Elevated Calcium (Hypercalcemia) Secondary to Hyperparathyroidism (Parathyroid Gland Tumor)

The clinical/medical problem of elevated calcium levels (hypercalcemia) has multiple differential diagnoses.  One of the most common and the only primary cause is the overproduction of the PARATHYROID HORMONE (PTH) that stimulates the balance of Calcium in the blood.  The usual cause is a functional parathyroid mass, typically an adenoma, which is benign but continues to produce parathyroid hormone.   As the functional mass continues to secret PTH, the influence on calcium elevation is unchecked by the normal “feedback” mechanism that is meant to control overproduction of any hormone.

Action of Parathyroid Hormone (PTH): Maintain Blood Calcium Levels

  1.  Increased calcium absorption and phosphorus excretion by the kidney
  2.  Increased calcium absorption in the intestinal tract
  3.  Increased calcium absorption from be one

Clinical Considerations Due to Elevated Calcium Levels:

  1.  Older (>10 years) dogs (some German shepherd and Keeshond breeds show prevalence)
  2. Increase thirst and urination (polyuria and polydipsia PU/PD)
  3. Variable – cystic calculi, loss of appetite, often normal and healthy?


  1.  Bloodwork – increased calcium levels with normal to increased PTH
  2.  Cervical (neck) ultrasonography to identify a mass of the thyroid gland
  3. Rule out other causes of hypercalcemia (lymphoma, carcinoma)
  4. Renal failure will elevate PTH but with no elevation in Ca++

Management of Parathyroid Gland Tumors:

The definitive treatment of parathyroid tumors is to surgically remove the tumor through a ventral cervical incision on the midline between the two thyroid glands.  In the case of severe hypercalcemia preoperatively, it might be necessary to increase urine output (diuresis) prior to anesthesia as well as the use of cortisone therapy.  In most every case of primary hyperparathyroidism, only one of the four PTG’s (parathyroid glands) are involved.  In fact, the other glands will be atrophied and suppressed by the excessive PTH.  The surgery involves delicate dissection of the affected gland with partial removal of the thyroid gland if necessary.  All four PTG’s are assessed at the time of surgery.  The surgery is usually very successful in finding and removing the affected PTG.  Hemorrhage is a minimal problem.  The affected gland and surrounding tissue is submitted for pathology to confirm the diagnosis and to rule out any malignancy.  The sutured surgical site typically heals very well because of the location.

Postoperative Management of PTG Tumors:

Hypocalcemia (low calcium) becomes a concern after surgery because the negative feedback mechanism for calcium regulation is now altered and the other 3 glands because of suppression are NOT producing PTH immediately.   Postoperatively, both Calcium and Vitamin D supplementation is recommended with blood Calcium levels checked at 3 – 5 days postop. Severe low calcium can result in an emergency situation.  The owner should be very observant for any signs of loss of appetite, facial tremors or seizures and have the patient seen immediately.  Severe hypocalcemia has to be treated with intravenous calcium until signs subside.  The period of time for hypocalcemia can vary to as long as 3 weeks postoperatively.  Once at least 2 successive blood calcium levels are normal, the patient can be deemed safe from the fear of hypocalcemia problems.  The prognosis following PTG tumor removal and patient recovery and return to normal calcium levels is very good.  Once the period of hypocalcemia concern has passed and the remaining parathyroid glands are functioning normally, the owner can return their dog (or cat) to full normal activity without fear of problems.