Clinical Exposures: An incidental finding of primary hyperparathyroidism in a dog

Jul 01, 2004
By staff

Figure 1 & 2. Lateral and ventrodorsal abdominal radiographs demonstrating radiopaque areas in both renal pelves (arrows).
A 12-year-old, 18.4-lb (8.4-kg) neutered male Lhasa apso was referred to Mississippi State University's Animal Health Center for evaluation of hypercalcemia. The referring veterinarian had discovered the marked hypercalcemia on a preanesthetic profile before a dental prophylaxis. The dog was eating Prescription Diet u/d (Hill's) to prevent recurrence of calcium oxalate uroliths after surgical removal three years before.

Physical examination and diagnostic tests

Figure 1 & 2. Lateral and ventrodorsal abdominal radiographs demonstrating radiopaque areas in both renal pelves (arrows).
The only abnormality identified on physical examination was a 2-cm palpable mass adherent to the region of the left thyroid gland. The results of a complete blood count were normal. A serum chemistry profile revealed hypercalcemia (16 mg/dl; normal = 8.8 to 11.2 mg/dl), a normal phosphorus concentration (2.8 mg/dl; normal = 2.6 to 5.7 mg/dl), elevated alkaline phosphatase activity (449 U/L; normal = 11 to 140 U/L), and a mildly elevated blood urea nitrogen concentration (31 mg/dl; normal = 8 to 24 mg/dl). The dog's urine specific gravity was 1.013, which was attributed to hypercalcemic effects on the kidneys (e.g. mineralization of the renal tubule basement membranes, renal tubule degeneration, and interstitial fibrosis) or nephrogenic diabetes insipidus (i.e. inhibition of antidiuretic hormone effects on renal blood flow at the collecting ducts).

Figure 3. A longitudinal ultrasonogram of the left lateral cervical region. A suspected parathyroid mass (2.1 x 0.8 cm) is evident (arrows).
The results of a thoracic radiographic examination were normal, but an abdominal radiographic examination revealed staghorn-shaped mineral opacities in both renal pelves (Figures 1 & 2). An ultrasonographic examination of the dog's cervical region showed a 2.1-x-0.8-cm hypoechoic mass that was suspected to be associated with a parathyroid gland (Figure 3). Additional testing included measuring the intact parathyroid hormone (PTH), PTH-related protein, and ionized calcium concentrations (Table 1).

Diagnosis and treatment

Table 1 PTH, PTH-related Protein, and Ionized Calcium Concentrations
All of the findings were consistent with primary hyperparathyroidism, including the elevated ionized calcium, high normal PTH, and undetectable PTH-related protein concentrations. Although the PTH concentration was normal, it was determined to be inappropriate for the high total serum calcium and ionized calcium concentrations. We decided to perform surgery to remove the affected parathyroid gland.

Figure 4. An intraoperative photograph of the left intracapsular parathyroid gland (cranial is to the left, and lateral is toward the top). The trachea is visible at the bottom of the photograph.
The dog was admitted to the intensive care unit for intravenous diuresis with 0.9% saline solution (120 ml/kg/day) for 12 hours before surgery. We also prescribed calcitriol (20 ng/kg/day orally for three days, followed by a maintenance dose of 5 ng/kg/day).1

Figure 5. The excised left intracapsular parathyroid gland.
Hydromorphone was given intravenously as a preanesthetic before induction with propofol. Anesthesia was maintained during the surgery with isoflurane in oxygen. At surgery, the left intracapsular parathyroid gland was grossly enlarged, so it was excised (Figures 4 & 5). The excised tissue was submitted for histopathologic examination, which later confirmed our presumptive diagnosis of primary hyperparathyroidism (i.e. parathyroid [chief cell] hyperplasia).

After surgery, the dog was monitored in the intensive care unit for signs of hypocalcemia such as tremors, facial pruritus, restlessness, and seizures. The total serum calcium concentration was measured every 12 hours. Oral calcium supplementation (calcium carbonate, 25 mg/kg/day) was prescribed to help prevent a hypocalcemic crisis. The calcium concentrations remained normal, so the dog was discharged from the hospital four days after surgery. The owners were instructed to watch for any signs of hypocalcemia. Because of the morbidity associated with nephrolith removal, the owners were advised that removal would not be warranted unless the dog exhibited problems referable to the nephroliths.

The calcium and calcitriol were gradually tapered by the dog's regular veterinarian over two months. At the three-month checkup, the dog was normocalcemic, nonazotemic, and clinically asymptomatic.