Hypercalcemia and hypocalcemia

Table 47-2 Causes of Hypocalcemia Low Parathyroid Hormone Levels (Hypoparathyroidism) Parathyroid agenesis Isolated DiGeorge syndrome Parathyroid destruction Surgical Radiation Infiltration by metastases or systemic diseases Autoimmune Reduced parathyroid function Hypomagnesemia Activating CaSR mutations High Parathyroid Hormone Levels (Secondary Hyperparathyroidism) Vitamin D deficiency or impaired 1,25(OH)2D production/action Nutritional vitamin D deficiency (poor intake or absorption) Renal insufficiency with impaired 1,25(OH)2D production Vitamin D resistance, inclu...

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Vitamin D deficiency, impaired 1,25(OH)2D production (primarily secondary to renal insufficiency), or, rarely, vitamin D resistance also cause hypocalcemia. However, the degree of hypocalcemia in these disorders is generally not as severe as that seen with hypoparathyroidism because the parathyroids are capable of mounting a compensatory increase in PTH secretion. Hypocalcemia may also occur in conditions associated with severe tissue injury such as burns, rhabdomyolysis, tumor lysis, or pancreatitis.

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A detailed history may provide important clues regarding the etiology of the hypercalcemia (Table 47-1). Chronic hypercalcemia is most commonly caused by primary hyperparathyroidism, as opposed to the second most common etiology of hypercalcemia, an underlying malignancy. The history should include medication use, previous neck surgery, and systemic symptoms suggestive of sarcoidosis or lymphoma. Once true hypercalcemia is established, the second most important laboratory test in the diagnostic evaluation is a PTH level using a two-site assay for the intact hormone.

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Harrison's Hypocalcemia Internal Medicine Chapter 47. Hypercalcemia and HYPERCALCEMIA AND HYPOCALCEMIA: INTRODUCTION The calcium ion plays a critical role in normal cellular function and signaling, regulating diverse physiologic processes such as neuromuscular signaling, cardiac contractility, hormone secretion, and blood coagulation. Thus, extracellular calcium concentrations are maintained within an exquisitely narrow range through a series of feedback mechanisms that involve parathyroid hormone (PTH) and the active vitamin D metabolite 1,25-dihydroxyvitmin D [1,25(OH)2D].

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Table 47-1 Causes of Hypercalcemia Excessive PTH production Primary hyperparathyroidism (adenoma, hyperplasia, rarely carcinoma) Tertiary hyperparathyroidism (long-term stimulation of PTH secretion in renal insufficiency) Ectopic PTH secretion (very rare) Inactivating mutations in the CaSR (FHH) Alterations in CaSR function (lithium therapy) Hypercalcemia of malignancy Overproduction of PTHrP (many solid tumors) Lytic skeletal metastases (breast, myeloma) Excessive 1,25(OH)2D production Granulomatous diseases (sarcoidosis, tuberculosis, silicosis) Lymphomas Vitamin D intoxic...

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