A 70-year-old woman is referred by a GP colleague to the hospital with a breast lump.
She is asymptomatic but her investigations reveal:
Corrected calcium 2.72 mmol/L (2.2-2.6)
Phosphate 0.80 mmol/L (0.8-1.4)
Alkaline phosphatase 110 U/L (45-105)
PTH concentration 5.1 pmol/L (0.9-5.4)
Whilst your colleague is away, you are shown these results by one of the receptionists.
Which of the following is the most likely diagnosis?
(Please select 1 option)
Bony metastases
Chronic vitamin D excess
Ectopic PTH related peptide (PTHrp) secretion
Multiple myeloma
Primary hyperparathyroidism
Explanation:
This patient has hypercalcaemia with a borderline low phosphate concentration, but an inappropriately normal parathyroid hormone (PTH) concentration.
This suggests hyperparathyroidism which is a relatively common disorder amongst elderly females.
Vitamin D excess would be expected to cause an elevated phosphate.
Bony metastases and multiple myeloma can both result in hypercalcaemia, which should result in a suppressed PTH.
PTH related peptide is a common cause of hypercalcaemia in malignancy. It is not usually detected by normal lab tests for PTH and therefore you would expect a low PTH in the setting of hyperclcaemia.
If this was multiple myeloma you would expect a physiological decrease in PTH as a response to the hypercalaemia. PTH is inappropriately normal here, as mentioned above, which should lead you to a diagnosis of primary hyperparathyroidism.