinicopathologic question

An adult has progressive proteinuria, cardiac dysfunction and a circulating monoclonal immunoglobulin.

Which finding establishes amyloidosis—and which additional result establishes that it is AL?

A circulating monoclonal protein alone does not identify deposited amyloid.

Slide 4 · Amyloidosis denotes a group, not one protein

Shared finding

Extracellular fibrillar protein deposits

Similar tissue appearance and Congo red behavior

Critical difference

AL: Immunoglobulin light chain

AA: SAA-derived; ATTR: Transthyretin-derived

Slide 5 · What the abbreviation AL denotes

A = amyloid; L = immunoglobulin light chain.

Fibril constituents may be intact light chains, amino-terminal fragments or both.

AL arises from light chains secreted by a monoclonal plasma-cell population.

Slide 6 · A restricted light-chain clone

Clonal plasma-cell population

One preferential Ig light-chain product

Amyloidogenic light-chain precursor

Extracellular AL fibrils

The pathogenic product—not necessarily a bulky tumor—is central to AL disease.

Slide 7 · The light-chain classes: λ and κ

λ (lambda)

Most AL proteins analyzed are λ-derived.

This is a tendency, not a requirement.

κ (kappa)

κ light chains and fragments can also form amyloid.

Typing must determine the actual deposited product.

Slide 8 · Systemic disease begins at a cellular source

Bone marrow plasma-cell clone

Secreted light chain in blood

Misfolding and fibril formation

Deposits in distant organs

AL amyloidosis is usually systemic because its precursor circulates.

Slide 9 · Proteins cross the threshold into aggregation

Soluble light-chain precursor

Unstable or misfolded conformer

Associated oligomers

Insoluble extracellular fibrils

The normal soluble form and the deposited fibril share a protein origin, not a folding state.

Slide 10 · Why a plasma-cell clone matters

Normal plasma cells generate immunoglobulin proteins.

A monoclonal population repeatedly secretes a restricted product.

A disease-specific light-chain sequence can impart a high tendency to misfold.

Even a modest clone may therefore cause severe tissue pathology.

Slide 11 · Monoclonal protein production is not equivalent to amyloid

Monoclonal protein

Identifies a restricted Ig-producing population.

May be found in serum or urine.

Tissue amyloid

Demonstrates extracellular insoluble fibrils.

Must be detected in tissue and then biochemically typed.

Slide 12 · AL often lacks overt multiple myeloma

Most persons with AL amyloid do not have classic multiple myeloma.

Many have a modest increase in marrow plasma cells.

Abnormal protein production may dominate without tumor masses.

“Primary amyloidosis” is the older name, not evidence of a nonclonal disease.

Slide 13 · Myeloma-associated AL is an important subset

Systemic AL amyloidosis to 5%–15% of individuals with multiple myeloma.

Myeloma plasma cells may produce an M protein and free unpaired light chains.

AL pathology depends on the amyloidogenic properties of those light chains.

Slide 14 · A source-based epidemiologic anchor

AL burden in the United States

Approximately 2,000–3,000 new AL cases annually.

Interpret this as a textbook-reported estimate.

Relationship to myeloma

AL in 5%–15% of persons with myeloma.

Most AL patients lack classic myeloma.

Slide 15 · The M-protein spike: What it represents

An M spike reflects abnormal production of a restricted immunoglobulin by plasma cells.

It provides evidence of monoclonality in the appropriate clinical context.

It neither proves a tissue deposit nor assigns that deposit to the AL type.

Slide 16 · Free immunoglobulin light chains

Clonal plasma cell

Free, unpaired κ or λ light chain

Detectable in serum

May pass into urine

Circulating and urinary light chains are part of the clonal-protein investigation.

Slide 17 · Bence Jones protein is a clinical clue

Bence Jones proteins are free, unpaired immunoglobulin light chains.

Their relatively small molecular size permits urinary excretion.

Finding them supports a plasma-cell product—but does not itself establish amyloid deposition.

Slide 18 · Why most free light chains do not become amyloid

Free light chains in myeloma

May be abundant in serum and urine.

Most affected individuals do not develop amyloidosis.

Amyloidogenic light chains

A specific sequence can favor folding instability and aggregation.

