At the time of this presentation, her PTH was 3,300 pg/ml despite treatment with cinacalcet. Her ionized calcium was normal (1.2 mmol/L) but she complained of poor concentration, fatigue and depression. Serum phosphorous and creatinine were normal. She had a normal sestamibi scan but an US revealed hyperplastic parathyroid tissue in her neck.
During the parathyroidectomy, frozen section revealed hypercellular parathyroid tissue that was removed. However, pre-op, intra-op and post-op PTH levels were elevated at >1700 pg/ml. Because of the persistently elevated PTH, it was considered a failed operation and calcium supplementation was not started post-op. However, within 3 hours of the operation, she developed perioral numbness, tetany and muscle spasms in her legs. Her ionized calcium was low (0.9 mmol/L) and her symptoms resolved after treatment with iv calcium. Her PTH remained elevated at 3000 pg/ml.
What is the reason for her acute hypocalcemia in this setting? Answer in the comments please.