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. 

+A minimally invasive technique has been developed at ASCM to remove parathyroid tumors which minimizes pain postoperatively

+Prognosis is generally excellent following treatment

 

Downloadable forms/information for clients for initial visit:

Client-patient form

History sheet initial consultation for parathyroidectomy

Client education handout for parathyroidectomy

Discharge instructions for parathyroidectomy postop care

Covid protocol


Downloadable forms for referring veterinarians:

rDVM referral form



anatomy

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. Most parathyroid tumor are closely associated with the thyroid glands in the neck; however, ectopic parathyroid tumors can be  embedded in the base of the tongue, anywhere along the length of the neck or within the chest cavity.  Breeds that most commonly develop this problem include Keeshonds, Labradors retrievers and German shepherds.

 

Anatomy and Physiology

Dogs and cats have four parathyroid glands; two glands are located on each side of the neck. The parathyroid glands are attached to the surface or imbedded within the thyroid glands. One parathyroid gland is commonly 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 the function of organs such as the kidneys, bowels, muscle and brain are totally dependent 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 kidney failure and 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 test results will be evaluated to check for damage to internal organs that may have occurred from the high blood calcium levels. 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 functional  parathyroid tumor, parathyroid hormone level is measured from a blood sample collected from the pet. Ultrasound of the neck can identify these small tumors within the neck. In addition, ultrasound is used to check the bladder and kidneys for stones. 

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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.

A technique developed at ASCM is minimally invasive parathyroidectomy (MIP).  Traditional surgery involves a 4 inch incision on the ventral (front) of the neck.  MIP involves mapping the exact location of the parathyroid tumor with ultrasound imaging while the patient is positioned on the operating table.  During MIP, a 1/2 to 1" incision is made directly over the tumor, muscles are separated, tumor is exteriorized out of the incision and then removed.  At the conclusion of surgery,  local anesthetic called Nocita is injected in the surgical site, which provides pain relief for up to 72 hours after the procedure. 

 

Aftercare and Results

After surgery, you can continue to give your pet a prescribed pain reliever to minimize discomfort (most dogs do not need any pain medication with the MIP technique and Nocita). It’s also extremely important to limit your dog’s activity for 3 weeks after surgery.

About one third 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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