Case description: We report a case of 37 year-old Thai woman with a peak serum calcium of 3.6 mmol/L in her third pregnancy. She had previously had hypercalcaemia in two previous pregnancies over a 6-year period but no past history of nephrolithiasis, fractures or renal impairment and no previous investigations. Previous pregnancies were uncomplicated. In this pregnancy, she was first found to have parathyroid (PTH)-mediated hypercalcaemia at 8 weeks gestation with serum calcium of 2.94 mmol/L and serum PTH 73.3 pmol/L, vitamin D 30 nmol/L. She was first referred for management of hypercalcemia at 32 weeks gestation. A 24-hour urinary calcium excretion and fractional excretion calcium were both elevated excluding familial hypocalciuric hypercalcaemia. Hypercalcemia was refractory to saline diuresis with frusemide, and calcitonin. Induction of labour occurred at 37 weeks Her baby had transient hypercalcaemia which normalised after 36 hours. Maternal hypercalcaemia persisted despite the use of pamidronate 1mg/kg. Further investigations including a Tc99m Sestimibi scan, showed low level increased tracer uptake at the lower pole of the right thyroid lobe with FNA confirming a parathyroid lesion. Bone densitometry showed osteopenia in the lumbar spine and femoral neck and osteoporosis in the left wrist. A right inferior parathyroidectomy was performed 13 months postpartum. Histopathology showed a 16x14x10mm encapsulated nodule with invasion to thyroid gland and areas of fibrosis. Immunohistochemistry was negative for parafibromin and positive for PGP 9.5, diagnostic for parathyroid carcinoma, low grade. Serum calcium normalised postoperatively while on maintenance dose of cholecalciferol and calcium carbonate.
Conclusion: Parathyroid carcinoma is a rare cause of hypercalcaemia. The diagnosis can be difficult due to overlapping features with benign adenoma but the use of immunohistochemical markers are diagnostic. The insidious presentation over seven years in a young female is unusual.