6.1.2. Future Promising Scintigraphic Tracers

Another scintigraphic tracer studied in pSS patients is 99mTc-EDDA/Tricine-HYNIC-Tyr(3)-Octreotide (99mTc-HYNIC-TOC). This tracer binds to somatostatin receptors on cell membranes. These receptors were shown to be overexpressed in various inflammatory and autoimmune diseases, and were found on, among others, activated lymphocytes, endothelial cells, and the monocyte lineage in synovium of rheumatoid arthritis (RA) patients [94–96]. Anzola et al. [97] showed increased 99mTc-HYNIC-TOC uptake within salivary glands of pSS patients compared to controls, as well as a considerably higher sensitivity of 99mTc-HYNIC-TOC scintigraphy compared to conventional scintigraphy. Furthermore, they demonstrated that 99mTc-HYNIC-TOC scintigraphy was able to identify joint involvement in a cohort of 62 pSS patients, of which many patients (87%) reported joint pain. Another tracer with potential applicability for pSS is 99mTc labeled with rituximab, which is an anti-CD20 tracer that images B-lymphocytes. In a small experimental setting, this tracer showed variable uptake in salivary glands and moderate uptake in lacrimal glands in two pSS patients [98].

Together, 99mTc-pertechnetate scintigraphy is in many institutes no longer used as an imaging technique in the diagnostic work-up and follow-up of pSS. Although promising new scintigraphic tracers have been developed, conventional nuclear medicine has disadvantages, such as the limited resolution of 8-10 mm and the inability to quantify the exact uptake. Positron emission tomography (PET), combined with low dose or contrast-enhanced CT, has multiple advantages over conventional scintigraphy, such as better spatial resolution, faster imaging tracts, and the possibility to quantify tracer uptake. It would be of value to couple the promising tracers that are mentioned above to a PET radionuclide in order to study the added value of these PET tracers in pSS patients.
