Chin Med J (Taipei) 1998;61:S176.

Clinical Practice on Electrolyte Disorders: Calcium Disorders

Shang-Jyh Hwang, M.D.

Section of Nephrology, Department of Internal Medicine, Kaoshiung Medical School Hospital

Abstract

In general, the disorders of calcium metabolism involve the functions of four organs: parathyroid, kidney, intestine, and bone. The hormones related to regulation of calcium include parathyroid hormone (PTH), vitamin D, PTH-related protein (PTH-rp), and calcitonin.

Clinical situation:

I. Hypercalcemia: Hypercalcemia causes multiple organ dysfunction, such as conscious disturbance, arrythmia, urolithiasis, renal failure, etc. It may be caused by either PTH-related or PTH-unrelated etiologies.

(1) Primary hyperparathyroidism is usually explained by a monoclonal cell growth and PRAD1 overexpression (11q13) may play a part in the pathogenesis of a large proportion. It can also be a component of MEN disorder.

(2) Hormonal hypercalcemia of malignancies (HHM) is mediated by the action of PTH-rp (a quite ancient molecule than PTH) on bone to release calcium. On the other hand, metastatic malignancies to bones also cause hypercalcemia-not by PTH-rp.

(3) Tuberculosis-associated-hypercalcemia is mediated through the action of increased vitamin D production from the 1-a-hydroxylase of activated macrophages.

(4) Other granulornatous diseases and multiple myeloma.

(5) Defect of the newly identified calcium-sensing receptor explains the development of several calcium disturbance-familiar hypocalciuric hypercalcemia, severe neonatal hyperparathroidism.

II. Hypocalcemia: Hypocalcemia usually manifests with neuromuscular dysfunction, such as muscle cramping, seizure. It can also be PTH-related or PTH-unrelated.
(1) Hypoparathroidism, either idiopathic or iatrogenic.
(2) Pseudoparathyroidism. PTh receptor defect.
(3) Renal tubular disorder. Often associated with renal tubular acidosis.
(4) Severe renal failure-hyperphosphatemia and vitamin D deficiency.
(5) Hypomagnesemia, often resulted from disorder of loop of Henle, may result in calcium dysregulation.
(6) Overexpression of calcium-sensing receptor-Idiopathic hypercalciuric hypocalcernia.

III. Investigation: To investigate a hypercalcemia patient, the following workup should be done (at least):
(1) Detailed history and thorough physical examination
(2) Serum albumin, inorganic phosphate, ionized calcium.
(3) Urinary calcium excretion.
(4) Arterial blood gas analysis.
(5) Hormone study: PTH, PTH-rp, Vitamin D.
(6) Image study: skeletal radiographs (KUB, skull, spine), abdominal and parathyroid sonography.

[Chin Med J (Taipei) 1998;61:S176.]