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Parathyroid/Bone Disorders

(11.11) Decoding the Puzzle: A Case of Familial Hypocalciuric Hypercalcemia and Primary Hyperparathyroidism

Friday, May 10, 2024
12:10 PM – 12:25 PM CDT
Location: ePoster Showcase, Empire Ballroom Foyer, Level 2
Introduction : Hypercalcemia can arise from many different etiologies, with the most common cause being an inappropriate secretion of parathyroid hormone (PTH). Primary hyperparathyroidism (PHPT) can be due to a parathyroid adenoma, parathyroid hyperplasia, or carcinoma. Additionally, mutations in the calcium-sensing receptor (CASR) gene can lead to familial hypocalciuric hypercalcemia (FHH) resulting in mild to moderate hypercalcemia. These two conditions rarely occur together with limited cases in the literature.

Case(s) Description : We present an 81 year old female with a 30 year history of hypercalcemia, who was diagnosed with FHH about 6 years ago when urinary studies showed a calcium/creatinine ratio of 0.005. Her mother had calcium issues her whole life, and her daughter was recently found to have hypercalcemia. The patient was subsequently found to have elevated parathyroid levels of 92 pg/mL with an elevated corrected calcium of 12.2 mg/dL, and normal 25-hydroxy vitamin D. Her clinical condition includes osteopenia, rheumatoid arthritis and chondrocalcinosis with extreme pains in her joints. She underwent a parathyroid nuclear medicine scan that was not able to localize to a single parathyroid. She subsequently underwent parathyroidectomy of 3.5 glands, with pathology revealing parathyroid hyperplasia. Post-operatively, her calcium levels remained mildly elevated at 10.6 mg/dL, with parathyroid levels in the low normal range.

Discussion :

The incidence of having both FHH and PHPT is unknown, but their occurrence together is likely related to mutations in the CASR gene. A cohort study of patients with known CASR gene mutations found that 2.9% of them had both FHH and PHPT. Novel mutations of the CASR gene have been found in larger families with incomplete penetrance of this dual diagnosis. A urinary calcium to creatinine clearance ratio less than 0.01 makes FHH likely, but is not diagnostic of FHH; genetic studies documenting a CASR mutation is necessary to confirm diagnosis. This patient has not yet decided to undergo genetic testing, but has been encouraged, given that her family is also presenting with hypercalcemia and may potentially benefit from parathyroid monitoring and surgery. It is important to remember that these two entities are not necessarily mutually exclusive, and the presence of one does not rule out the other.