The parathyroids are glands secrete parathyroid hormone (PTH, also known as parathormone), which helps regulate the amount of calcium in the bloodstream. When the levels of parathyroid hormone get too high, they cause hypercalcemia (excessive levels of calcium in the blood), which can cause a variety of problems.
Primary hyperthyroidism is when there is a parathyroid gland tumor that is releasing excessive levels of PTH, resulting in hypercalcemia. The tumors are usually benign, and surgical removal of the tumor can result in complete and permanent resolution of the problem.
Secondary hyperparathyroidism is caused by a deficiency of calcium and Vitamin D
- Chronic (long-term) kidney disease is a common cause, and treatment is palliative/supportive.
- Chronic malnutrition is less common when an appropriate pet food is supplied, but in cases of deficiency, dietary modification is the treatment.
Certain cancers can also secrete a parathyroid-hormone like substance that can cause hypercalcemia and the other effects of hyperparathyroidism. Other cancers can cause hypercalcemia in other fashions.
The parathyroid glands are associated with the thyroid glands on either side of the tracheal (windpipe), just below the larynx (voicebox). There is one thyroid gland on each side, and each thyroid gland has two parathyroid glands, one internal (within the gland) and one external (on the outside of the gland)
Hypercalcemia can be diagnosed on routine bloodwork. A special test for ionized calcium (the calcium not bound to proteins) is a more definitive test for hypercalcemia. If the kidney values are markedly elevated, secondary hyperparathyroidism may be suspected. Diet should be reviewed to rule out nutritional causes. In severe/chronic cases, radiographs (x-rays) may show demineralization of the bones and/or mineralization of soft tissues. A thorough physical exam can evaluate for the presence of associated tumors, such as a nodule in the location of the parathyroid gland(s) or anal sac(s). Chest and abdominal radiographs, as well as abdominal ultrasound, can identify or rule out the presence of certain types of cancer. Additionally, abdominal radiographs can also check for the presence of calculi (stones) in the bladder, kidney, etc.; hypercalcemia can increase the risk of certain types of stones.
Special blood tests confirm or rule out primary hyperparathyroidism, including the ionized calcium, the parathyroid hormone level, and a test for the parathyroid hormone-like substance. Ultrasound of the thyroid and parathyroid glands can help identify tumors unable to be felt externally and/or to confirm the origin of tumors felt externally. Advanced imaging, such as CT (Computed Tomography/CATscan), can help identify or rule out ectopic parathyroid tissue (meaning parathyroid tissue present beyond the parathyroid glands, such as in the chest).
Once a diagnosis of primary hyperparathyroidism has been made, surgery is the treatment of choice; in most cases, the tumor is benign, and the patient can be cured.
Medical therapy is designed to try to minimize the hypercalcemia and is generally reserved only for short-term use or when surgery is not an option. Intravenous fluids may help lower the calcium levels somewhat by flushing more fluid through the kidneys. Steroids, such as prednisone or prednisolone, can be very helpful in lowering the calcium levels, but can also have severe side effects, especially with prolonged use, such as causing diabetes, increasing the risk of infection, increasing the risk of stomach or corneal ulcers, and suppressing the adrenal glands. Similarly, diuretics, such as Lasix/Salix (furosemide), can sometimes further lower the calcium levels, but can also cause dehydration, electrolyte imbalance, or even kidney damage.
Additionally, the longer a patient is medically treated, the more severely the normal parathyroid gland(s) are suppressed, making it much harder for a patient to recover following surgery.
Further, keep in mind that hypercalcemia can cause weakness and lethargy. While owners may feel their pet is too old or too sick for surgery, owners are often pleasantly surprised by how much stronger, playful, and active their pet becomes once the calcium has been re-regulated.
There is an alternative to surgery in which ethanol (ethyl alcohol) is injected into the affected gland(s) via ultrasound guidance. The ethanol can necrose (kill) the gland and resolve the disease. However, if any ethanol leaks outside of the targeted gland, it could damage the thyroid gland or some of the important nerves passing through this area. Additionally, it is possible that the treatment may only destroy part of the targeted gland, allowing it to regrow and cause hypercalcemia again.
