Amyloidosis refers to the deposition of extracellular fibril in tissues. Fibrils, composed of low molecular weight subunits (5 to 25 kD), can organize into a beta-pleated sheet configuration that can deposit in various organs and cause pathology.1 Multiple different precursor proteins have been shown to transform to a fibrillar configuration associated with amyloidosis.
Amyloid deposition can occur in a number of sites, including the kidneys, heart, and liver.1 The specific clinical manifestations depend on the distribution of amyloid deposition. Some clinical and laboratory features that could suggest amyloidosis include a history of easy bruising, waxy skin, presence of muscular hypertrophy, symptoms and signs of heart failure, cardiac conduction abnormalities, hepatomegaly, marked proteinuria, peripheral neuropathy, and coagulopathy.2
Amyloid A (AA) amyloidosis, or secondary amyloidosis, results from the extracellular tissue deposition of serum amyloid A (SAA) protein fibrillar sheets. SAA is an acute phase reactant thought to increase the affinity of high-density lipoproteins (HDL) for macrophages and adipocytes during the acute inflammatory response.3
AA amyloidosis is associated with several chronic inflammatory conditions, including rheumatoid arthritis, juvenile chronic polyarthritis, ankylosing spondylitis, and inflammatory bowel disease.3 Although it is much more common in patients with rheumatoid arthritis, there have been multiple reports of patients with AS presenting with subclinical AA amyloidosis or symptomatic AA amyloidosis.4
The kidney is the most commonly affected organ in AA amyloidosis.1 Deposition of amyloid into the glomerulus can lead to nephrotic syndrome1, leading to symptoms such as heavy proteinuria and generalized edema, which the patient in this case demonstrates. Other complications of nephrotic syndrome include hyperlipidemia and hypercoagulability.