Hypoparathyroidism in cats  See also Parathyroid gland

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Hypoparathyroidism is a metabolic disorder characterized by hypocalcemia and hyperphosphatemia and either transient or permanent PTH insufficiency. The spontaneous disorder is uncommon in dogs and rarely reported in cats. Iatrogenic injury or removal of the parathyroid glands during thyroidectomy for treatment of hyperthyroidism is the most common cause in cats. Postoperative hypoparathyroidism secondary to parathyroidectomy for parathyroid tumour may occur due to atrophy of the remaining glands in either dogs or cats.

Diagnosis

Diagnosis is based on history, clinical signs, laboratory evidence of hypocalcemia and hyperphosphatemia, and exclusion of other causes of hypocalcemia (eg, hypoproteinemia, malabsorption, pancreatitis, renal failure). If idiopathic hypoparathyroidism is suspected, it should be confirmed by histologic examination of the parathyroid glands and documentation of parathyroid atrophy or destruction. Because the parathyroid glands are not grossly evident in animals with hypoparathyroidism, a unilateral thyroidectomy should be performed to ensure that adequate parathyroid tissue is available for examination. Determination of serum PTH concentrations might be helpful in the diagnosis of idiopathic hypoparathyroidism and may thereby eliminate the need for cervical exploratory surgery and histologic verification.

Treatment

Treatment is directed at restoring the serum calcium concentration to the low end of the normal range. This should include use of calcium supplements and vitamin D for either iatrogenic or idiopathic forms of hypoparathyroidism. If hypocalcemic tetany or seizures are present, calcium should be administered IV immediately. For maintenance of normocalcemia, oral calcium should be administered together with a vitamin D preparation.

The major complication associated with treatment of hypoparathyroidism is hypercalcemia, which develops as a consequence of over-treatment with calcium and vitamin D. If this occurs, calcium and vitamin D therapy should be temporarily discontinued; saline and furosemide should be administered if hypercalcemia is severe. With idiopathic hypoparathyroidism, long term management with vitamin D (with or without calcium supplementation) is necessary. In contrast, with iatrogenic hypoparathyroidism, spontaneous recovery of parathyroid function or accommodation of calcium-regulating mechanisms to the absence of PTH may occur weeks to months after surgery.