Development of 'primary' hyperparathyroidism during lithium therapy: longitudinal study.

The bone mineral content and the serum levels of immunoreactive parathyroid hormone (iPTH), and protein-corrected calcium and magnesium were measured in 13 manic depressive patients before and during treatment with lithium. Initially all four parameters were normal. During the treatment the bone mineral decreased and the serum levels of iPTH, calcium, and magnesium increased. Although altered metabolism of parathyroid hormone cannot be ruled out, these data, together with other observations, suggest that a mild 'primary' hyperparathyroidism sets in quite early after institution of lithium therapy.