Detection of Multiorgan Light Chain (AL) Amyloidosis with Whole Body F18-florbetapir PET/CT

22 Objectives: Systemic immunoglobulin light chain amyloidosis (AL) is characterized by multiorgan deposition of fibrils from misfolded immunoglobulin light chains. Detection of organ involvement in patients with systemic AL amyloidosis is, currently, challenging. Only patients with organ specific symptoms, abnormal laboratory values (heart and kidney) or abnormal biopsy are identified. Conversely, targeted amyloid imaging with F-18 florbetapir PET/CT has the potential for preclinical detection of AL amyloidosis in the whole body and in multiple organs. The primary aim of this study is to determine the frequency of AL amyloidosis in the various organs of patients with systemic AL amyloidosis using F-18 florbetapir PET/CT. Methods: This is a prospective study of 32 patients with biopsy proven systemic AL amyloidosis. All patients underwent a cardiac and partial whole body F18-florbetapir PET/CT: skull base to below the kidney scan field, from 60-90 minutes after injection of 350±56 MBq of F-18 florbetapir (3 minutes/bed position). Brain and cardiac uptake were not assessed in this analysis. Volume of interest (VOI) measurements were obtained using Hermes software for the parotid gland, tongue, thyroid, three separate lung fields (upper, mid, lower), liver, pancreas, spleen, kidney, paraspinal or gluteal muscle, anterior or posterior abdominal wall fat, lower thoracic spine vertebral body and humeral head. Standardized uptake values (SUVmax) were calculated for each organ VOI, and SUVmax ≥ 2.5 was considered abnormal in all organs other than the liver. Results: The study cohort consisted of 32 patients, 53% men, mean age of 61±6.1 years, and mean body mass index 26.1 kg/m2. AL amyloidosis was diagnosed by biopsy of the myocardium (22%), bone marrow (22%), fat pad (16%), kidney (16%), or other organs (25%). The median kappa 16.3 mg/dL (IQR 9.7-26.7) and lambda 70.5 mg/dL (IQR 13.9-283.1), and K/L ratio 0.29 (0.05-1.15). Clinically, organ involvement included kidney (28%, biopsy or urine protein >0.5 g/day), tongue (6.3%), lung (12.5%), and gastrointestinal tract (22%, biopsy or symptoms) and liver (0%). On F-18 florbetapir PET/CT, organ involvement included the parotid (N=14, 44%), tongue (N=18, 56%), thyroid (N=11, 34%), lung (N=9, 28%), pancreas (N=15, 47%), kidney (N=4,13%), spleen (N=7, 22%), muscle (N=2, 6%), fat (N=2, 6%), vertebral body (N=19, 59%) and humeral head (N=5, 65%). F-18 florbetapir is excreted primarily via the liver, therefore liver uptake was present in all patients. SUVmax measurements in a heatmap format are provided in the table. Conclusion: Abnormal F18-florbetapir uptake is seen in different organs and to different degrees in patients with biopsy proven systemic amyloidosis. Compared to clinical presentation, some organs were involved frequently (tongue, parotid, spleen, lung) while others were more rarely involved (kidney) on F-18 florbetapir PET. In most instances, tracer uptake was not associated with clinical symptoms and thus unrecognized. Early recognition of systemic organ involvement may help tailor treatment, and non-invasive monitoring of organ level disease may help to guide therapy including use of novel therapies to resorb amyloid fibrils.