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.


The definitive test for hypoparathyroidism is evaluating a serum PTH concentration and a concurrent ionized calcium concentration.1,4 With a normal functioning parathyroid gland, PTH should be increased in response to a low ionized calcium concentration.2 An animal with hypoparathyroidism will have an inappropriately low serum PTH concentration (undetectable to low-normal) with a low ionized calcium concentration.2,7 So it is essential to perform both tests on the same blood sample. Serum samples should not be kept at room temperature for longer than two hours before they are refrigerated or frozen.7,8 Contact the laboratory for guidelines on handling samples before collecting them because incorrectly handled samples may yield erroneously low results.8


Table 1: Treatment of Primary Hypoparathyroidism
Table 1 provides an overview of the treatment recommendations for patients with primary hypoparathyroidism.

Initial treatment

Typically, affected animals are hospitalized for treatment because they require intensive care and frequent re-evaluation. Animals with tetany or seizure activity may respond to empirical administration of diazepam.1,3 With prolonged tetany, animals may become hyperthermic. As muscle relaxation occurs with treatment, a gradual normalization of body temperature occurs and additional cooling measures are typically not necessary.1-3 Serial monitoring of body temperature is recommended.3

When hypocalcemia has been established to be the cause of tetany, administer a slow intravenous bolus of a calcium salt.1,2 Ten percent calcium gluconate provides 9.3 mg/ml elemental calcium and is the preferred calcium salt because it is not irritating if accidentally injected perivascularly.1-3 The dosage of 10% calcium gluconate is 0.5 to 1.5 ml/kg (5 to 15 mg/kg) over 10 to 30 minutes, to effect.1-3,10 An alternative calcium salt is 10% calcium chloride, which contains 27.2 mg/ml elemental calcium.1,2 However, because of its higher calcium concentration, calcium chloride is more likely to cause severe tissue trauma and calcinosis cutis if injected perivascularly.1-3,11 The calcium salt must not be diluted in fluids that contain lactate, acetate, bicarbonate, or phosphates because calcium precipitation will occur, but 0.9% sodium chloride solution is appropriate.1-3

Monitoring an electrocardiogram (ECG) for potential cardiac arrhythmias is important during initial treatment for hypocalcemia because, when present, the arrhythmia may temporarily worsen. Various arrhythmias may occur with low ionized calcium concentrations, including bradycardia, tachycardia, and heart block.12 Because of the prolonged action potential in cardiac cells, the S-T and Q-T segments are often prolonged, with deep and wide T waves.1,3,12 Bradycardia, sudden elevation of the S-T segment, shortening of the Q-T interval, or ventricular premature complexes during administration all indicate cardiotoxicity from the calcium infusion,1-3 and the intravenous infusion should be temporarily stopped. When the ECG normalizes, reinstitute the infusion at a slower rate if further administration is needed to control tetany. The dosage provided above is a guideline only; the patient's response (resolution of neuromuscular signs) should guide individual dosing.1,3


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