Diagnosis: Amyloidosis
• The major causes of fibrillar deposits in the kidney are amyloidosis, fibrillary glomerulonephritis, and immunotactoid glomerulopathy.
• The mean diameter of amyloid fibrils is 10 nm (range, 8 to 12 nm).
• The mean diameter of the fibrillar deposits in fibrillary glomerulonephritis is 20 nm (range, 16 to 24 nm). In immunotactoid glomerulopathy, the deposits form larger microtubules with a hollow core and mean diameter of 40 nm (range, 30 to 60 nm).
• Additional, rare causes of glomerular fibrillar deposits include fibronectin glomerulopathy and collagenofibrotic glomerulopathy. Mesangial fibrils may also be seen in some cases of diabetic glomerulosclerosis.
• Amyloidoses are classified according to the major type of protein in the deposits. The most common form of renal amyloidosis seen in the United States and most developed countries is primary amyloidosis, also known as light chain (AL) amyloidosis. AL amyloidosis is associated with plasma cell dyscrasias including multiple myeloma. The amyloid precursor protein is a monoclonal light chain.
• Secondary amyloidosis is derived from serum amyloid A (SAA), an acute phase reactant protein synthesized by the liver. Secondary amyloidosis develops in patients with chronic inflammatory disorders of autoimmune or infectious etiology. Associated underlying conditions include rheumatoid arthritis (most common), psoriasis, ankylosing spondylitis, tuberculosis, Crohn disease, chronic draining infections (i.e., chronic osteomyelitis, bronchiectasis), intravenous drug abuse with skin popping, and familial Mediterranean fever.