Deposition depends on protein quality as well as quantity.

Slide 19 · Amino-acid sequence shapes amyloidogenicity

Distinct light-chain sequence

Intrinsic physicochemical propensity

Misfolding and assembly

Tissue deposition

The source identifies sequence dependence as a principal explanation for why amyloidogenicity varies.

Slide 20 · Protein quality control usually limits deposition

Amyloidogenic precursor

Production / aggregation outpaces clearance

Misfolded protein persists

Extracellular accumulation

Proteasomes and macrophages normally remove misfolded material; Persistence favors deposition.

Slide 21 · Oligomers are precursors to mature fibrils

Misfolded monomers

Soluble oligomers

Larger aggregates

Insoluble fibrils

Progressive self-association converts a soluble precursor into persistent deposits.

Slide 22 · Cross-β structure explains shared staining

Schematic: Stacked β-sheet segments

Amyloid fibrils have a β-pleated organization irrespective of precursor protein.

This common conformation underlies the characteristic Congo red optical reaction.

Slide 23 · Ultrastructure: Nonbranching fibrils

Schematic: Parallel nonbranching fibrils

8–10 nm

Electron microscopy demonstrates continuous, nonbranching fibrils.

Robbins gives an approximate fibril diameter of 8–10 nm.

Ultrastructure identifies amyloid morphology, not its specific precursor.

Slide 24 · Amyloid deposits contain accessory molecules

Fibrils are associated with serum amyloid P component and extracellular matrix constituents.

Proteoglycans and glycosaminoglycans bind to deposits.

Amyloid as approximately 95% fibril protein and 5% SAP/other glycoproteins.

Slide 25 · Systemic versus localized deposition

Systemic AL

Clonal precursor enters the circulation.

Several distant organs may accumulate AL amyloid.

Localized AL-related deposits

A nodular deposit may be confined to one site.

Some localized deposits contain AL and adjacent lymphoplasmacytic infiltrates.

Slide 26 · AL has tendencies, not a diagnostic organ map

Heart

Infiltrative cardiomyopathy

Kidney

Glomerular proteinuria

Gastrointestinal tract

Digestion and absorption

Peripheral nerves

Neuropathic involvement

Tongue and skin

Soft-tissue deposition

Slide 27 · Deposits impair function through tissue architecture

Extracellular fibril accumulation

Compression and distortion

Cellular pressure atrophy

Organ dysfunction

Deposits injure tissues predominantly without eliciting a marked inflammatory response.

Slide 28 · Gross pathology may be surprisingly subtle

Minimal deposits

Tissue can appear unremarkable macroscopically.

Microscopy remains decisive.

Extensive deposits

An organ may enlarge and become gray, firm and waxy.

Gross appearance alone does not establish amyloid type.

Slide 29 · H&E: Amorphous extracellular eosinophilia

Schematic: H&E appearance

Amyloid appears as amorphous, eosinophilic, hyaline material between cells.

The finding is suggestive but is not specific among hyaline extracellular substances.

Slide 30 · Why H&E alone is insufficient

H&E appearance

Pink, amorphous, extracellular material.

Suggestive in the appropriate distribution.

Potential mimics

Collagen and fibrin may also appear hyaline.

Special staining confirms that the material has amyloid properties.

Slide 31 · Congo red under ordinary light

Schematic: Congo red staining

Congo red imparts a pink-to-red hue to amyloid deposits.

The deposited protein still requires proper optical confirmation and subsequent typing.

Slide 32 · Congo red with polarized microscopy

Schematic: Crossed polarizers

Amyloid shows characteristic apple-green (or yellow-green) birefringence after Congo red staining.

This is a property shared by different amyloid proteins.

Slide 33 · Congo red identifies amyloid—not AL

Congo red-positive tissue

Characteristic birefringence

Amyloid is present

Protein-specific typing required

An amyloid-positive specimen does not answer whether the deposit is AL, AA or ATTR.

Slide 34 · Typing determines the precursor protein

Immunohistochemistry

Specific stains can help distinguish AL, AA and TTR amyloid.

Interpret within the clinical and morphologic context.

Mass spectrometry

Protein identification for all amyloid types.

Available in specialized centers.

