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Hyperparathyroidism in Dogs

Excessive Levels of Parathyroid Hormone in the Blood in Dogs

The parathyroid hormone plays a vital role in regulating calcium and phosphorus levels in a dog’s blood. It works by increasing blood calcium levels through the reabsorption of calcium from the bones. Situated adjacent to or alongside the thyroid glands, the parathyroid glands are small glands responsible for hormone secretion. The prefix “para-” indicates adjacency, while “thyroid” pertains to the nearby thyroid gland. These glands are situated side by side in the neck, near the windpipe or trachea. Hyperparathyroidism is a medical condition affecting the parathyroid glands, where overly active glands produce abnormally high levels of parathyroid hormone (also called parathormone or PTH) in the bloodstream.

Primary hyperparathyroidism occurs when a tumor forms in the parathyroid gland, leading to excessive parathyroid hormone production and subsequently elevated blood calcium levels (known as hypercalcemia).

Secondary hyperparathyroidism may result from a deficiency in calcium and vitamin D, often associated with malnutrition or chronic kidney disease over the long term.

While no genetic cause has been identified for primary hyperparathyroidism in dogs, its occurrence in specific breeds suggests a possible hereditary component in certain cases. Secondary hyperparathyroidism can develop alongside hereditary kidney disease, known as hereditary nephropathy, although it is not directly inherited. Keeshonds appear to be particularly susceptible to this condition. In dogs, the average age of onset is ten years, ranging from 5 to 15 years old.

Symptoms and Types

Primary hyperparathyroidism often presents without noticeable signs of illness in most dogs. The symptoms typically manifest mildly and are primarily attributed to the effects of elevated calcium levels in the bloodstream. These symptoms may include:

  • Increased frequency of urination
  • Heightened thirst
  • Loss of appetite
  • Lethargy
  • Episodes of vomiting
  • Weakness
  • Formation of urinary tract stones
  • States of stupor and coma
  • Palpable enlargement of the parathyroid glands in the neck

Nutritional secondary hyperparathyroidism arises from diets deficient in calcium and vitamin D or excessive in phosphorus, constituting a form of malnutrition. This condition may sometimes be accompanied by bone fractures and overall poor body condition.

Causes

Primary hyperparathyroidism typically arises from a tumor secreting parathyroid hormone (PTH) in one of the parathyroid glands. In most instances, only one gland is affected, and malignant tumors in these glands are rare.

Secondary hyperparathyroidism is primarily associated with malnutrition, stemming from either a deficiency of calcium and vitamin D or an excess of phosphorus in the diet.

Additionally, secondary hyperparathyroidism can be linked to chronic kidney disease over the long term. This condition occurs due to the kidneys’ inability to retain calcium, leading to its loss through urine. Moreover, reduced absorption of calcium in the intestines results from a deficiency in calcitriol, a hormone responsible for regulating calcium levels and absorption in the intestines, which is normally produced by the kidneys. Retention of phosphorus in the body may also contribute to this form of hyperparathyroidism.

The specific cause of primary hyperparathyroidism remains unknown, while secondary hyperparathyroidism is closely associated with calcium and vitamin D malnutrition or chronic kidney disease.

Diagnosis

Your veterinarian’s primary focus will be on ruling out cancer as the underlying cause of the disease. However, several other potential causes will also be taken into consideration, including renal failure and vitamin D poisoning, which may be present in certain rodenticides. Excessive calcium levels in the blood are also among the possibilities.

A urinalysis will help determine calcium and phosphate levels. Serum ionized calcium levels are typically within normal range in patients with chronic renal failure but elevated in those with primary hyperparathyroidism or hypercalcemia associated with malignancies. If kidney stones are suspected, your veterinarian may employ X-ray and ultrasound imaging to examine the parathyroid gland for the presence of tumors. If no abnormalities are detected through these diagnostic methods, surgical exploration of the thyroid and parathyroid region may be necessary.

Treatment

Primary hyperparathyroidism typically necessitates hospitalization and surgical intervention. In contrast, secondary hyperparathyroidism resulting from malnutrition or chronic kidney disease in stable patients can often be managed as outpatients. Your veterinarian might suggest calcium supplements to help stabilize blood and intestinal calcium levels. For cases related to long-term kidney disease, low phosphorus diets may also be recommended.

Surgery remains the preferred treatment for primary hyperparathyroidism and plays a crucial role in confirming the diagnosis. If a tumor is identified, surgical removal is often the most effective course of action. Medications will be prescribed based on the final diagnosis and treatment plan.

Living and Management

Following surgical removal of one or more parathyroid glands to treat primary hyperparathyroidism, it’s common for dogs to experience low blood calcium levels (hypocalcemia), particularly if their calcium levels were high before surgery, exceeding 14 mg/d. Your veterinarian will monitor serum calcium levels closely, typically checking them once or twice daily for at least one week post-surgery. Regular blood tests will also be scheduled to assess kidney function.

Prevention

There are no known preventive strategies for primary hyperparathyroidism. However, secondary hyperparathyroidism resulting from malnutrition can be prevented through proper nutrition.

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