Endocrine Abstracts

Background: Primary hyperparathyroidism (PHPTH) refers to overproduction of PTH (parathyroid hormone) which leads to hypercalcaemia and hypophosphataemia. Preoperative imaging aims identification of a solitary parathyroid adenoma (PTA) or multiple gland hyperplasia. However, it is not always possible to identify the lesions, and in some situations imaging findings could be misleading.

Case report: A 48-year old male, with personal history of differentiated thyroid cancer in 1998 (at age 27), underwent total thyroidectomy and multiple radioactive iodine (RAI) treatments (cumulative dose 610 mCi). During follow-up, there was no evidence of recurrent disease. He was lost for follow-up for several years.

In August 2018, he presented with signs and symptoms of hypercalcaemia, and was diagnosed with primary hyperparathyroidism (PHPTH). The neck ultrasound revealed a 3-cm hypoechoic heterogeneous mass in the left suprasternal region, suggestive of PTA. In April 2019, he underwent a resection of the mass with lateral neck lymph node dissection, the pathology report described the 3–cm mass as schwannoma, all other lesions resected as reactive lymphadenopathy. Postoperatively, he had persistent PHPTH. In May 2019, a 99mTc-Sestamibi scintigraphy with SPECT-CT identified two lesions with high uptake: one in the sternocleidomastoid muscle, with uptake on early imaging (10 minutes), with almost complete washout on late imaging (3 hours); and the other one in the right upper thyroid bed, with persistent uptake on late imaging. These lesions were excised, and the former one was reported as a reactive lymphadenopathy, while the latter one was confirmed as a PTA. Postoperatively, PTH levels immediately dropped from 267 pg/ml to 50.1 pg/ml. However, during follow-up, we identified persistently high PTH and Ca levels (92.9 pg/ml and 12.8 mg/dl in Jul 2019, 76.5 pg/ml and 11.7 mg/dl in Jan 2020). He repeated scintigraphy in Jan 2020, with no unusual uptake identified.

Discussion: Our case emphasises the importance of scintigraphy for differential diagnosis in PHPTH, even if the neck ultrasound identifies a suspicious lesion. Both schwannoma and lymphadenopathy could have a high uptake on scintigraphy, however the washout pattern is different compared to PTA. On the other hand, it reminds of higher incidence of PHPTH in patients treated with RAI, previously reported in literature. Also, hyperparathyroidism was reported as a possible aetiological factor of schwannoma. Hence, we could hypothesise that the lesions identified in our patient represent a linked sequence of events rather than a simple coincidence, with RAI for thyroid carcinoma causing hyperparathyroidism, and the latter contributing to development of schwannoma.