Definition
• Rare disease linked to the deposition of plaques consisting of amyloid A protein in the tissues.
• Secondary to chronic inflammation.
Epidemiology
• AA amyloidosis is the 3rd variety of amyloidosis (in frequency) in the world and accounts for approximately 10% of all amyloidosis.
• Rare disease < 10 cases / million inhabitants / year.
• Around 400 to 600 cases in France.
• Affects both men and women.
Pathophysiology
There are different types of amyloidosis. AA amyloidosis is also called inflammatory amyloidosis because it is linked to the deposition of a protein involved in inflammation: serum amyloid A (SAA) protein.
In the event of prolonged inflammation, the SAA will be present in excess, will accumulate and be deposited by forming amyloid deposits in various organs such as the kidney, the digestive system, and thus causing dysfunction of the affected organs.
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In France, the diseases most often complicated by AA amyloidosis are: chronic inflammatory arthritis (rheumatoid arthritis, spondyloarthritis, psoriatic arthritis), chronic infections (tuberculosis, bronchial dilation), chronic inflammatory bowel disease (Crohn's disease, ulcerative colitis), and auto-inflammatory diseases including familial Mediterranean fever and finally obesity.
Clinical
There seems to exist during AA amyloidosis a so-called pre-clinical phase during which amyloid deposits can be detected within the organs but without clinical signs or symptoms. There are few specific signs, which makes it difficult to evoke it in the context of a chronic disease and may be the cause of a diagnostic delay.
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Kidney damage:
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This is the most common condition in AA amyloidosis.
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It most often causes edema of the lower limbs, proteinuria (loss of protein in the urine), and/or renal failure (increased blood creatinine).
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Digestive involvement: almost always present, but not always responsible for symptoms. It can be responsible for diarrhea, weight loss, lack of appetite.
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Liver damage: This can cause an increase in liver size and liver enzymes.
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Other organs can be affected: the thyroid, the bladder, the adrenal glands.
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Cardiac involvement is very rare.
Diagnostic
The diagnosis of AA amyloidosis is based on the demonstration of amyloid deposits in pathology on a biopsy. A special coloring makes it possible to recognize these deposits: Congo Red which will give a green-yellow birefringence in polarized light.
It is thanks to the biopsy that the type of amyloidosis (AA, AL or others) can be characterized via specific immunomarkings.
Several biopsy sites can be targeted for diagnosis: biopsy of accessory salivary glands, biopsy of subcutaneous fat, rectal biopsy, renal biopsy (> 90% positivity in AA amyloidosis).
A blood sample is also taken to measure the inflammation by measuring C-reactive protein and SAA protein).
Treatment
The treatment can be discussed in an expert reference center for AA amyloidosis given the rarity of this disease and the complexity of its management.
It groups :
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the so-called etiological treatment, that is to say of the disease responsible for the chronic inflammation. It allows the stabilization or even the regression of amyloidosis.
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replacement therapy in the event of dysfunction of an organ, in particular the kidney: dialysis or kidney transplant.
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There is no specific treatment for AA amyloidosis to date.