Amyloidosis
The kidney is often affected in amyloidosis. Presentation is with asymptomatic proteinuria, nephrotic syndrome or renal failure.
On light microscopy, eosinophilic deposits are seen in the mesangium, capillary loops and arteriolar walls. Staining with Congo red renders these deposits pink and they show green birefringence under polarized light. Immunofluorescence is unhelpful, but on electron microscopy the characteristic fibrils of amyloid can be seen. Amyloid consisting of immunoglobulin light chains (AL amyloid) can be distinguished from the protein found in secondary amyloid (amyloid protein A, AA amyloid). AL amyloid is found in disorders associated with lymphoproliferative diseases such as myeloma, Waldenström's macroglobulinaemia or non-Hodgkin's lymphoma. It is also present in cases of so-called primary amyloidosis where an abnormal clone of cells is presumed to be responsible, although at present not identifiable. AA amyloid is found following long-standing inflammatory conditions such as suppurative infections, rheumatoid arthritis and familial Mediterranean fever.
Diagnosis and Treatment of Amyloidosis
The diagnosis can often be made clinically when features of amyloidosis are present elsewhere. On imaging, the kidneys are often large. Renal biopsy is necessary in doubtful cases.
Treatment of the underlying cause should be undertaken. In primary amyloid, treatment also used in myeloma such as corticosteroids and melphalan and bone marrow transplantation may be of benefit. The success of dialysis and kidney transplantation is dependent upon the extent of amyloid deposition in extrarenal sites, especially the heart.
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