Non-parathyroid Hypercalcaemia in a Patient on Lithium Therapy: A Case Report

Lithium is a commonly used drug in the treatment of several psychiatric disorders. However, due to its narrow therapeutic range, vigilant monitoring is essential to detect adverse effects. While hypercalcaemia is a documented complication of lithium therapy, it is typically associated with hyperparathyroidism. This case report presents a 67-year-old female on prolonged lithium therapy who developed refractory hypercalcaemia that was not attributable to hyperparathyroidism. Discontinuation of lithium resulted in normalisation of calcium levels, confirming lithium-induced hypercalcaemia in the context of normal parathyroid hormone (PTH) levels. The existing literature predominantly discusses hypercalcaemia as a consequence of hyperparathyroidism in lithium users. This case challenges that paradigm, suggesting an alternative, as yet undefined, mechanism for lithium-induced hypercalcaemia.