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Answers and Discussion

Case #20 -- Parathyroid Adenoma

Answers and Discussions to the Questions:

What clinical signs do you see with hyperparathyroidism?

Polyuria and polydipsia occur due to inhibition of ADH. The owner may complain of muscle weakness, stiff gait, lethargy, seizures, anorexia, vomiting or constipation.

What are the differentials for hypercalcemia?

Differentials include hyperparathyroidism, hypoadrenocorticism (Addison's), renal failure, vitamin D toxicosis, osteolytic lesions (neoplasia, osteomyelitis), neoplasia and lab error.

What diagnostics should you perform to rule out your differentials?

Look everywhere for cancer: chest and abdominal radiographs, palpate lymph nodes for signs of lymphoma, rectal exam for anal sac adenocarcinoma, palpate long bones for osteosarcoma. Chemistry panel can help rule out renal failure and Addison's. A PTH assay can be done for hyperparathyroidism, but may still be normal in the face of underlying parathyroid disease, in which case a surgical explore of the neck is warranted.
What medical treatment would you do while waiting for surgery (surgical explore of the neck)?

Normal saline would be the fluid of choice with potassium chloride added as needed--diurese as necessary. Furosemide will aid in calcium excretion (2 mg/kg BID, IV or orally). Do not use thiazide diuretics--they reduce calcium excretion! Usually this is enough to control hypercalcemia. However, if more aggressive therapy is needed, calcitonin may be used to inhibit bone resorption (4-6 IU/kg BID, SQ or IM). Steroids may also be used to decrease bone resorption and increase calcium excretion, but they should not be used until a diagnosis has been obtained since lymphoma is one of the most common causes of hypercalcemia.

What should you monitor after surgery (parathyroidectomy)?

Monitor serum calcium daily or more often if signs warrant. Watch for signs of hypocalcemia: muscle tremors, twitching of the whiskers, seizures, stiff gait, ataxia, weakness and lethargy. If calcium starts to fall past low normal, start calcium carbonate (50-75 mg/kg/day PO divided TID-QID). Monitor serum calcium at least weekly during oral calcium therapy. Have the owner stop calcium therapy if signs of hypercalcemia develop. Calcium supplementation can be decreased over time to see how the patient adjusts.

Follow-Up: Exploratory surgery of the neck revealed the right caudal parathyroid gland was firm and enlarged. It was removed and diagnosed to be parathyroid adenoma. "Henry's" serum calcium level became normal after surgery. He did not need any calcium supplementation and was released a few days later.

Parathyroid Adenoma Pearls

Hypercalcemic patients may present with PU/PD, vomiting, constipation, muscle weakness, stiff gait or seizures.
Diagnostics should include bloodwork, a cancer search, a parathormone assay and possibly exploratory surgery.
After removing the parathyroid glands, watch the patient for signs of hypocalcemia and treat with calcium supplementation if necessary.