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A 63-year-old male had a history of kidney stones and recurrent hydronephrosis for more than 30 years. He received parathyroidectomy 1.5 years ago because of elevated serum calcium level (3.47… Click to show full abstract
A 63-year-old male had a history of kidney stones and recurrent hydronephrosis for more than 30 years. He received parathyroidectomy 1.5 years ago because of elevated serum calcium level (3.47 mmol/L, normal range 2.03–2.54 mmol/L) and parathyroid hormone (PTH, 872.27 pg/mL, normal range 15–65 pg/m), and the parathyroid adenoma was suspected. The pathological diagnosis was atypical parathyroid adenoma. Serum calcium and PTH levels decreased for a short period after surgery, but gradually increased accompanied by progressively impaired kidney function (f), and reached more than 4 mmol/L for serum calcium and 3000 pg/mL for PTH recently. 68Ga-DOTA-TATE PET and parathyroid 99mTc-MIBI SPECT were performed to detect culprit lesions, but none positive lesions was found (not shown). He was then enrolled in a 68Ga-DOTA-FAPI-04 (FAPI) PET/MR clinical trial (NCT04554719) to evaluate whether there is an occult tumor. Diffuse bone uptake was visualized throughout the body (a, b & d), similar to whole body bone scan, with diffuse bone absorption and sclerosis on CT, presenting as “salt and pepper” skull (c), rugger-jersey spine (e), consistent with the characteristic osseous changes of hyperparathyroidism [1]. Right nephrarctia was also observed (a, arrow). Combined with the history, the patient was diagnosed as metabolic bone disease resulted from long-term hyperparathyroidism. However, parathyroid lesions were not seen in different imaging modalities. Up to 5% of hyperparathyroidism cases develop osteitis fibrosa cystica due to excessive production of PTH [2]. Besides, histogenesis-specific expression of fibroblast activation protein (FAP) was reported in many bone diseases [3]. These may be the reasons of 68Ga-FAPI uptake. However, the exact mechanism still needs further study. As for significant elevated PTH level, it may be related to postoperative elevated PTH level which occurred in nearly one-third of primary hyperparathyroidism patients with the highest level of about 500 pg/mL [4], and secondary hyperparathyroidism resulted from chronic kidney disease [5]. This case suggests that 68Ga-FAPI PET may be used to show the bone changes caused by the parathyroid diseases.