Hyperparathyroidism in dogs occurs when your dog's parathyroid gland produces too much parathyroid hormone. Your dog's parathyroid glands are separate from your dog's thyroid glands; they are located in your dog's throat, next to your dog's thyroid gland, or sometimes inside the thyroid gland. The hormone they produce helps to regulate levels of calcium and phosphorous in your dog's blood. There are three types of hyperparathryoidism found in dogs.
Primary Canine Hyperparathyroidism
The first type of hyperparathyroidism affecting dogs is called primary hyperparathyroidism. This occurs when one of the hyperparathryoid glands is affected by cancer, or otherwised damaged, and begins to produce too much parathyroid hormone. As a result, blood calcium levels become too high. This type of hyperparathryoidism occurs mostly in geriatric animals.
Symptoms of primary hyperparathyroidism include listlessness, loss of appetite, vomiting, lethargy, excessive thirst and excessive urination. Because the symptoms appear so gradually, the disease may be quite progressed before symptoms become noticeable. Treatment involves surgical removal of the damaged gland. Your dog's blood calcium levels may fall dangerously after surgery. He'll need to remain under observation at the clinic until your vet has determined whether to administer calcium supplements and how much supplementation your dog needs.
Secondary Nutritional Hyperparathryoidism
Secondary nutritional hyperparathyroidism is the result of nutritional deficiencies. This variation of the disease occurs most frequently in puppies who are fed an all meat diet. An all meat diet contains high levels of phosphorous and low levels of calcium, and puppies who are fed an all meat diet will therefore develop calcium deficiencies. Dogs are carnivores, but they also need to eat bones in order to supply their bodies with adequate amounts of calcium.
A nutritional calcium deficiency can lead your puppy's parathyroid gland into overproduction, and as a result, your puppy's body will remove calcium from his bones in order to make up for low blood calcium levels. Puppies suffering from nutritional hyperparathyroidism may seem unwilling to move about, may assume a splay legged posture, and may suffer permanent bone growth deformities of the spine and pelvis. Their thin bones will break easily and they may develop arthritis as a result of the pressure that bone deformities can place on joints.
Secondary Renal Hyperparathyroidism
Dogs suffering from renal (or kidney) failure may develop hyperparathyroidism. Kidney failure diminishes the kidneys' ability to remove phosphorous from the blood. It also means they produce less calcitrol, a hormone that works alongside parathryoid hormone to maintain blood calcium levels. This results in high levels of parathryoid hormone, and continued low levels of blood calcium.
High levels of parathyroid hormone in dogs suffering renal failure can cause more extensive kidney damage. Your dog may also suffer brain damage, thinning of the bones and bone deformity. Treatment involves reducing your dog's blood phosphorous levels. Your dog may require a dietary change and your vet may administer phosphorous binders to minimize the amount of phosphorous your dog's digestive tract absorbs. Calcitrol supplements can help raise your dog's blood calcium levels.