Given that this procedure also requires general anesthesia, carries a risk of major nerve damage, and may not be successful, I do not recommend it. In experienced hands, surgery is definitive and relatively safe and brief.
Such surgery should only be performed by a properly-trained specialist, such as a board-certified surgeon, as numerous vital structures are present in the neck and could be damaged by inexperienced hands.
Via an incision on the neck, both thyroid glands and each of their associated parathyroid glands are examined. Ideally, the tumor has already been identified via ultrasound and/or external physical examination; regardless, a thorough internal examination is required to be confirm the location and number of parathyroid glands affected. The affected gland(s) is/are removed along with a small amount of surrounding thyroid tissue to ensure complete removal, as any residual tumor tissue could regrow and cause a recurrence of problems. Any tissue removed is submitted to a pathologist for review to confirm the tissue type and to determine whether the tissue is benign or cancerous.
In uncommon cases, where multiple (or all) parathyroid glands are enlarged, the surgeon will likely remove 2 of the 4 glands in hopes of reducing the hypercalcemia
When a parathyroid tumor is present, it will continue to secrete parathyroid hormone even in the face of severe hypercalcemia. However, the normal gland(s) respond to hypercalcemia by decreasing their own production of parathyroid hormone. Glands that are not actively producing parathyroid hormone will atrophy (shrink in size and diminish in function). Typically, the gland with the tumor is significantly enlarged, while the normal glands are atrophied. Once the tumor is removed, the patient is only left with the atrophied glands; as a result, the calcium will drop rapidly. While hypercalcemia can cause serious problems, hypocalcemia (low blood calcium levels) can cause more immediately life-threatening problems. If the facility and staff are not appropriately prepared, a patient could die in the first 6-24 hours post-operatively, despite a successful surgery.
The staff caring for such a post-operative patient must be able to take blood levels every few hours and get immediate results to monitor the calcium level; they must also be able to safely supplement the pet's calcium intravenously. In the early post-operative period, a pet also will receive Vitamin D supplementation to help that pet maintain the appropriate calcium levels in its bloodstream. Specific types of Vitamin D should be formulated/compounded to the exact needs of a pet, which is based on his or her size; this should be compounded in advance of surgery, as it will be needed as soon as possible post-operatively. The patient needs to be monitored in the hospital 24 hours a day initially.
The length of time the pet was treated medically and how severely the calcium had been elevated determine how severely the remaining parathyroid gland(s) had been suppressed, which in turn determines how long it will take them to regenerate/recover. Once a pet is eating, oral calcium supplementation (such as Tums or a generic equivalent) can be instituted. Once calcium levels are holding steady, the IV supplementation is tapered off slowly. If the calcium levels are maintained on oral calcium and Vitamin D supplementation, the pet can be sent home, with a plan to recheck calcium in the next 24-48 hours. As the calcium levels are maintained and as the normal parathyroid glands regenerate, the pet can be tapered slowly (while continuing to monitor levels) off of the oral supplementation over a period of a few weeks.
Most pets stay in the hospital for 24-48 hours post-operatively, and the supplementation/tapering takes place over a few weeks.
If properly monitored and treated, most pets recover smoothly from the surgery (the incision may only be 3-5 inches long, depending on the size of the pet). Life-threatening risks are low (but present, like with any surgery) in the hands of an experienced surgeon and properly prepared staff/facility; conversely, risks are fairly high in inexperienced and unprepared hands.
Parathyroid tumors are most commonly benign, and removal is usually curative.
When multiple glands are affected, the prognosis is less predictable, but the severity of the problems can often be markedly reduced.
Please schedule an appointment with our board-certified surgeon, Dr. Jeff Christiansen at the clinic of your choice, to evaluate your pet and to discuss options to improve your pet's or patient's length and quality of life.
If you have additional questions, please feel free to e-mail Dr. Christiansen directly.