PROSPECTIVE AND SERIAL STUDY OF PRIMARY AMYLOIDOSIS WITH SERUM AMYLOID-P COMPONENT SCINTIGRAPHY - FROM DIAGNOSIS TO PROGNOSIS

OBJECTIVE: The purpose of this study was to assess the value of the se rum amyloid P (SAP) component scintigraphy in patients with primary am yloidosis (AL). MATERIAL AND METHODS: Pure human SAP labeled with iodi ne-123 (I-123-SAP) was given intravenously to 24 patients with biopsy- proven systemic amyloidosis (15 without multiple myeloma = group 1, an d 9 with multiple myeloma = group 2) and to 6 patients with multiple m yeloma without any clinical or biological signs of amyloidosis (group 3). Whole-body images as well as regional views and tissue retention l evels were obtained after 24 hours. Our study was approved by the inst itutional review committee and all individuals gave informed consent a nd were prospectively studied (median 13 months, range 1 to 47 from th e date of the scintigraphy to May 1995). RESULTS: Organ localization o f I-123-SAP, indicating the presence of substantial visceral amyloid d eposits, was observed in all patients in group 1 and 2. The organ upta ke of I-123-SAP included the spleen (1 patient was splenectomized) in 20 of 23 cases (87%), the liver in 15 of 24 (60%), and the kidneys in 6 of 24 (25%). Myocardial I-123-SAP was never seen although 13 out of the 24 patients had clinical or echographic data for amyloidosis. Twen ty-four hour tissue retention was significantly elevated in all patien ts (group 1 and group 2): 55.66% +/- 19.16% in group 1 and 34.37% +/- 24.92% in group 2, as compared with normal levels <24%. The sensitivit y of the technique was 79% when only organ uptake was considered but r eached 100% when tissue retention was also considered. The 24-hour tis sue retention might be correlated with the severity of the amyloidosis : mean survival in patients with tissue retention greater than 50% was 11.3 months versus 24.5 months in patients with levels less or equal to 50%. Five of the 6 patients with multiple myeloma without evidence of amyloidosis had abnormal I-123-SAP imaging and 24-hour tissue reten tion levels. In 2 of them, amyloidosis was secondly detected. In the 9 patients who had two scintigraphies, variations in 24-hour tissue ret ention values were in accordance with the clinical evaluation. CONCLUS IONS: Spleen and liver distribution of amyloidosis is mostly revealed by I-123-SAP scintigraphy in patients with AL amyloidosis. The uptake of I-123-SAP appeared in proportion to the quantity of amyloidosis pre sent in different tissues, and the relative quantity of amyloid deposi ts in the myocardium, carpal tunnel, digestive tract, and kidneys was often small and seldom visualized by I-123-SAP scintigraphy. In contra st 24-hour tissue retention levels were abnormal in all cases of known AL amyloidosis. This may be a positive argument for the diagnosis of amyloidosis when histopathological tests are normal. Tissue retention levels appear important as they may be correlated with survival.