Imaging in systemic amyloidosis

Abstract

Diagnosis of systemic amyloidosis remains challenging. Histology, the current gold standard for diagnosis of amyloidosis provides limited information on the extent of the disease and is not useful for monitoring. Non-invasive imaging modalities offer an easy way to evaluate whole-body amyloid burden, accurately identify organ involvement, quantify and monitor disease progression and response to treatment. A literature search was performed using PubMed on the subjects of ‘amyloid imaging’, ‘SAP scintigraphy’, ‘imaging in cardiac amyloidosis’, ‘cardiac MRI’, ‘PET and amyloidosis’ and ‘nuclear imaging in amyloidosis’. ¹²³I-SAP scintigraphy is the best and the only modality in routine clinical use for assessing the extent and distribution of visceral amyloid deposition in all types of amyloidosis. Echocardiography remains the most important tool for assessing cardiac amyloidosis but cardiac magnetic resonance imaging is becoming increasingly valuable. Bone-seeking tracers like ^99mTc-DPD and pyrophosphate are beginning to have a role in imaging transthyretin cardiac amyloidosis. Specificity of each of the imaging modalities limits the utility of any one imaging method for all types of amyloidosis for all organs. ^99mTc-DPD has a high sensitivity and specificity to cardiac transthyretin amyloid deposits and its role in early diagnosis of this condition is under investigation. Further studies are needed with ¹²³I-mIBG to assess its utility in patients with early cardiac autonomic neuropathy. Positron emission tomography with tracers used for Alzheimer's disease imaging is an area of increasing interest in systemic amyloid imaging.