What Is AA Amyloidosis?
AA amyloidosis, which was earlier known as secondary AA amyloidosis, is a type of systemic amyloidosis that is marked by the protein misfolding and abnormal deposition of fibers composed of an acute-phase reactant protein called the serum amyloid A protein that is predominantly secreted by the liver cells hepatocytes. The concentration of the protein is increased in cases of inflammation. Currently, AA amyloidosis is associated with some rheumatic diseases, such as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and psoriatic arthritis.
What Is Rheumatoid Arthritis Amyloidosis?
Rheumatoid arthritis amyloidosis is a complication associated with severe rheumatoid arthritis. During this condition, abnormal protein forms in the tissues and organs, affecting them. The involved organs are the kidneys, heart, liver, and digestive system. The kidneys are the most affected organ that can lead to kidney dysfunction. The common symptoms are fatigue, swelling, and proteinuria.
What Is the Pathogenesis of AA Amyloidosis?
In AA amyloidosis, the amyloid deposits mainly consist of serum amyloid A protein, a high-density lipoprotein that is an acute phase reactant protein secreted in high quantities during inflammation. The serum protein is produced by the hepatocytes when inflammatory cytokines, such as interleukins and tumor necrosis factor-alpha, stimulate them. There are two isotopes of the serum amyloid A protein: serum amyloid A1 (SAA1) and serum amyloid A2 (SAA2).
Serum amyloid A1 is the main protein responsible for the increase in serum protein levels during an acute inflammatory reaction. Usually, the amyloid protein A serum levels are low, abnormally elevated during acute inflammatory conditions, and are responsible for causing this disorder. If sustained for a longer duration, the abnormal levels of otherwise low serum amyloid protein A level will eventually lead to the development of AA Amyloidosis disorder.
The serum plasma concentration of serum amyloid protein A is three mg per liter in a healthy person, which rises to about 2000 mg per liter or above in chronic inflammatory conditions during an acute phase response. A sustained synthesis of the serum amyloid protein A is then responsible for the creation of amyloid deposits in the extracellular tissue matrix, leading to this disorder. The amyloid fibrils comprise both serum amyloid A protein and serum amyloid P. The amyloid fibrillogenesis also depends on the supply of chains of heparan sulfate and glycosaminoglycans from the extracellular tissue matrix. This process of subsequent production and deposition of serum amyloid protein in various tissues and organs causes toxicity in the tissues along with organ malfunctioning.
What Are the Causes of AA Amyloidosis?
Chronic inflammatory disorders that have the potential to elevate the serum amyloid protein A are responsible for the development of this disorder. The following chronic inflammatory diseases can cause AA Amyloidosis or secondary AA amyloidosis.
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Juvenile arthritis.
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Ankylosing spondylitis.
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Ulcerative colitis.
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Psoriatic arthritis.
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Chronic infections like tuberculosis.
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Chronic osteomyelitis.
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Cystic fibrosis.
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Skin infections are caused by contaminated needles used in drug abuse.
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Renal cell malignant tumor.
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Castleman's disease.
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Foreign body reaction.
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AIDS.
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Granulomatous reactions that are silicon-induced.
What Is the Epidemiology of AA Amyloidosis?
AA Amyloidosis or secondary amyloidosis is a common type of systemic amyloidosis, with the total number of reported cases found predominantly in developing countries worldwide, along with a few European nations. It occurs mostly in the age group of the fourth to sixth decades of life.
What Are the Symptoms of AA Amyloidosis?
The symptoms of amyloidosis vary depending upon the type of chronic inflammatory reaction along with the organ involved. The commonly affected organs include the kidneys, liver, and stomach, with the kidneys being the most frequently involved.
Kidneys-
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An individual undergoing renal tissue involvement in this condition may observe edema in the lower extremities and reduced micturition.
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Sometimes, bubbles are also formed in the urine, causing the formation of frothy urine.
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High cholesterol levels can also be observed because of the increased amyloid protein deposition in the kidneys.
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The amyloid protein starts appearing in the urine of the affected individual.
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This, in turn, leads to decreased serum albumin levels in the blood.
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Severe cases can develop kidney failure and may require dialysis.
Organs, Like Spleen, Liver, and Thyroid Gland-
Splenomegaly and hepatomegaly are other common findings.
Gastrointestinal Tract-
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Diarrhea.
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Constipation.
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Bleeding is associated with gastric involvement in the condition.
Brain-
Neuropathy of the autonomic nervous system and low vascular pressure are also frequently observed symptoms.
Heart-
AA amyloidosis in the cardiovascular system may lead to congestive heart failure or irregular heartbeat development.
Prodromal Symptoms-
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Fever, malaise, weakness, and headache are other prodromal symptoms associated with the disorder.
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Weight loss is observed in some cases.
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There can be a loss of appetite also.
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Nausea and vomiting can also be seen in the affected individuals.
What Are the Diagnostic Methods for AA Amyloidosis?
Tissue or Organ Biopsy- A biopsy is the gold standard of the diagnostic tests used to identify the disorder. Generally, the doctor advises either:
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Biopsy- Biopsy of the involved tissue by aspirating a small subcutaneous abdominal fat sample under the skin. This is a safe procedure and is very technique-sensitive.
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Organ Biopsy- It can also be performed by taking out a small tissue from the organ involved.
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Amyloidosis- The diagnosis of amyloidosis is confirmed by histological staining of the amyloid protein deposits in the tissues.
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Congo Red Staining- It is considered the most standard dye to identify the amyloid deposits because of the classic apple-green birefringence demonstrated by the amyloid proteins when observed under a polarizing microscope. This is used to differentiate it from other types of proteins.
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Immunohistochemical Staining- This can be done to differentiate among other varieties of systemic amyloidosis, such as AL amyloidosis or heredity-related amyloidosis.
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Urine Tests- To check for kidney involvement.
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Serum Tests- The presence of light-chain immunoglobulins can also be performed to rule out the diagnosis of immunoglobulin-type amyloidosis.
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Genetic Tests- This can also be carried out for the hereditary types of amyloidosis.
What Is the Treatment of AA Amyloidosis?
There is currently no specific treatment available for systemic AA amyloidosis. The healthcare professional aims to treat the underlying chronic inflammatory condition to cure the disorder's symptoms.
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Drug Therapy- Nonsteroidal anti-inflammatory drugs and immunosuppressive agents treat the inflammatory condition.
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Novel Therapeutic Agents- Many novel therapeutic lab-designed antibodies are being developed to target the amyloid fibrils deposited in the tissues.
Conclusion
AA amyloidosis is a severe disorder that can occur as a result of many common inflammatory conditions. The healthcare practitioner can cure the condition by eliminating the underlying pathology. More research is being carried out to develop newer novel drug therapies for treating and managing the disease, more specifically.