What is primary hyperparathyroidism?
Primary hyperparathyroidism is an endocrine disease characterized by excess secretion of parathyroid hormone (PTH), a hormone secreted by the parathyroid glands and which regulates calcium levels in the blood.
This excess PTH leads to hypercalcemia (an increase in blood calcium levels), which is the cause of many symptoms.
What causes primary hyperparathyroidism?
The majority of cases of primary hyperparathyroidism in dogs are the result of benign hyperplasia of one or more parathyroid glands. The gland(s) enlarge, causing them to produce more parathyroid hormone.
More rarely, hyperparathyroidism can be caused by parathyroid carcinoma, a malignant tumor of the parathyroid glands.
The disease can occur in any breed of dog, but a juvenile hereditary form has been described in the German Shepherd, suggesting that there are at least a few genetic factors that lead to its development. If necessary, the disease is the cause of growth retardation.
A hereditary transmission of the disease is also suspected in the Siberian Husky, the Golden Retriever and the Spitz.
What are the symptoms of primary hyperparathyroidism in dogs?
The symptoms of primary hyperparathyroidism in dogs are the consequences of increased calcium levels in the blood.
The signs of the disease are often non-specific and tend to get worse over time. They can group:
- polyuro-polydipsia (the dog drinks and urinates more), secondary to hypercalcemic nephropathy. This is the most common clinical sign.
- digestive disorders such as anorexia, constipation or vomiting,
- neuromuscular disorders such as muscle weakness or drowsiness,
- bone disorders that result in intermittent lameness, bone pain or frequent fractures. They are linked to increased levels of circulating parathyroid hormone which leads to a constant release of calcium from the bones,
- signs of acute renal failure,
- etc.
Sometimes, however, dogs with primary hyperparathyroidism show no symptoms and the disease is incidentally detected in blood tests by the veterinarian as part of an entirely different problem.
In rare cases where a malignant tumor is the cause of the disease, a mass can sometimes be felt upon careful palpation of the animal's neck.
Except for juvenile forms of the disease, hyperparathyroidism usually occurs in older dogs. 96% of dogs affected by this condition are over 7 years old.
How is primary hyperparathyroidism in dogs diagnosed?
If your veterinarian suspects primary hyperthyroidism in your dog, he will confirm his diagnosis with blood tests which will include dosages of parathyroid hormone and calcium in your dog's blood. If your dog has abnormally high levels of parathyroid hormone and calcium in the blood, this will confirm the diagnosis of juvenile hyperparathyroidism.
Additional examinations may be useful, such as an ultrasound of the neck to detect a possible tumor of the parathyroid glands as well as urinary analyzes to assess the animal's kidney function.
What treatment is available for primary hyperparathyroidism in dogs?
Surgical removal of the affected gland or glands is the treatment of choice for primary hyperparathyroidism: this is called parathyroidectomy. The operation can be tricky for the surgeon, as the glands are very small and he must retain enough normal parathyroid tissue to avoid the risk of postoperative hypocalcemia, a very serious complication of the procedure which could affect the dog for life. . But, when the operation is successful, the prognosis is generally excellent for a dog that does not suffer from kidney failure.
Other curative treatments exist such as ethanol necrosis or electrocautery.
The first technique involves injecting pure ethanol into the parathyroid gland using a needle on an anesthetized animal to destroy the tissue.
As for the second, it consists of destroying the glandular tissue by inserting a needle connected to an electric scalpel. It is also practiced on an anesthetized animal. Several procedures may be necessary to achieve normal parathyroid hormone levels.
There are also non-curative medical treatments that aim to reduce circulating calcium levels. Partially effective, they are generally only used to reduce the dog's serum calcium before surgery to reduce the risk of postoperative complications.
In case of associated renal failure, medical treatment is also put in place.
What are the postoperative consequences?
The most common complication of surgical treatment for hyperparathyroidism is a temporary drop in blood calcium levels. It takes a few days to a few weeks for parathyroid hormone and calcium levels to return to normal and operated dogs are usually hospitalized for 4-7 days after the operation for monitoring.
In dogs whose calcium levels drop too low, calcium supplementation may be needed for a period of time to support the body's calcium levels.
In any case, regular monitoring of blood calcium levels after the operation is necessary.