parathyroid TUMORS

BACKGROUND

Parathyroid tumors are uncommon in dogs and very rare in cats. The majority of parathyroid tumors are benign (ie, hyperplasia or adenoma) and involve a single gland. Up to 10% involve multiple parathyroid glands. Parathyroid tumors result in increased production of parathyroid hormone which causes hypercalcemia (increased calcium levels in the blood). Hypercalcemia is responsible for the clinical signs of polyuria (increased urination) and polydipsia (increased drinking), as well as weakness, poor appetite, and calcium oxalate bladder stones causing lower urinary tract disease.

DIAGNOSIS

Primary hyperparathyroidism is confirmed with simultaneous increases in both calcium and parathyroid hormone levels. These blood tests are sent to a specialist laboratory. Ultrasound of the neck can also be used to support the diagnosis, but ultrasonographic findings correlate with surgical findings in only 76% of dogs because parathyroid tumors are often small (< 1.0 cm) and can be difficult to detect with ultrasound.

CLINICAL STAGING

Blood tests and abdominal radiographs or ultrasound are required for clinical staging to determine if hypercalcemia has resulted in damage to the kidneys or the development of bladder stones.

TREATMENT

Surgical excision of the parathyroid tumor is recommended. Alternative treatment options include ultrasound-guided intralesional treatment with either ethanol injection or radiofrequency heat ablation.

PROGNOSIS

The prognosis is excellent following surgical excision. In one clinical study (2007) comparing the three treatment options in 110 dogs, hypercalcemia was controlled in 94% of 47 dogs treated with parathyroidectomy, 90% of 49 dogs treated with radiofrequency heat ablation, and 72% of 18 dogs treated with ethanaol ablation. Calcium levels decrease during the first 24 hours and then normalize over 1-7 days. Vitamin D and/or calcium supplementation may be required in the short- or long-term depending on the ionized calcium status at 24 hours postoperatively.