Slide 35 · Electron microscopy complements Congo red

Light/polarized microscopy

Congo red positivity and birefringence demonstrate the defining optical pattern.

Electron microscopy

Nonoriented, thin, unbranched fibrils provide structural support.

EM does not by itself type the fibril precursor.

Slide 36 · Early glomerular deposition

Schematic: Early glomerular change

Mesangial matrix expansion is an early manifestation.

Uneven thickening of glomerular capillary basement membranes accompanies deposits.

Illustration only — not a glomerular micrograph

Slide 37 · Progressive glomerular destruction

Schematic: Advanced glomerular change

Deposits progressively narrow and distort glomerular capillary loops.

Confluent deposits can nearly obliterate the capillary tuft.

Illustration only — not a glomerular micrograph

Slide 38 · Kidney: Structure explains the proteinuria

Glomerular amyloid

Capillary tuft alteration

Marked protein leakage

Proteinuria / nephrotic syndrome

Continued glomerular destruction may ultimately cause kidney failure and uremia.

Slide 39 · Renal vessels contribute to ischemic injury

Arterial or arteriolar deposits

Vascular lumen narrowing

Reduced perfusion / ischemia

Advanced renal shrinkage

A kidney with amyloidosis need not always be enlarged.

Slide 40 · The myocardial interstitium is a major target

Schematic: Myocardial amyloid infiltration

Muscle-fiber bundles

Deposits between fibers

Amyloid accumulates between cardiac muscle fibers and may begin subendocardially.

Expanded deposits compress myocytes and impair myocardial function.

Schematic — not a histologic specimen

Slide 41 · Subendocardial deposition affects conduction

Subendocardial amyloid

Conduction tissue involvement

Electrical disturbance

Potentially fatal arrhythmia

Cardiac danger is not limited to the mechanical effects of interstitial infiltration.

Slide 42 · Clinical cardiac phenotype

Mechanical consequences

Insidious heart failure; Restrictive cardiomyopathy may develop.

A grossly unremarkable heart does not exclude disease.

Electrical consequences

Conduction abnormalities and arrhythmias.

These may be immediately life-threatening.

Slide 43 · Gastrointestinal disease may be heterogeneous

Stomach and intestinal deposits can cause malabsorption and diarrhea.

Disturbed digestion may accompany extensive infiltration.

Other patients with gastrointestinal deposits can remain asymptomatic.

Slide 44 · Macroglossia is a useful tissue clue

Amyloid deposition in tongue

Increased tissue bulk and stiffness

Macroglossia

Difficulty speaking or swallowing

This clinical sign reflects local extracellular accumulation, not cellular proliferation.

Slide 45 · Peripheral-nerve involvement in the differential

Peripheral nerves are among the sites more often involved in plasma-cell–associated amyloid.

Peripheral and autonomic neuropathy are not unique to AL; Some hereditary ATTR syndromes also affect nerves.

Protein typing is required before attributing a neuropathic phenotype to AL.

Slide 46 · Vascular deposition predisposes to bleeding

Amyloid in vessel walls

Increased vessel fragility

Bleeding after minor trauma

Potentially severe hemorrhage

Clinical bleeding may arise from tissue fragility even without a specific coagulation-factor defect.

Slide 47 · An additional AL-specific bleeding mechanism

AL amyloid deposits

Factor X binding / inactivation

Reduced functional factor X

Bleeding tendency

Factor X inactivation occurs in some AL cases—not universally.

Slide 48 · Histologic confirmation depends on tissue

The disease diagnosis requires demonstration of amyloid in a specimen.

The affected kidney may be biopsied when renal involvement dominates.

Other potential tissues include rectal or gingival biopsies and abdominal fat aspirate.

Slide 49 · Fat aspirate: Interpret a negative result correctly

Positive Congo red finding

Supports a systemic amyloid diagnosis in an appropriate specimen.

The precursor still needs to be typed.

Negative fat aspirate

Does not rule out amyloidosis.

Robbins characterizes the test as specific but insensitive.

Slide 50 · Look for a circulating clonal product

Robbins recommends serum and urine protein electrophoresis and immunoelectrophoresis for suspected AL.

A monoclonal immunoglobulin or free light chain suggests a clonal source.

