Merck Manual

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Professional Version

Overview of the Parathyroid Glands and Disorders of Calcium Regulation in Dogs and Cats


Kathleen Ham

, DVM, MS, DACVS, University of Florida

Reviewed/Revised Jun 2023

Calcium plays an essential role in normal biochemical and physiologic mechanisms in the body and has a complex homeostatic system. The parathyroid glands are integral to this homeostasis, and disorders of the parathyroid glands result in abnormal calcium homeostasis. Testing for diseases affecting calcium homeostasis will usually focus on evaluating concentrations of total calcium, ionized calcium, parathyroid hormone (PTH), phosphorus, parathyroid hormone-related protein (PTHrP), and vitamin D metabolites.

Primary hyperparathyroidism (PHPT) occurs when one or more parathyroid glands secrete excessive PTH, causing hypercalcemia. Although historically PHPT was thought of as a rare disease, the current practice of routine biochemical analysis for geriatric or presurgical screening detects PHPT with some frequency.

The clinical sequelae of hypercalcemia include gastrointestinal, urinary tract, and neurologic manifestations; however, some patients remain subclinically affected. Treatment includes surgical removal of the hyperfunctional gland(s) or ablation of the gland with heat or ethanol.

Hypoparathyroidism is characterized by lack of PTH and may occur spontaneously, from trauma, or iatrogenically. Clinical signs vary but include tetany, muscle fasciculations and cramping, abnormal mentation, seizures, arrhythmias, and death. Treatment includes calcium and vitamin D supplementation.

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