SUN-833 - Spontaneous Remission of Recurrent Primary Hyperparathyroidism

Background:
Definitive treatment of primary hyperparathyroidism is surgical. Cinacalcet is not curative and is indicated in those patients who are not surgical candidates and have severe hypercalcemia or are symptomatic. This medication lowers serum calcium and parathyroid hormone by activating the calcium-sensing receptor on parathyroid cells but does not lead to remission. Spontaneous remission of recurrent primary hyperparathyroidism is rare.

Case Presentation:
A 63-year-old man presented for evaluation of recurrent primary hyperparathyroidism. He was initially diagnosed 21 years earlier and underwent neck exploration with removal of a left inferior parathyroid adenoma, without biochemical cure. Further evaluation identified an ectopic fifth parathyroid gland in the left upper chest, resection of which resulted in biochemical remission. Hypercalcemia recurred 7 years ago (calcium up to 11.7 mg/dL, PTH 158.5 pg/mL). He underwent repeat neck exploration and left thyroid lobectomy without identification of abnormal parathyroid tissue and remained hypercalcemic. Subsequent ultrasound and sestamibi scan suggested a right-sided parathyroid adenoma; however, a third neck exploration failed to localize an adenoma. Due to persistent bone pain, arthralgias, and cognitive symptoms, cinacalcet was initiated (30 mg daily) with only transient biochemical improvement. Further surgical exploration later identified and removed a right inferior parathyroid adenoma, complicated by intraoperative vascular injury, and the patient was subsequently managed medically with cinacalcet, titrated up to 180 mg daily and later stabilized at 120 mg daily. Despite multiple localization studies, including sestamibi SPECT-CT most recently 2.5 years ago, no residual adenoma was identified. Over the past 6 months, cinacalcet was progressively reduced and discontinued due to recurrent symptomatic hypocalcemia (muscle cramps, esophageal spasms, palpitations). Serum calcium and PTH have remained within the normal range for several months after discontinuation, and the patient remains asymptomatic.

Discussion:
Spontaneous remission of primary hyperparathyroidism is rare, and spontaneous remission in the setting of recurrent disease has not been well described in the literature. One proposed mechanism is infarction or hemorrhage of a parathyroid adenoma, which has been reported in cases of spontaneous biochemical normalization. However, spontaneous remission does not necessarily indicate definitive resolution, as recurrence following transient remission has been described. In this context, sustained biochemical remission after discontinuation of cinacalcet raises important questions regarding the underlying disease pathology and the durability of remission. Ongoing surveillance with serial calcium and parathyroid hormone measurements remains essential.

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