# Amyloidosis

> Amyloidosis for NEET-PG: AL, AA and ATTR types, Congo red apple-green birefringence, organ involvement and the diagnostic approach.

- Canonical URL: https://prepelephant.com/topics/neet-pg/pathology/amyloidosis
- Exam / course: NEET-PG · Subject: Pathology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Amyloidosis", PrepElephant, https://prepelephant.com/topics/neet-pg/pathology/amyloidosis

## Direct answer

Amyloidosis is a group of disorders in which misfolded proteins deposit extracellularly as beta-pleated sheet fibrils that stain characteristically with Congo red, showing apple-green birefringence under polarised light. The systemic forms that matter for NEET-PG are AL (primary, from monoclonal light chains), AA (secondary, from the acute-phase protein serum amyloid A in chronic inflammation) and ATTR (from transthyretin, in senile and hereditary forms), each with its own precursor, organ preference and signature.

## What you must remember

- **Diagnosis by staining:** amyloid is homogenous and eosinophilic on H&E, but Congo red with polarised apple-green birefringence is diagnostic; all fibrils share the serum amyloid P component.
- **AL (primary) amyloidosis:** lambda light chains from a plasma cell dyscrasia; the commonest systemic form; targets kidney (nephrotic syndrome), heart (restrictive cardiomyopathy), nerves and liver; periorbital purpura and macroglossia are classic clues.
- **AA (secondary) amyloidosis:** serum amyloid A deposited in chronic inflammation — rheumatoid arthritis, inflammatory bowel disease, chronic osteomyelitis, tuberculosis, bronchiectasis (leading causes in India); kidneys, liver and spleen are favoured, renal involvement dominating.
- **ATTR amyloidosis:** wild-type transthyretin in elderly men causing senile cardiac amyloid, often with carpal tunnel syndrome; hereditary variants carry point mutations such as Val30Met.
- **Dialysis-associated amyloidosis:** beta-2 microglobulin depositing in joints and carpal tunnels in long-term dialysis patients.
- **Localised amyloid:** medullary thyroid carcinoma stroma (procalcitonin-derived), islet amylin in type 2 diabetes, and cerebral amyloid in Alzheimer plaques and angiopathy.
- **Diagnostic route:** biopsy of abdominal fat pad, rectum or gingiva with Congo red staining; serum free light chains and immunofixation for AL; cardiac imaging for cardiac involvement.

## Common confusion

AL versus AA generates the recurring confusion: AL arises from a plasma cell disorder and must be sought with serum and urine electrophoresis and free light chains, while AA complicates chronic inflammatory disease and is treated by controlling that disease — the precursor, not the deposit, defines the work-up. Students also mix organ preferences: cardiac involvement points to AL or ATTR, whereas AA characteristically spares the heart. The terms primary and secondary are historical — modern classification names the precursor protein (A plus the protein name), the language current exams prefer.

## Exam-focused takeaway

NEET-PG stems on amyloidosis are recognition questions: the stain and its apple-green birefringence identify the deposit; the clinical setting names the type — nephrotic syndrome with a monoclonal band (AL), chronic tuberculosis or rheumatoid arthritis with renal amyloid (AA), senile heart failure (ATTR), or long-term dialysis with carpal tunnel (beta-2 microglobulin). Expect one-liners on amyloid P component, beta-pleated sheet structure, macroglossia and periorbital purpura, and biopsy site choice. Learn each type as precursor, cause and target organ — a compact grid worth full marks.

## Frequently asked questions

### What is amyloid and how is it diagnosed histologically?

Extracellular deposits of misfolded protein fibrils in a beta-pleated sheet conformation, stained orange-red by Congo red and showing apple-green birefringence under polarised light.

### What is the difference between AL and AA amyloidosis?

AL comes from monoclonal light chains in plasma cell disorders; AA from serum amyloid A raised in chronic inflammation such as tuberculosis, rheumatoid arthritis or inflammatory bowel disease.

### Which organs are affected in systemic amyloidosis?

Kidneys (nephrotic syndrome), heart (restrictive cardiomyopathy and conduction disease), liver, spleen, nerves, and soft tissues producing macroglossia and periorbital purpura, chiefly in AL.

### What is ATTR amyloidosis?

Amyloid derived from transthyretin — wild-type causing senile cardiac and carpal tunnel amyloid in elderly men, and mutant hereditary forms causing familial amyloid polyneuropathy.

### Which biopsy site is used to diagnose systemic amyloidosis?

Abdominal fat pad aspiration is the usual first choice, being simple and sensitive; rectal or gingival biopsies are alternatives, all Congo red confirmed.

### Where does amyloid appear in endocrine disease?

Calcitonin-derived amyloid in the stroma of medullary thyroid carcinoma and islet amyloid (amylin) in the pancreas of type 2 diabetes are the classic localised endocrine deposits.