Interpret protein studies alongside tissue identification, not as a substitute.

Slide 51 · Bone marrow: A small clone can be consequential

Marrow evaluation often reveals monoclonal plasmacytosis in suspected AL.

An overt myeloma phenotype is not required for systemic AL disease.

The plasma-cell burden and burden of organ deposits are distinct clinical dimensions.

Slide 52 · Three linked observations establish the mechanism

Proven tissue amyloid

AL light-chain typing

A matching clonal plasma-cell source

Integrated AL diagnosis

Avoid assigning amyloid type solely from a monoclonal protein detected in blood.

Slide 53 · Plasma-cell clonality does not type the deposit

What clonality answers

Is there a restricted immunoglobulin-producing population?

Source investigation: Serum, urine and marrow.

What amyloid typing answers

Which precursor forms the actual tissue fibrils?

Deposit investigation: Specific tissue-based methods.

Slide 54 · The main biochemical alternatives

Feature

AL

AA

ATTR

Fibril precursor

Ig light chain

SAA-derived

Transthyretin

Typical source

Plasma-cell clone

Inflammatory acute-phase response

Wild-type or variant TTR

Interpretive caution

Clone ≠ tissue typing

Organ site not definitive

Cardiac phenotype overlaps

Slide 55 · Localized AL-related amyloid is a separate pattern

Systemic AL

Circulating light chain reaches multiple organs.

Clinical effects reflect multiorgan deposits.

Localized deposits

Some nodular masses contain AL-derived material.

Local lymphocytes/plasma cells may surround the deposit.

Slide 56 · First application: Kidney–heart presentation

A patient develops nephrotic-range proteinuria and progressive heart failure; Serum studies show a restricted light-chain product.

What is the most defensible next diagnostic sequence?

Prioritize tissue confirmation and amyloid-protein typing rather than naming AL from the serum result.

Slide 57 · Application: Evidence-based resolution

Biopsy an appropriate tissue

Confirm amyloid (Congo red)

Identify the deposited protein

Characterize the plasma-cell clone

Only integrated findings support assigning systemic AL amyloidosis.

Slide 58 · Second application: Amyloid without myeloma

Biopsy-confirmed AL deposits are present, but marrow shows only a modest expansion of monoclonal plasma cells; There is no overt tumor mass.

Does this exclude a pathogenic plasma-cell disorder?

No. A small clone may be clinically defined by its amyloidogenic protein product.

Slide 59 · A nonbulky clone may still cause major disease

AL is driven by the abnormal secreted protein rather than an obligatory mass-forming malignancy.

Organ injury arises where light chains deposit and alter tissue architecture.

A small marrow clone and extensive organ dysfunction are therefore compatible.

Slide 60 · Prognosis follows systemic organ injury

Generalized amyloidosis as potentially life-threatening.

An overall median survival of about 2 years after AL diagnosis.

That number is a textbook summary, not an individualized prognosis or a newly verified contemporary treatment-era estimate.

Slide 61 · Therapeutic logic follows precursor biology

Monoclonal plasma-cell source

Production of amyloidogenic light chain

Ongoing tissue deposition

Source-directed treatment rationale

Improved treatment options for plasma-cell disorders and emerging anti-misfolding approaches, without specifying a regimen here.

Slide 62 · Major diagnostic errors to avoid

Do not equate an M spike or urinary light chain with tissue-proven amyloid.

Do not infer AL from renal or cardiac organ distribution alone.

Do not mistake Congo red positivity for precursor-specific typing.

Do not exclude AL merely because classic myeloma is absent.

Slide 63 · Integrated take-home model

Amyloidogenic plasma-cell clone

Light-chain misfolding

Extracellular AL fibrils

Tissue infiltration and organ failure

Establish the deposit, type the protein and investigate the clonal source.

Slide 64 · Primary reference and interpretation limits

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 6, Amyloidosis, pp. 230–235.

Core AL section begins on p. 231; tissue morphology, diagnosis and clinical effects are described on pp. 233–235.

The supplied Markdown conversion includes interleaved figure text; no original chapter PDF or reusable authentic microscopy asset was supplied.

All microscopic drawings in this lecture are labeled schematics and are not diagnostic photomicrographs.