Diagnosing and treating primary hypoparathyroidism in dogs and cats - Veterinary Medicine
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Diagnosing and treating primary hypoparathyroidism in dogs and cats
The diagnosis is fairly straightforward, and, regardless of the cause, treatment is aimed at relieving the clinical signs related to hypocalcemia. With early detection and proper care, the prognosis for patients with hypoparathyroidism is good.


VETERINARY MEDICINE


Hypocalcemic animals may respond to administration of a calcium salt with only a slight increase in measurable calcium. Neuromuscular signs usually resolve when the total calcium concentration reaches 6 to 7 mg/dl or the ionized calcium concentration reaches 0.6 to 0.7 mmol/L. The immediate goal of treatment is to control the neurologic and neuromuscular signs, not to normalize the laboratory values.1,3 Neuromuscular signs may improve immediately, but complete resolution of nervousness and behavioral signs may take one to two hours while the extracellular calcium equilibrates with the cerebrospinal fluid.1,2,10,11 Attempting to normalize calcium concentrations too rapidly places the patient at risk for hypercalcemia, hyperphosphatemia, and subsequent soft tissue mineralization because of deposition of calcium phosphate complexes (particularly in the skin), and renal parenchymal mineralization or calculus formation.1,3,13 The mass law effect, however, acts to lower the serum phosphorus concentration to compensate as the serum calcium concentration rises, so mineralization is rarely a clinical concern.1

Transitional treatment

At a minimum, monitor the serum calcium concentration daily during treatment.2,3 The duration of daily evaluation depends on the long-term therapy selected and status of the animal. The short-term goal is to maintain a total serum calcium concentration between 8 to 9 mg/dl until long-term oral therapy can begin.1,3 The initial dose of calcium salt administered to control clinical signs can last anywhere from one to 12 hours.1,2,4 At this stage, animals with hypoparathyroidism generally require additional parenteral calcium salt administration. Administration of a vitamin D analogue and oral calcium supplementation should also be initiated.

Oral therapy requires a minimum of one to three days of therapy before becoming effective. During this transitional period, parenteral calcium salts are given as either repeated intravenous boluses, subcutaneously (calcium gluconate only), or as a constant-rate infusion (CRI).1-3 When an animal requires additional intravenous fluid therapy support, avoid alkalinizing fluids since they decrease the serum ionized calcium concentration, exacerbating hypocalcemia.1,2 The length of therapy required is case-dependent. Hypoparathyroidism secondary to unilateral thyroidectomy may not require lifelong therapy. Bilateral parathyroidectomy resulting from thyroidectomy requires lifelong treatment as described in the section on long-term management.

Repeated intravenous boluses of calcium salts are the least optimal method of hypocalcemic treatment because the boluses cause peak and trough levels of extracellular calcium.1-3 Subcutaneous calcium salt administration is easy, inexpensive, and generally effective.1,3 Dosing guidelines vary, but the same dose of 10% calcium gluconate solution that was used initially to control tetany can be diluted 1:1 to 1:5 with sterile 0.9% sodium chloride solution and administered subcutaneously every six to eight hours.1-3,10,13 Alternatively, diluted calcium gluconate can be administered subcutaneously at 60 to 90 mg/kg/day, divided into three or four doses.1,2 However, 10% calcium chloride should not be administered subcutaneously because of tissue irritation and saponification of fat.1,2,10 Potential side effects, such as irritation and calcinosis cutis, do exist even with the use of diluted 10% calcium gluconate.13,14 If the calcium concentration remains stable after 48 hours of subcutaneous therapy, the frequency of parenteral calcium salt administration can be reduced to every 12 hours and then slowly withdrawn as the oral treatments begin to take effect.1-3


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Source: VETERINARY MEDICINE,
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