Hypercalcemia, arrhythmia, and mood stabilizers.

Recent findings in a bipolar patient receiving maintenance lithium therapy who developed hypercalcemia and severe bradyarrhythmia prompted the authors to conduct a retrospective study of bipolar patients with lithium-associated hypercalcemia. A printout of all cases of hypercalcemia that presented during a 1-year period was generated. After eliminating spurious hypercalcemias or those associated with intravenous fluids, the authors identified 18 non-lithium-treated patients with hypercalcemias related to malignancies and other medical conditions (group A) and 12 patients with lithium-associated hypercalcemia (group B). Patients in group B were not comparable to those in group A, as the latter were medically compromised and were receiving multiple pharmacotherapies. Thus, two control groups were generated: group C1, which included age- and sex-comparable lithium-treated bipolar normocalcemic patients, and group C2, which included bipolar normocalcemic patients treated with anticonvulsant mood stabilizers. The electrocardiographic (ECG) findings for patients in group B were compared with those of patients in groups C1 and C2. It was found that these groups did not differ in their overall frequency of ECG abnormalities; however, there were significant differences in the frequency of conduction defects. Patients with hypercalcemia resulting from medical diseases and bipolar patients with lithium-associated hypercalcemia had significantly higher frequencies of conduction defects. Patients in group A had significant mortality at 2-year follow-up (28%), in contrast to zero mortality in the other three groups. The clinical implications of these findings are discussed.