Hypercalcemia is a well-known but underrecognized adverse effect of lithium. Most patients with lithium-associated hypercalcemia (LAH) have either nonspecific symptoms (eg, persistent tiredness, constipation, polyuria, polydipsia) or no symptoms. Clinically, LAH differs from primary hyperparathyroidism, though the management protocol of these 2 conditions is almost the same. In this article, we discuss how lithium can affect calcium and parathyroid hormone (PTH) levels and how LAH and lithium-associated hyperparathyroidism (LAHP) differs from primary hyperparathyroidism. We also outline a suggested approach to monitoring and management.
An insidious problem
Due to the varying definitions and methods used to assess hypercalcemia, the reported prevalence of LAH varies from 4.3% to 80%.1 McKnight et al2 conducted a systematic review and meta-analysis of studies of the relationship between lithium and parathyroid function that included 14 case-control studies, 36 case reports, and 6 cross-sectional studies without a control group. They found that the levels of calcium and PTH were 10% higher in lithium-treated patients than in controls.2
Pathophysiology. Lithium is known to increase both calcium and PTH levels. PTH is responsible for calcium homeostasis. It is secreted in response to low calcium levels, which it increases by its action on bones, intestines, and kidneys. Vitamin D also plays a crucial role in calcium homeostasis. A deficiency of vitamin D triggers a compensatory increase in PTH to maintain calcium levels.3
Calcium and PTH levels increase soon after administration of lithium, but the rise is usually mild and insidious. In a small proportion of patients who receive long-term lithium treatment, calcium levels can exceed the normal range. Patients who develop LAH typically have serum calcium levels slightly above the normal range and PTH levels ranging from the higher side of the normal range to several times the upper limit of the normal range. Patients might also experience elevated PTH levels without any increase in calcium levels. Lithium can affect calcium and PTH levels in multiple ways. For instance, it increases the reabsorption of calcium in the kidney as well as the reset point of calcium-sensing receptors. Therefore, only higher levels of calcium can inhibit the release of PTH. Hence, in cases where the PTH level is within the normal range, it is generally higher than would be expected for a given serum calcium level. Lithium can also directly affect the parathyroid glands and can lead to either single-nodule or multimodule hyperplasia.4
Long-term lithium use can cause chronic kidney disease (CKD), which in turn leads to vitamin D deficiency and hyperparathyroidism. However, secondary hyperparathyroidism with CKD is usually seen in the more advanced stages of CKD, and is associated with low-to-normal calcium levels (as opposed to the high levels seen in LAH).3-5
Primary hyperparathyroidism is the most common cause of hypercalcemia. Its prevalence ranges from 1 to 7 cases per 1,000 adults. The incidence of LAH/LAHP is 4- to 6-fold higher compared to the general population.6 Similar to LAH/LAHP, primary hyperparathyroidism is more common in older adults (age >60) and females. Hence, some researchers have suggested that lithium probably unmasks hyperparathyroidism in patients who are susceptible to primary hyperparathyroidism.3
Look for these clinical manifestations
Symptoms of primary hyperparathyroidism are related to high calcium and PTH levels. They are commonly described as “painful bones, renal stones, abdominal groans (due to hypercalcemia-induced ileus), and psychic moans (lethargy, poor concentration, depression).” Common adverse outcomes associated with primary hyperparathyroidism are renal stones, high risk of fracture, constipation, peptic ulcer, and pancreatitis.3,7
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