Endocrine Abstracts

JOINT2025

Introduction: Hypercalcemia is a common disorder, with primary hyperparathyroidism (pHPT) and malignancy accounting for most of the cases. The parathyroid hormone level (PTH) is crucial in differentiating between the two conditions being raised in the former and suppressed in the latter. In a few instances, the picture can be clouded by additional factors that alter the hormonal level and can lead to misdiagnosis. Case 1:A 72-year-old male known dementia, diabetes and COPD presented with increasing confusion. Initial work up revealed corrected calcium 3.16nmol/l (2.20-2.60). PTH 3.2pmol/l (1.7-1.9). Vitamin D 21.3 nmol/l. The unsuppressed PTH raised the possibility of pHPT. It was, however, difficult to ascertain given that PTH is lower normal. Serum ACE and protein electrophoresis were unremarkable, eGFR> 90. The endocrinologist advised checking Magnesium which was low 0.4nmol/l (0.7-1.00). The patient received i.v fluids and Mg. A test following correction showed suppressed PTH of 1.5pmol/l with corrected calcium level 2.95nmol/l in keeping with hypercalcaemia of malignancy. A CT scan showed abdominal lymphadenopathy measuring 2cm. At the MDT, the impression was this is likely lymphoproliferative malignancy but given his co-morbidities, the plan was to manage palliatively. Case 2:A 56-year-old female patient with a recent history of subarachnoid haemorrhage due to ruptured aneurysm was undergoing rehabilitation under the care of the stroke team when she was noted to have raised corrected calcium 2.83nml/l(2.20-2.60). PTH 4.7pmol/l (1.7-1.9). Vitamin D 29.2nmol/l, eGFR>90. Similarly, it was not clear if this is pHPT given the unsuppressed PTH level. Magnesium level was subsequently checked and found to be low 0.35nmol/l (0.7-1.00). Correcting the magnesium revealed suppressed PTH 1.0pmol/l. A CT scan showed a mediastinal mass which is currently been evaluated by the chest physician for consideration of biopsy.

Discussion: Whilst hypercalcaemia with suppressed PTH typically raises concerns of malignancy, unsuppressed PTH in the context of hypercalcaemia usually indicates parathyroid pathology. This is commonly encountered in parathyroid adenomas/hyperplasia but also in familial hypercalciuric hypercalcaemia and parathyroid malignancy. Nevertheless, many other factors could be contributing to the raised PTH level including magnesium or vitamin D deficiencies or chronic kidney disease. This could lead to confusion when trying to reach a diagnosis and formulate plans for further investigations. Our two cases are unusual as both demonstrate hypercalcaemia of malignancy in the presence of unsuppressed PTH due to unchecked hypomagnesaemia. It is of paramount importance to rule out these confounding factors prior to making a firm diagnosis.