28.9. SAP scintigraphy and sFLCs

Chapter 28

I123-labelled serum amyloid P (SAP) scintigraphy was developed at the National Amyloidosis Centre in the UK for the diagnosis and quantitative monitoring of amyloid deposits [634]. I123-labelled SAP localises rapidly and specifically to amyloid deposits in proportion to the quantity of amyloid present. Whole body SAP scintigraphy (a SAP scan) allows the identification and quantification of amyloid deposits in affected organs, which varies greatly between patients. Furthermore, serial measurements demonstrate that amyloid deposits exist in a state of dynamic turnover, with variations in SAP uptake mirroring clinical status. This is seen in patients during treatment with chemotherapy and is compared with the concentrations of sFLCs in Figure 28.12.

Investigations by Lachmann et al. [133] in 137 patients with AL amyloidosis confirmed the important relationship between amyloid deposits, as seen on SAP scans, and sFLC concentrations. Patients were divided into three groups dependent upon whether the SAP scans of the amyloid deposits showed regression, no change, or progression following chemotherapy. A good correlation with changes in sFLC concentrations was observed during the same period, indicating that sFLC measurments provided a simple measure of changes in disease status in patients with AL amyloidosis (Figure 28.13).