Endocrine Abstracts

Introduction: ¹⁸F-fluorocholine is a PET tracer used in the diagnostic work-up of patients with prostate cancer but was incidentally found to detect other tumours such as meningiomas, pituitary and parathyroid adenomas. ¹⁸F-fluorocholine PET/MRI is currently under investigation as an imaging tool for detecting hyperfunctioning parathyroid glands in primary or secondary hyperparathyroidism, especially in patients qualifying and willing to undergo parathyroid surgery where standard diagnostic localization procedures such as neck ultrasound and scintigraphy failed to localize an adenoma.

Case report: A male patient was diagnosed with X-linked hypophosphataemic rickets at the age of 5 years with severe dwarfism and leg deformities. Treated with phosphate supplements and calcitriol (and several orthopaedic correction surgeries), he reached reasonable growth and height, with at least partial correction of mineralization deficit and without obvious kidney damage. As expected, tubular phosphate reabsorption (TmP/GFR) remained low (<0.4 mmol/l) and FGF23 remained high. At the age of 23 years, he developed hypercalcaemia which persisted after treatment (including calcitriol) was stopped, i.e. a laboratory constellation of primary hyperparathyroidism. However, both neck ultrasound and dual-isotope ^99mTc-tetrofosmin and ¹²³I sodium iodide SPECT failed to localize an adenoma. Since the patient and his physicians preferred surgery (rather than cinacalcet) when feasible with maintaining normal parathyroid function, the patient consented to off-label imaging with ¹⁸F-fluorocholine PET/MRI, revealing intense focal tracer accumulation at the right lower position. Minimally invasive videoassisted selective parathyroidectomy was performed, resulting in an intraoperative drop of PTH from 258 to 73 ng/ml and subsequent normalization of serum calcium. Calcium and PTH remain normal for more than a year of follow-up, up to this writing.

Conclusion: Our finding suggests that ¹⁸F-fluorocholine PET/MR can be a helpful and sensitive tool to localize the dominant source of PTH in difficult selected cases where minimally invasive selective parathyroidectomy is considered the treatment of choice.