PARATHYROID TUMOURS

The blood calcium levels in cats and dogs is controlled by the parathyroid glands. These glands are small, flat and have chemical sensors which help determine if there is a decrease in calcium levels which will cause parathyroid hormone (PTH) to be secreted. PTH will stimulate the bones, intestines and kidneys to increase calcium levels. Most mammals have four parathyroid glands, located in pairs on either side of the throat. It is uncommon for tumors to develop on the parathyroid glands, however when they do, problems associated with them can be extreme. Excessive PTH may be secreted which will have a toxic impact on the brain, intestines and the kidneys.

Parathyroid tumors can affect any dog or cat breed. The cause of this condition is unknown and seems to be a random occurrence. Some breeds of dogs have shown to be more at risk. Keeshonds have proven to have a genetic predisposition for these tumors and should not be bred if they have this condition.

It may be difficult for an owner to detect signs of a parathyroid tumor due to the small nature and location of the glands. External signs are rare. The clinical signs are what should prompt the owner to get their pet checked on by a veterinarian, namely hypercalcemia (high calcium levels). Hypercalcemia can pose threats to the functionality of organs, even more so to the kidneys. The condition will cause abnormal function in the kidneys, causing the pet to urinate often and drink extra water for compensation of fluid loss. As a result of excessive calcium being passed through the kidneys, the development of calcium-based urinary stones is possible in the ureters, urinary bladder or kidneys. Intestinal function may also be compromised as a result of increased calcium levels, this may cause vomiting, loss of appetite and constipation. The pet may seem weak as muscle function can become abnormal due to hypercalcemia. If hypercalcemia persists for an extended period of time, there can be permanent damage to the kidneys and other organs with the development of calcium-phosphate complexes in the tissues.

During the yearly health checks of cats and dogs, your veterinarian should do a blood test. During these tests is how parathyroid tumors are usually diagnosed. Initial signs of hyperparathyroidism can be mistaken for old age by the owner. However, when hypercalcemia is found during a blood evaluation, the cause should be determined through further testing.

If your veterinarian suspects that the pet is suffering from a parathyroid tumor, they will test the levels of PTH in the blood to get a definitive result. The test will measure both PTH and PTHrP (PTH related-peptide). Both of these hormones can cause the calcium levels in the bloodstream to be elevated. However, PTH is only secreted by parathyroid glands whereas cancers such as multiple myeloma and lymphoma can cause PTHrP to be released. A parathyroid tumor is only suspected when PTH is elevated and PTHrP is undetectable. However, if the concentration of PTH is normal, but in the presence of hypercalcemia, there is still an abnormal secretion of hormones by the parathyroid gland which could mean a tumor is present.

The last test for diagnosing a parathyroid tumor, is an ultrasound of the parathyroid glands. This test is sensitive and allows an experienced ultrasonographer to detect any abnormalities. Parathyroid tumors look like spherical enlargements on the parathyroid gland. They can be quite large in relation to a normal parathyroid gland.

The options for treating parathyroid tumors are as follows:

• surgical excision
• ethanol ablation guided by ultrasound

General anesthesia will be required for both procedures. Thus, the pet will need to be evaluated pre-anesthetic to ensure it is supported appropriately. There may be a higher risk of blood pressure issues and cardiac arrhythmias if there is an extreme elevation of calcium levels.

Surgical excision requires the veterinarian to make a midline incision on the neck, behind the throat. Both sides will be explored to check on all parathyroid glands. Normally the parathyroid tumor is excised from the thyroid gland in order for the thyroid gland and other parathyroid glands to be spared.

The ultrasound-guided ethanol ablation option is less invasive. The general anesthesia is used to ensure that the pet does not move during ablation. The preparation is similar to that in surgery where the hair is clipped and skin scrubbed. The parathyroid tumor is identified by ultrasound. The ethanol will enter the skin through a syringe attached to a needle. The ultrasound imaging will assist with guiding the needle to the parathyroid tumor where the ethanol will be injected into it. The tumor will be destroyed due to rapid necrosis which is caused because the ethanol is toxic to the tumor. It is important that ethanol does not escape the parathyroid tumor as it can cause damage to the surrounding fine nerves. Sometimes the parathyroid tumor is not destroyed completely and repeat administration may be required.

It is essential that the chances of postoperative hypocalcemia is minimized. This is done through monitoring of blood calcium levels by your veterinarian and supplements of vitamin D or calcium if necessary. Your pet will be weaned off of supplements as the functionality of the parathyroid glands becomes normal.

Both procedures require you to pay close attention to your pet after surgery. Hypercalcemia is resolved fast after the parathyroid tumor is removed. Hypercalcemia would have suppressed the normal parathyroid glands. It can take a few days or longer for the function of parathyroid glands to return to normal. Calcium levels can drop to below normal during this time. The decrease of calcium levels (hypocalcemia) can result in seizures or death.

There is a good chance of long-term survival post-parathyroidectomy. Excision is curative in most cases as the parathyroid tumor is benign. It is rare for multiple parathyroid tumors to develop, howevr it is possible and has been reported. In the case of multiple parathyroid tumors, they will usually be removed during the same surgery.