Clinical Pearls & Morning Reports
Published April 8, 2020
Serum amyloid A protein is an acute-phase reactant that is produced mainly in the liver; its plasma concentration can increase from approximately 0.03 mg per deciliter to 100 to 200 mg per deciliter in the presence of inflammatory diseases. Systemic serum amyloid A (AA) amyloidosis results from tissue deposition of fibrils of serum amyloid A protein. Read the NEJM Case Records of the Massachusetts General Hospital here.
Q: Who is most at risk for AA amyloidosis?
A: AA amyloidosis occurs primarily in patients with chronic inflammatory disorders (e.g., rheumatoid arthritis, juvenile idiopathic arthritis, or inflammatory bowel disease) or chronic infections (e.g., osteomyelitis or tuberculosis); in some patients, the cause is not identified. In recent years, presumably with improved treatments, some of these disorders are now less commonly associated with AA amyloidosis.
Q: How common is kidney involvement in AA amyloidosis?
A: In patients with AA amyloidosis, kidney involvement is nearly universal, typically resulting in reduced kidney function and proteinuria that may be in the nephrotic range. Microscopic hematuria may be present but is not common. Many patients present with advanced chronic kidney disease that may progress rapidly, over a period of months, to end-stage kidney failure. Some patients have proximal tubular dysfunction or nephrogenic diabetes insipidus.
A: There appears to have been an increase over the past decade or two in the fraction of patients with AA amyloidosis who have chronic skin or other soft-tissue infections related to injection-drug use, caused by what is often referred to as “skin popping” or “muscling.” In cases of AA amyloidosis associated with injection-drug use, heroin is the most commonly implicated drug. A specific type of heroin, “black tar,” may be more likely to cause AA amyloidosis than other types.
A: Patients with HIV-associated nephropathy can present with advanced kidney failure and nephrotic-range proteinuria. They often have normal-sized or large kidneys on ultrasonography, and the kidneys are often described as being very “echodense.” The typical finding on histologic analysis of a renal biopsy specimen is focal segmental glomerulosclerosis, commonly with dilated tubules and extensive chronic interstitial nephritis. Acute, immune complex–mediated glomerulonephritis can also occur.