Modern amyloid nomenclature, based on the amyloid fibril proteins, includes 31 types of amyloidosis. Renal involvement is commonly seen in AA, AL, and several other hereditary and acquired amyloidoses. AA amyloidosis, constituting up to 45% of all systemic amyloidosis cases, is associated with wide variety of chronic inflammatory conditions. The precursor protein of the fibrils in AA amyloidosis is an apolipoprotein, called serum amyloid A, and produced in the liver in response to proinflammatory cytokines. AL amyloidosis is actually known to be the most common form of systemic amyloidosis in the Western countries. In this type of amyloidosis the precursor proteins are monoclonal immunoglobulin light chains, produced by plasma cell clone. Clinical diagnosis of AA and AL systemic amyloidosis is based on the presence of proteinuria or nephrotic syndrome and impaired kidney function in patients with extrarenal manifestations. Kidney biopsy is crucial for the diagnostics, and while Congo red staining with examination of Congo-positive material in the polarized light is confirmative for amyloidosis as such, immune staining, helpful to distinguish AA and AL types, guides treatment strategies. In cases when neither AA nor AL amyloidosis are confirmed, one should consider rare types of amyloidosis—ALECT2, AapolA, AFib or ALys.
Part of the book: Amyloid Diseases