A BONY PREDICAMENT

CATCHING THE CULPRIT IN THE CHEST

Abstract

INTRODUCTION/BACKGROUND
We report a case of mediastinal parathyroid adenoma as a rare cause of severe hypercalcemia and bone deformities.

CASE
A 19-year-old male presented with progressively worsening scoliosis and restrictive chest wall deformity over 4 years. He underwent chest wall reconstruction surgery with insertion of a titanium plate. Hypercalcemia was incidentally diagnosed perioperatively. He had polydipsia and weight loss but denied other symptoms. Past medical history and family history were unremarkable. He was small in stature with a body mass index (BMI) of 12.6 kg/m2, severely scoliotic spine and pectus excavatum and no palpable neck masses. Skeletal survey showed multiple malunited fractures and lytic bone lesions. Biochemical investigations revealed severe hypercalcemia with a peak level of 4.38 mmol/L and a markedly elevated intact PTH (iPTH) level of 695.3 pmol/L. Initial technetium-99m-sestamibi (MIBI) parathyroid scintigraphy showed no uptake over the neck and neck ultrasound revealed no masses. A subsequent whole-body MIBI with SPECT-CT showed avid uptake at the anterosuperior mediastinum, corresponding to a contrast-enhancing mass seen on CT-scan, measuring 17 x 30 x 18 mm. Genetic screening was negative for mutations in CASR, MEN1, MEN2 and MEN4 genes. Hypercalcemia was controlled with subcutaneous denosumab and oral cinacalcet before subsequent surgical resection. The mediastinal mass removed measured 55 mm in diameter and weighed 12.5 grams. Histopathological examination revealed tissue predominantly comprising chief cells, confirming an ectopic PTH adenoma. Postoperatively, his iPTH levels normalized and he required high doses of alfacalcidol.

CONCLUSION
Mediastinal adenomas are ectopic parathyroid adenomas that form because of aberrant embryological migration of inferior parathyroid glands. They may pose a diagnostic challenge leading to unnecessary surgical explorations. MIBI scans can improve diagnostic accuracy. Ectopic parathyroid adenomas make up 16-22% of parathyroid adenomas, of which 6-13% are mediastinal adenomas. Patients with primary hyperparathyroidism and initial negative neck imaging should prompt suspicion and work-up for mediastinal parathyroid adenoma.