Parathyroid Tumors in Dogs and Cats


Key Points

Parathyroid tumors usually are benign

Because these tumors produce excessive amounts of parathyroid hormone, the calcium level in the blood becomes abnormally elevated and has profound effects on other body systems

The most common early warning sign of a parathyroid tumor is increased thirst and increased urination

Surgery has been and still is an excellent form of treatment for these tumors. Other treatments are available and seem to work well

Prognosis is generally excellent following treatment

 

Introduction

Parathyroid tumors are uncommon in dogs and much less common in cats. These tumors usually are benign, meaning that they usually do not metastasize or invade into nearby tissues. They usually are very small tumors that raise a lot of havoc in the affected patient’s body, because they produce excessive amount of parathyroid hormone. Multiple parathyroid tumors are found in about 10% of affected patients. Breeds that most commonly develop this problem include Keeshonds, Labradors retrievers, and German shepherds.

 

Anatomy and Physiology

Both dogs and cats have four parathyroid glands, two on each side of the neck. The parathyroid glands are attached to the surface or are imbedded within the thyroid glands. One parathyroid gland is located on the top pole (end) of the thyroid and the other is located on the bottom pole. Normally these glands are about 2 to 3 mm in diameter and are tan colored. The glands produce parathyroid hormone which causes the calcium level in the blood to increase. Because many electrical systems of the body’s organs such as the kidneys, bowels, muscle, and brain are totally dependant on calcium, a change in the normal level of this important element in the blood can be very harmful to the pet. In addition, high calcium levels can cause stones to form in the urine.

 

Signs and Diagnosis

Signs of hyperparathyroidism develop as a result of abnormally high calcium levels in the blood. Most common signs of this condition include increased thirst and urination. Subsequently, lethargy, weakness, and poor appetite may be noted. Signs such as straining to urinate, passage of blood-tinged urine or the inability to pass urine may be caused by calcium-based stones. Cats can have diarrhea and vomiting as additional signs. Because the relatively small parathyroid tumors are located deeply within the neck in dogs, they usually cannot be palpated. In cats, however, these same tumors can be palpated along the side of the neck.

A complete blood count, chemistry profile and urine testing are completed in the initial stages of the evaluation. Blood tests showing an elevation of the calcium level may be due to a parathyroid tumor, however, there are many other diseases that may elevate the calcium in the blood. To confirm a diagnosis of a functioning parathyroid tumor, a parathyroid hormone level is measured from a blood sample. Ultrasound of the neck frequently can identify these small tumors within the neck. In addition, ultrasound is used to check the bladder and kidneys for stones. The blood work will also be evaluated to check for damage to internal organs that may have occurred from the high blood calcium levels.

 

The Day of Surgery

In preparation for surgery, your pet should be fasted starting at 10 PM the night before surgery, however water does not need to be with held. To help prevent heartburn after surgery, a single dose of Pepcid AC (10 mg tablet per 20 pounds of body weight) should be administered at 6 AM at home on the day of surgery. Our anesthesia and surgical team will prescribe a pain management program, both during and after surgery, that will keep your companion comfortable. This will include a combination of general anesthesia, injectable analgesics, and oral analgesics.

 

Treatment

Initial evaluation of the patient will determine if the kidneys, heart or nervous system are affected by the high calcium levels. If this is the case, treatment with medication and intravenous fluids may be needed prior to removal of the parathyroid tumor.

There are two treatment options available to ablate a parathyroid tumor. The least invasive technique is performed under ultrasound guidance and involves the destruction of the gland with an injection of alcohol or heat via a radiofrequency needle. The alcohol injection technique is successful with one injection in about 90% of the cases. The heat treatment is about 50% successful after one treatment. With these techniques, damage to surrounding vital structures such as the nerves that control the voice box have been reported to be temporary, however, permanent complications may be possible.

Surgery is another option in which an incision is made on the under side of the neck. The parathyroid tumor is removed with a relatively simple procedure. Although this does involve a more invasive approach, vital structures can be more carefully preserved versus with the minimally invasive techniques.

 

Aftercare and Results

After surgery, you can continue to give your pet a prescribed pain reliever to minimize discomfort. It’s also extremely important to limit your dog’s activity for 3 weeks after surgery.

About 50% of dogs that have a parathyroid tumor removed will develop a low calcium level in the blood. Dogs that have a high calcium level (>14 mg/dl) prior to surgery are much more prone to developing this problem. Left untreated, a low calcium level could be fatal in some patients. Warning signs of this problem may include rubbing the face, dilation of the pupils, twitching muscles, loss of appetite, weakness and seizures. If any of these signs are seen at home, please call us as soon as possible and bring your companion in for an evaluation. If blood tests show that the calcium level is low in your pet’s blood, medication will be prescribed for a few weeks until the remaining parathyroid glands start functioning again.

If your companion is recovering well following surgery and no complications develop, the healing process will be monitored by the surgeon with one follow-up exam scheduled two weeks after the surgery.

The overall prognosis for your pet should be favorable following treatment of a parathyroid tumor, as this disease can be cured, yet left untreated it can cause irreversible damage to internal organs.


 


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