SAT-816 - Hypercalcemia Due to Ectopic Parathyroid Adenoma: A Unique Presentation of Tatton-Brown-Rahman Syndrome

Tatton-Brown-Rahman syndrome (TBRS) is a rare overgrowth/intellectual disability syndrome caused by de novo heterozygous variants in the DNMT3A gene, first reported in 2014. We report a case of a 19-year-old male with TBRS who presented with primary hyperparathyroidism (PHPT) due to an ectopic parathyroid adenoma.

The patient presented with hypercalcemia, a peak calcium level of 11.9 mg/dL (normal reference range: 8.8-10.4 mg/dL) with normal serum albumin, an elevated parathyroid hormone (PTH) level of 145 pg/mL (normal reference range: 15-65 pg/mL), normal kidney function, and mildly low vitamin D 25-OH level of 25 ng/mL (normal reference range: 30-80 ng/mL). 24-hour urine calcium was elevated to 642 mg/24 hours (normal reference range: 100-300 mg/24 hours). Imaging studies included a neck ultrasound which showed a 2.1 cm thyroid nodule and an extrathyroidal posterior hypoechoic nodule of 0.61 cm in the lower third of the right thyroid gland. A nuclear medicine single photon emission computed tomography-computed tomography (SPECT-CT) scan indicated a nodule on the left side of the thymus. Further evaluation with a four-dimensional CT (4D CT) was performed, revealing a small nodule of soft tissue in the right tracheoesophageal groove, posterolateral to the medial extension of the right thyroid gland, measuring 4 mm, with a 1.3 cm hypoattenuating nodule in the right thyroid gland without extracapsular invasion.

Given the discordancy of laterality on imaging, he underwent flexible bronchoscopy, left robotic video-assisted thoracic surgery (VATS), mediastinal mass resection, and partial thymectomy. Intraoperatively, his PTH level dropped from 281 to 50 pg/mL. Pathology confirmed an ectopic parathyroid adenoma in benign thymic tissue. Two weeks after surgery, calcium and PTH remained normal at 9.8 mg/dL and 38.0 pg/mL, respectively. Further genetic testing was pursued due to his complex clinical presentation, revealing a pathogenic de novo variant in the DNMT3A gene (c.2053G>A p.Gly685Arg), consistent with TBRS.

There is one other reported case of a 17-year-old male with TBRS and primary hyperparathyroidism due to an ectopic parathyroid adenoma.1 This case highlights a probable association between TBRS and PHPT, which can help inform clinical care for patients with TBRS and hypercalcemia, in addition to guiding future development of clinical guidelines for TBRS.

1. Kalil GH, Christopher WO, Brister KA, Orr WS. Treatment of Primary Hyperparathyroidism in the Setting of Tatton-Brown-Rahman Syndrome. Am Surg. 2023;89(7):3203-3204. doi:10.1177/00031348231157840

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