Co-existence of elevated PTH and PTHrP
Santhosh Lakshmi & Duncan Browne
Patients with significant hypercalcaemia unrelated to primary hyperparathyroidism have suppressed or undetectable levels of Parathyroid Hormone (PTH). We present a case where the hypercalcaemia was not due to primary hyperparathyroidism yet the PTH was elevated.
82 year old male was admitted with 2 weeks history of lethargy, vomiting, increased frequency of micturiton, light headedness and confusional state. Past medical history included Type 2 diabetes, hypertension and spontaneous vitreous haemorrhage. He was on Metformin 500 mg thrice daily, Lisinopril 20 mg twice daily, Amlodipine 10 mg once daily and Aspirin 75 mg once daily. General and systemic examinations were fairly unremarkable except epigastric tenderness. His initial blood investigations included sodium 139 mmol/L, potassium 4.3 mmol/L, bicarbonate 32 mmol/L, urea 10.8 mmol/L, creatinine 89 micromol/L, corrected calcium 3.61 mmol/L, phosphate 0.69 mmol/L and alkaline phosphatase 218 IU/L. His full blood count, liver enzymes were normal; ESR 15 mm/hr and myeloma screen negative. He was treated with intravenous fluids, frusemide and pamidronate. His chest and abdominal x-rays were normal. However incidental findings on a prearranged ultrasound scan showed multiple hyper echoic nodules with the largest measuring 8.3×6.2 cms. The parathormone (PTH) in the admitting sample was inappropriately elevated 60 nanogram/L (1565) suggesting a diagnosis of primary hyperparathyroidism. Subsequent alfa-foeta protein levels were grossly elevated 9222 IU/L and computed tomography of his liver confirmed a large primary hepatoma. Bone scan did not show any evidence of metastases. Parathyroid hormone related peptide (PTHrP) was then measured and found to be significantly raised 5.2 pmol/L (<1.8) in conjunction with the raised PTH. His serum calcium remained elevated at 3.33 mmol/L.
The biochemical picture was consistent with hypercalcaemia secondary to paraneoplastic syndrome (PTHrP) due to primary hepatocellular carcinoma co-existing with background primary hyperparathyroidism.
Alternative causes of hypercalcaemia should be considered despite elevated levels of PTH if the clinical picture dictates.