AA amyloidosis is a form of
amyloidosis, a disease characterized by the abnormal deposition of fibers of insoluble protein in the extracellular space of various tissues and organs. In AA amyloidosis, the deposited protein is
serum amyloid A protein (SAA), an
acute-phase protein which is normally soluble and whose plasma concentration is highest during
inflammation.[1]
Causes
AA amyloidosis is a complication of a number of inflammatory diseases and infections,[2] although only a small portion of patients with these conditions will go on to develop AA amyloidosis. The most common presentation of AA amyloidosis is renal in nature, including proteinuria, nephrotic syndrome and progressive development of
chronic kidney disease leading to
end stage kidney disease (ESKD) and need for renal replacement therapy (e.g.
dialysis or kidney transplantation).[3] A natural history study of AA amyloidosis patients reported a number of conditions associated with AA amyloidosis:[1]
Signs and symptoms of amyloidosis can vary depending on the affected organ. AA amyloidosis is commonly found in organs like the kidneys, liver, and stomach. If the kidneys are affected, an individual may see swelling in the legs, reduced urination, and at times excessive bubbles in the urine. Amyloid proteins in the kidneys can also lead to high cholesterol.[13] Other organs like the stomach may result in bleeding, constipation, etc.[14]
Pathology
In a healthy individual, the median plasma concentration of SAA is 3 mg per liter.[15] This can increase to over 2000 mg per liter during an acute phase response and a sustained overproduction of SAA is required for the creation of the AA deposits that define AA amyloidosis.[16] High levels of SAA, however, is not a sufficient condition for the development of systemic AA amyloidosis and it remains unclear what triggers the accumulation of AA.[17]
The AA protein is mainly deposited in the liver, spleen and kidney, and AA amyloidosis can lead to nephrotic syndrome and ESRD.[18][19] Natural history studies show, however, that it is the kidney involvement that drives the progression of the disease. In general, old age, reduced serum albumin concentration, end stage kidney failure, and sustained elevated SAA concentration are all associated with poor prognosis.[20]
Diagnosis
Tissue biopsy using subcutaneous abdominal fat tissue aspiration is typically used as it is safe and sensitive. It is also possible to biopsy the rectal mucosa or minor salivary glands. Amyloidosis is confirmed by histological identification of amyloid deposits. At this point, amyloid typing with immunochemical staining is necessary, as the differential diagnosis includes AA amyloidosis,
AL amyloidosis,
hereditary amyloidosis,
dialysis-related amyloidosis and
age-related systemic amyloidosis. Testing of serum and urine for monoclonal immunoglobulins and of serum for free light chains may help rule out immunoglobulin light chain amyloidosis, while
genetic testing may be used if hereditary amyloidosis is suspected.[21]
Treatment
There are currently no approved treatments for systemic AA amyloidosis.[18] The current standard of care includes treatments for the underlying inflammatory disease with anti-inflammatory drugs, immunosuppressive agents or
biologics. AA amyloidosis patients are also receiving treatments to slow down the decline of their renal function, such as
angiotensin II receptor blockers or
angiotensin converting enzyme inhibitors.[22]
Transmission
There is evidence that eating amyloid fibers may lead to amyloidosis. This evidence is based on studies in cattle, chickens, mice, and cheetahs.[23] Thus, in a sense, SAA amyloidosis may be considered a contagious disease, although whether this occurs or is important in the development of naturally occurring amyloidosis remains unknown. Nevertheless, because amyloid fibers can be detected in muscle in low amounts, it raises some concern about whether people could develop amyloidosis as a result of ingesting meat from an animal with the disease.[23]
^Ben Abdelghani K, Mahfoudhi M, Hriz A, El Kossai I, Khefifi A, Turki S, et al. (May 2010). "[AA amyloidosis complicating sarcoidosis: two cases and literature review]". La Revue de medecine interne. 31 (5): 369–71.
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abcdefghijkBharati J, Lahoud OB, Jhaveri KD, Izzedine H (31 May 2023). "AA amyloidosis associated with cancers". Nephrology, Dialysis, Transplantation. 38 (6): 1366–1374.
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^Kanat O, Evrensel T, Filiz G, Usta M, Baskan E, Dilek K, et al. (November 2003). "Systemic AA amyloidosis and nephrotic syndrome associated with small cell carcinoma of the bladder". Nephrology, Dialysis, Transplantation. 18 (11): 2453–4.
doi:
10.1093/ndt/gfg391.
PMID14551390.
^Emekli U, Tümerdem B, Demiryont M (2002). "Rupture of a silicone gel mammary prosthesis and amyloidosis: a case report". Aesthetic Plastic Surgery. 26 (5): 383–387.
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10.1007/s00266-002-2022-x.
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^Goldman AB, Bansal M (March 1996). "Amyloidosis and silicone synovitis: updated classification, updated pathophysiology, and synovial articular abnormalities". Radiologic Clinics of North America. 34 (2): 375–94, xi.
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^Fernández-Nebro A, Tomero E, Ortiz-Santamaría V, Castro MC, Olivé A, de Haro M, et al. (May 2005). "Treatment of rheumatic inflammatory disease in 25 patients with secondary amyloidosis using tumor necrosis factor alpha antagonists". The American Journal of Medicine. 118 (5): 552–556.
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10.1016/j.amjmed.2005.01.028.
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