This supplementary information is presented as submitted by the corresponding author. It has not been copy-edited by NTvG.

Lithium is very successfully being used as a medication for the treatment of bipolar disorder. Lithium-induced hyperparathyroidism (LIH) is an unknown complication that can arise due to the long-term use of lithium. Symptoms of LIH are often similar to the underlying psychiatric illness for which lithium was indicated. Thus, it is difficult to differentiate between both. This article describes three patients with LIH whom each presented very differently.

In the first case of a 51-year-old woman, we show that LIH and the subsequent hypercalcaemia are often diagnosed by coincidence and that the diagnosis could have been made earlier if only a calcium measurement would have been performed. In the second case of a 47-year-old woman, we show that it can be quite complicated to locate the underlying aberration of the parathyroid and that medication may be an eligible alternative to surgery. In the third case of a 56-year-old woman, we illustrate the need for cogency regarding appropriate surgical strategy since recurrences of LIH are quite common.

In 1973, the first case of lithium-induced-hyperparathyroidism (LIH) was reported. Unfortunately, this undesirable side effect of lithium is still a problem that is easily overlooked. We show that due to the broad spectrum of symptoms, which are often quite similar to the underlying psychiatric illness for which lithium therapy was indicated; it is difficult to identify these patients. Prevalence of LIH varies among studies from 10 to 30%. Altogether, it is our recommendation that these patients should be screened for elevations of their calcium level for early detection of LIH in order to prevent unnecessary delay in the diagnosis of LIH. Additional research will be required to address the question of which surgical approach is best in these patients.