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Renal amyloidosis is a glomerulopathy resulting from glomerular deposition of insoluble fibrillar proteins in the mesangium of the glomerulus.
Definition, classification, epidemiology, clinical presentation, diagnosis, and treatment of amyloidosis: see Amyloidosis.
Diagnosis is confirmed by the presence of amyloid protein on immunofluorescence and electron microscopy. Many different types of amyloid protein exist, but the two most common subtypes are AL and AA amyloid:
1) AL amyloidosis is the most common renal amyloidosis. AL amyloidosis is due to clonal proliferation of plasma cells and can be categorized as a monoclonal gammopathy of renal significance (MGRS), as most patients do not meet criteria for multiple myeloma. It results in organized deposits of light chains in the glomerulus. Renal involvement occurs in ~50% of patients with AL amyloidosis and manifests as decreased renal function and proteinuria. Nephrotic syndrome can occur. Hypertension is usually absent, and the kidneys are often enlarged. Renal treatment response is related to the degree of improvement in light chain production from the underlying condition. Proteinuria and renal function improve with successful therapy.
2) AA amyloidosis is a secondary amyloidosis. It develops as a response to chronic inflammatory conditions such as rheumatoid arthritis. Treatment of the underlying condition may lead to reduction of proteinuria, stabilization of renal function, and in some cases even to a reduction in the amount of amyloid deposited in the kidneys.