Endocrine Abstracts

A 64-year-old woman who had been on Lithium 600 mg/day for 6 years for affective neurosis, presented in 2005 with acute confusion associated with a serum calcium concentration of 3.02 mmol/ which improved with rehydration. She was followed-up in outpatients and diagnosed with ‘Lithium-associated hypercalcaemia’ likely to be secondary to parathyroid hyperplasia. Results showed a corrected calcium of 2.74 mmol/l (2.1–2.55), phosphate 1.00 mmol/l (0.74–1.52), parathyroid hormone (PTH) 26.2 pmol/l, normal renal function, alkaline phosphatase and ESR and a low urinary calcium excretion of 2.4 mmol/24 h (2.5–7.5). Her bone mineral density was normal. She was followed-up in outpatients for 2 years but continued to complain of non-specific symptoms. Parathyroid imaging in 2007 was suggestive of a left inferior parathyroid adenoma and this was confirmed on histology following minimally invasive parathyroidectomy. On 6 months follow-up, her corrected calcium remained normal, her non-specific symptoms had resolved and she remained on Lithium treatment.

The association of hypercalcaemia with Lithium therapy was first described in 1973 and since then over 50 cases have been reported. Lithium induces a shift in the PTH set-point to the right through effects on calcium receptor (CaR) signal transduction and therefore would be expected to result in parathyroid hyperplasia. However, a high prevalence of parathyroid adenomata in these patients has been demonstrated in some series, varying from 15–93% in cross-sectional studies. The effects of Lithium-associated hyperparathyroidism on bone mineral density and the risk of nephrolithiasis remain unclear and management of these patients is controversial. Discontinuation of Lithium is recommended but this is not always possible. We report a case of Lithium-associated hyperparathyroidism in which parathyroid imaging and parathyroidectomy were delayed and suggest that all such patients fulfilling NIH or local criteria for parathyroidectomy should be offered parathyroid imaging and/or surgical neck exploration.