Health Human Disease Blog

Amyloidosis is a systemic disease that is clas­sified as either primary (idiopathic) or second­ary—that is, accompanying a chronic inflamma­tory (tuberculosis, leprosy, osteomyelitis), neoplastic (multiple myeloma), or hereditary (familial Mediterranean fever) process. Renal in­volvement is highly prevalent and follows the same course in either form of amyloidosis. Glo­merular, tubular, and vascular deposits of amy­loid occur throughout the kidneys.

The majority of patients are over 50 years of age at the time of diagnosis. The most common renal presentation is that of asymptomatic proteinuria, often with paraproteinuria (e.g., Bence-Jones pro­teinuria). However, about one third of patients have the full nephrotic syndrome. Fanconi’s syn­drome (see above), an indicator of concomitant tubular dysfunction, is not uncommon. Signs of amyloid deposits in other organs, such as ma-croglossia, cardiomyopathy, hepatosplenomegaly, malabsorption, or peripheral neuropathy, may aid in diagnosing the etiology of the glo­merulopathy. A positive rectal biopsy for amyloi­dosis correlated highly with renal involvement. Enlarged kidneys may be found on intravenous urography (IVP) or renal ultrasonography.

Routine light microscopy may show only bland eosinophilic deposits in the mesangium or in cap­illary loops. Special staining by Congo red reveals pink deposits in mesangium, capillary loops, and blood vessel walls; the deposits show green birefringence under polarized light. Immunofluores-cent staining is not helpful. On electron micros­copy. the diagnosis can be established by identification of characteristic, noncollagen fi­brils of 8 to 10 nm deposited randomly or in bun­dles within the mesangium or capillary basement membranes.

A course leading to terminal renal failure is seen in most patients. Asymptomatic proteinuria may persist for some years, but the occurrence of the nephrotic syndrome usually heralds a rapid progression of renal failure. Steroids have no ef­fect on the disease, nor do alkylating agents seem to alter the course. Colchicine therapy appears promising in patients with familial Mediterra­nean fever.