Abstract
Purpose18F-Florbetapir has been reported to show cardiac uptake in patients with systemic light-chain amyloidosis (AL). This study systematically assessed uptake of 18F-florbetapir in patients with proven systemic amyloidosis at sites outside the heart.MethodsSeventeen patients with proven cardiac amyloidosis underwent 18F-florbetapir PET/CT imaging, 15 with AL and 2 with transthyretin amyloidosis (ATTR). Three patients had repeat scans. All patients had protocolized assessment at the UK National Amyloidosis Centre including imaging with 123I-serum amyloid P component (SAP). 18F-Florbetapir images were assessed for areas of increased tracer accumulation and time–uptake curves in terms of standardized uptake values (SUVmean) were produced.ResultsAll 17 patients showed 18F-florbetapir uptake at one or more extracardiac sites. Uptake was seen in the spleen in 6 patients (35%; 6 of 9, 67%, with splenic involvement on 123I-SAP scintigraphy), in the fat in 11 (65%), in the tongue in 8 (47%), in the parotids in 8 (47%), in the masticatory muscles in 7 (41%), in the lungs in 3 (18%), and in the kidney in 2 (12%) on the late half-body images. The 18F-florbetapir spleen retention index (SRI) was calculated. SRI >0.045 had 100% sensitivity/sensitivity (in relation to 123I-SAP splenic uptake, the current standard) in detecting splenic amyloid on dynamic imaging and a sensitivity of 66.7% and a specificity of 100% on the late half-body images. Intense lung uptake was seen in three patients, one of whom had lung interstitial infiltration suggestive of amyloid deposition on previous high-resolution CT. Repeat imaging showed a stable appearance in all three patients suggesting no early impact of treatment response.Conclusion18F-Florbetapir PET/CT is a promising tool for the detection of extracardiac sites of amyloid deposition. The combination of uptake in the heart and uptake in the spleen on 18F-florbetapir PET/CT, a hallmark of AL, suggests that this tracer holds promise as a screening tool for AL.
Highlights
IntroductionAmyloidoses are a group of diseases in which misfolded proteins are deposited in tissues/organs in a highly aggregated form as amyloid fibrils, leading to multisystem disease
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Amyloidoses are a group of diseases in which misfolded proteins are deposited in tissues/organs in a highly aggregated form as amyloid fibrils, leading to multisystem disease
The higher sensitivity and specificity of 18F-florbetapir on dynamic than on late imaging suggests that earlier imaging would be best for imaging 18F-florbetapir uptake in the spleen
Summary
Amyloidoses are a group of diseases in which misfolded proteins are deposited in tissues/organs in a highly aggregated form as amyloid fibrils, leading to multisystem disease. About 30 such proteins have been reported to cause human disease, with the two most common types of systemic amyloidosis being transthyretin amyloidosis (ATTR) and acquired monoclonal immunoglobulin light-chain amyloidosis (AL). Age-related ATTR (ATTRwt) occurs due to wild transthyretin protein deposition in the heart, and is an increasingly recognized entity in the elderly. Systemic AL occurs due to an underlying plasma cell dyscrasia secreting an unstable immunoglobulin free light chain.
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