Case of the week

A 57 year old woman was referred to me for asymptomatic hypercalcemia, Ca 10.8. This was discovered incidentally during her routine physical.

Her family history is noteworthy for hyperparathyroidism in her mother, who underwent 3 1/2 parathyroidectomy many years ago.

Laboratory testing reveals:

Ca 10.8, PTH 45 pg/mL (normal 15-65), Phosphorus 2.3 mg/dL (normal 2.5-4.5), Creatinine 0.54 mg/dL.

How would you proceed?

Answer:

The 'inappropriate normal' PTH in the context of hypercalcemia suggests this to be a parathyroid issue. Therefore the next step should be to obtain 24-hour urine calcium (and creatinine) to determine the extent of hypercalciuria, and to calculate the fractional excretion of Calcium to rule out familial hypocalciuric hypercalcemia.

In this case, the patient's fractional excretion of Calcium was only 0.3%. The parathyroid imaging was negative for parathyroid adenoma, suggesting this to be a case of FHH.

This autosomal dominant condition is usually benign and leads to no problems usually associated with primary hyperparathyroidism. However the patient, family and their physicians need to be made aware of this as FHH can sometimes be diagnosed as primary hyperparathyroidism, putting patients through an unnecessary noncurative surgery, which is what I suspect happened to her mother.

Mutations of the Calcium Sensing Receptor (CaSR) can also be performed, but probably would not add anything to the case. I've only tested this once in a patient who was convinced she needed surgery to have her parathyroids removed; the positive test allowed me to convince her she did not need surgery.

Thanks for the comments!