Extracardiac 18 F-florbetapir imaging in patients with systemic amyloidosis: more than hearts and minds

Purpose 18 F-Florbetapir has been reported to show cardiac uptake in patients with systemic light-chain amyloidosis (AL). This study systematically assessed uptake of 18 F-florbetapir in patients with proven systemic amyloidosis at sites outside the heart. Methods Seventeen patients with proven cardiac amyloidosis underwent 18 F-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 123 I-serum amyloid P component (SAP). 18 F-Florbetapir images were assessed for areas of increased tracer accumulation and time–uptake curves in terms of standardized uptake values (SUV mean ) were produced. Results All 17 patients showed 18 F-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 123 I-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 18 F-florbetapir spleen retention index (SRI) was calculated. SRI >0.045 had 100% sensitivity/sensitivity (in relation to 123 I-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. Conclusion 18 F-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 18 F-florbetapir PET/CT, a hallmark of AL, suggests that this tracer holds promise as a screening tool for AL.