A 44 year-old lady with a previous left superior parathyroidectomy seven years prior presented with symptomatic hypercalcaemia. Her histopathology then was that of ruptured parathyroid tissue encased in a thick fibrotic capsule, with cystic degenerative changes and haemorrhage. Her calcium (Ca) and parathyroid hormone (PTH) levels were normal prior to being lost to follow-up a year post surgery.
She had symptoms of nausea and vomiting on admission, with corrected Ca 3.23 mmol/L (2.1-2.6) and PTH 53.5 pmol/L (1.6-7.2), necessitating treatment with aggressive intravenous hydration and bisphosphonate infusion. Her parathyroid sestamibi was unremarkable. Ultrasound revealed the presence of an unusual hypoechoic and irregularly shaped nodule (10x8x12mm) posterior to the upper pole of left lobe thyroid at the same site of previous surgery, raising concerns about possible malignancy.
Neck exploration revealed multiple small parathyroid deposits around the carotid sheath, thyrothymic tract, and adjacent to the trachea on the left. Histopathology revealed hypercellular parathyroid tissue extending into surrounding tissue and fat, with mild cytological and architectural atypia, without vascular space invasion or perineural spread - raising the possibility of either parathyromatosis or low grade parathyroid carcinoma. Immunohistochemical staining pattern for parafibromin and PGP9.5 made the presence of HRPT2/CDC73 mutation unlikely, hence it was considered to be low risk for metastasis. Her serum Ca normalised immediately post operation and was maintained at 6 months, while her PTH remained mildly elevated (12.1 pmol/L) at six months.
Parathyromatosis and low grade parathyroid carcinoma can be difficult to differentiate as they share many overlapping features both clinically and histopathologically. Previous history of a ruptured parathyroid gland, and its occurrence in multiple locations ipsilateral to the previous parathyroidectomy site as seen in our case raise the likelihood of parathyromatosis. Though rare, parathryomatosis should be considered in cases of recurrent hyperparathyroidism with the aforementioned features.