SCINTIGRAPHIC QUANTIFICATION AND SERIAL MONITORING OF HUMAN VISCERAL AMYLOID DEPOSITS PROVIDE EVIDENCE FOR TURNOVER AND REGRESSION

Radiolabelled serum amyloid P component scintigraphy provides informat ion on the diagnosis and distribution of amyloid which was not previou sly available. A simple reproducible method for quantifying the uptake of I-123-labelled serum amyloid P component into individual livers, s pleens and kidneys was devised and evaluated in 22 patients with diffe rent types of systemic amyloidosis. Prospective studies in 10 patients were undertaken in order to monitor aspects of the natural history of visceral amyloid deposits. Although measurements of tracer uptake wer e not as discriminating for diagnostic purposes as the opinions of two highly experienced visual observers, the availability of objective sc intigraphic parameters should facilitate interpretation of serum amylo id P component scans in centres unfamiliar with the technique. The fol low-up studies demonstrated several intriguing features of amyloidogen esis. There was very rapid progression of deposits in some individuals with differential rates of accretion in different organs. The single patient with AL amyloidosis treated with cytotoxic drugs showed substa ntial regression of hepatic amyloid deposits whilst his splenic amyloi d increased. His spleen was then removed and further regression of the hepatic amyloid was observed. It is concluded that quantitative serum amyloid P component scintigraphy is a useful method for assessing vis ceral amyloid and that the deposits not only progress at extremely var iable rates, but can evidently also be mobilized. These findings encou rage active therapeutic approaches in the management of amyloidosis.