Pathology
Amyloidosis
Amyloidosis for MBBS and NEET-PG: chemical nature, AL and AA classification, organ involvement and Congo red staining with apple-green birefringence, mapped to NMC codes PA3.1 and PA3.2.
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Amyloidosis
Amyloidosis for MBBS and NEET-PG: chemical nature, AL and AA classification, organ involvement and Congo red staining with apple-green birefringence, mapped to NMC codes PA3.1 and PA3.2.
Amyloidosis is a group of disorders in which an abnormally folded protein is deposited between cells and disrupts organ function. This chapter covers the chemical nature and classification of amyloid, its causes, the organs it targets and the staining features used to identify it in a specimen.
High-yield: Amyloidosis
- Amyloid is an abnormal extracellular protein deposited in a beta-pleated sheet configuration that is resistant to breakdown.
- Congo red stain gives amyloid an apple-green birefringence under polarised light, the diagnostic finding.
- All types of amyloid share a P component and the beta-pleated sheet structure regardless of the precursor protein.
- AL amyloid is derived from immunoglobulin light chains and is associated with multiple myeloma and plasma cell dyscrasias.
- AA amyloid is derived from serum amyloid-associated protein and follows chronic inflammatory conditions such as tuberculosis and rheumatoid arthritis.
- Beta-2 microglobulin amyloid accumulates in patients on long-term haemodialysis.
- Transthyretin amyloid causes familial amyloid polyneuropathy and senile cardiac amyloidosis.
- The kidney is the organ most often and most seriously affected, presenting with nephrotic syndrome.
- Cardiac amyloidosis produces a restrictive cardiomyopathy with a firm, rubbery, enlarged heart.
- Hepatosplenomegaly and macroglossia are recognised clinical clues to systemic amyloidosis.
- Amyloid appears as amorphous, eosinophilic, hyaline extracellular material on routine haematoxylin and eosin staining.
- Rectal or abdominal fat pad biopsy is a simple and useful site for tissue diagnosis of systemic amyloidosis.
- In Alzheimer disease the amyloid is derived from amyloid precursor protein and forms cerebral plaques.
- Amyloid deposition in blood vessel walls causes wall thickening and luminal narrowing that lead to ischaemia.
Types of amyloid and their associations
- **AL:** Immunoglobulin light chains; multiple myeloma and plasma cell dyscrasias.
- **AA:** Serum amyloid-associated protein; chronic inflammation such as TB and rheumatoid arthritis.
- **Beta-2 microglobulin:** Long-term haemodialysis patients.
- **Transthyretin (ATTR):** Familial amyloid polyneuropathy and senile cardiac amyloidosis.
NMC competencies in this chapter
- **PA3.1:** Pathogenesis and pathology of amyloidosis
- **PA3.2:** Identify and describe amyloidosis in a pathology specimen
Frequently Asked Questions
How is amyloid identified on a slide?
Amyloid stains with Congo red and shows a characteristic apple-green birefringence under polarised light, which confirms the diagnosis.
Which organ is worst affected in systemic amyloidosis?
The kidney is affected most often and most seriously, usually presenting as nephrotic syndrome and progressing to renal failure.
What is the difference between AL and AA amyloid?
AL amyloid comes from immunoglobulin light chains and is linked to plasma cell disorders, while AA amyloid comes from serum amyloid-associated protein and follows chronic inflammation.
Why is a fat pad biopsy useful?
Abdominal fat pad aspiration is a simple, low-risk way to obtain tissue that often shows amyloid in systemic disease, avoiding biopsy of a vital organ.
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