SAT-341 Hyperparathyroid Crisis Precipitated by Rapid Correction of Symptomatic Hypercalcemia in an Occult Ectopic Parathyroid Adenoma

Background: Parathyroid adenomas (PA) are typically benign, slow-growing tumors causing gradual increase in parathyroid hormone (PTH) and serum calcium (s.Ca) levels. Hyperparathyroid crisis is a rare and potentially fatal syndrome, which occurs due to rapid elevation of PTH and s.Ca levels (s.Ca >15mg/dL). This can potentiate severe metabolic derangements, manifesting as altered mental status (AMS), renal insufficiency and cardiac arrhythmias. We present a case of hyperparathyroid crisis in the setting of an occult ectopic parathyroid adenoma. Case: 75 year old female with a medical history of osteoporosis, hypertension and Parkinson’s disease, presented to our hospital with AMS and one week history of diarrhea. She was recently hospitalized for pneumonia and treated with antibiotics. Biochemical analysis revealed corrected s.Ca 15.4mg/dL (8.2- 9.6mg/dL; 7 days prior s.Ca was 9.7mg/dL), renal insufficiency (Cr 2.26mg/dL; baseline 1.2) with normal serum phosphorus, magnesium, 25-hydroxyvitamin D and alkaline phosphatase. PTH was found to be elevated at 75pg/mL (15-65pg/mL). She was treated with aggressive intravenous hydration and calcitonin 200mg BID for 3 days. Her s.Ca appropriately trended down. However, her PTH level continued to rise: 319pg/mL 12 hours later, 591pg/mL on day 2 and peaked to 1,242pg/mL on day 3. CT angiography neck showed an incidental finding of a heterogeneous, possibly necrotic, soft tissue nodule in the left paraesophageal region. Additional work-up with technetium 99 Sestamibi scan revealed persistent activity in the upper tracheoesophageal groove consistent with an ectopic PA. She underwent parathyroid exploration with excision of an enlarged ectopic left superior parathyroid adenoma, confirmed on histopathological analysis. The remaining parathyroid glands were normal. PTH declined to 34pg/mL postoperatively. Her mental status improved significantly returning to baseline within a few days with normal PTH and s.Ca levels. Discussion: Secretion of PTH is mediated by s.Ca via the calcium sensing receptors (CaSR). Studies have shown that patients with PA have decreased expression of the CaSR leading to an autonomous rise in PTH secretion and a higher PTH-calcium set point. In our case, the patient initially presented with a mildly elevated PTH level and symptomatic hypercalcemia. The rapid correction of s.Ca levels precipitated a remarkable rise in PTH levels. We postulate that this was caused by a possible upregulation mechanism in calcium sensing by adenomatous parathyroid tissue that is responsive to acute lowering of s.Ca levels, triggering a hyperparathyroid crisis. Reference: (1) Corbetta S., et al. Calcium-sensing receptor expression and signaling in human parathyroid adenomas and primary hyperplasia. Clinical Endocrinology. 2000; 52(3):339-48.