The parathyroid glands are tiny glands which sit within the thyroid glands in a dog’s neck. They are not normally palpable.
An under active gland or hypoparathyroidism is an uncommon disease resulting from the reduced production of parathyroid hormone (PTH). It has no breed predilection, but it is most commonly seen in middle aged female dogs.
PTH is made is made by the 4 parathyroid glands (2 on each side of the neck) and is in charge of regulating blood calcium and phosphorus levels. It does so by affecting the amount of calcium and phosphorus absorbed by the gut, lost by the kidneys, and released by bones into the bloodstream. If there is too little PTH there is a decrease in blood calcium and an increase in blood phosphorus levels.
We don't exactly know why the parathyroid glands stop producing PTH, but it is suspected that it is immune mediated, so the animals own immune system attacks the hormone producing cells. More unusual causes would be trauma to the ventral neck damaging the glands or removal of the glands due to thyroid cancer.
The signs of hypoparathyroidism are a result of the low blood calcium which causes muscle tremors or twitching, stilted uncoordinated gait, restlessness, seizures, weakness, lethargy, loss of appetite and panting. Diagnosis is made by blood analysis initially picking up a low blood calcium level with increased phosphorus, and then definitively by measuring PTH levels.
Treatment involves supplementation of vitamin D and calcium. Vitamin D is required for absorption of calcium from the gut. If symptoms are severe e.g. seizures, then treatment intravenously is required. Once stabilised or if the dog is only showing minor signs, then oral administration at home by the owner is adequate. Dosages may need to be adjusted according to the dog’s symptoms and levels are monitored with blood tests. Treatment is lifelong but with the correct medication prognosis is excellent.
Hyperparathyroidism occurs when the parathyroid gland produces too much PTH resulting in high blood calcium. Primary hyperparathyroidism is rare and is due to a benign enlargement of the gland. It is seen in all breeds but has a higher prevalence in Keeshonds. Very rarely, primary hyperparathyroidism is due to a malignant tumour called a parathyroid carcinoma.
The most common clinical sign is an increased thirst, but a reduced appetite, lethargy and vomiting are also seen. Diagnosis is made following a routine blood screen showing a high blood calcium. Definitive diagnosis is made by measuring blood PTH levels. In a normal dog with high blood calcium the PTH level should be low. It is important to demonstrate a high PTH and high calcium level on the same sample.
Ultrasound scanning of the neck can identify which of the 4 parathyroid glands are affected and then surgical removal of this gland is performed to treat the condition. The calcium level post operatively should be monitored closely in case it drops too low until the remaining parathyroid glands kick in to maintain it.
Hyperparathyroidism is usually confined to one gland, but it can develop in subsequent glands, and these can be removed accordingly. Untreated dogs suffer a build-up of calcium deposits in body organs with the kidneys being especially susceptible.
Both hypo and hyperparathyroidism are rare diseases of the dog and there are many other common causes of the clinical symptoms that are displayed.1