A challenging case: Primary hyperparathyroidism in a dog

Ultrasonographic examinations helped identify the source of this dog's persistent hypercalcemia.
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Aug 01, 2009


Vital Stats
An 8-year-old 50.6-lb (23-kg) neutered male Airedale terrier was presented to Forest Hill Animal Clinic for a wellness examination and laboratory tests. The dog was receiving levothyroxine (300 µg orally every 12 hours) for previously diagnosed hypothyroidism, and tylosin (200 mg orally every 12 hours) and Prescription Diet i/d Canine (Hill's Pet Nutrition) for chronic colitis of four years' duration. The dog also had a history of chronic arthritis and had received meloxicam in the past.

HISTORY

Five months before the wellness examination, the dog had been presented to a veterinary emergency clinic for evaluation of lethargy of one day's duration. The dog's vital signs were normal. An electrocardiogram (ECG) had been obtained, and the results were normal. A serum chemistry profile had revealed that the total calcium concentration was 3.1 mmol/L (reference range = 2.2 to 3 mmol/L). The albumin concentration was normal. The parathyroid hormone (PTH) concentration had been measured because of the increased calcium concentration, and it was normal (3.9 pmol/L; reference range = 3 to 17 pmol/L). The patient had been discharged 48 hours after receiving intravenous fluid therapy and supportive care.

PHYSICAL EXAMINATION AND LABORATORY FINDINGS

A physical examination at Forest Hill Animal Clinic revealed mild dander, a dry coat, and ceruminous debris in both ears. Complete blood count (CBC) results were normal, and results of a heartworm antigen test were negative.

Further testing revealed a total calcium concentration of 3.5 mmol/L, with an ionized calcium concentration of 1.82 mmol/L (reference range = 1.25 to 1.45 mmol/L), a PTH concentration of 4 pmol/L, a nonmeasurable parathyroid hormone-related peptide (PTHrP) concentration, and a normal vitamin D concentration (120 nmol/L; reference range = 60 to 215 nmol/L).

The owner indicated that the dog had not been exposed to toxins, including vitamin D supplements or creams. The dog was then referred to a referral center in Toronto for further evaluation of persistent hypercalcemia.

REFERRAL HOSPITAL PATIENT EVALUATION

Results of another CBC and serum chemistry profile revealed a total calcium concentration of 3.5 mmol/L. The dog's free T4 concentration was normal (31.9 pmol/L; reference range = 16 to 45 pmol/L). A urinalysis revealed a specific gravity of 1.005, 10 to 20 calcium oxalate crystals/hpf, and bacteriuria. Aerobic bacterial culture of the urine was positive for Escherichia coli, which was sensitive to enrofloxacin.

Diagnostic imaging to help determine the underlying cause of the hypercalcemia was performed. Thoracic radiography revealed no abnormalities, but abdominal ultrasonography documented multiple cystic calculi and mild renal pelvic mineralization. Cervical ultrasonography to assess the parathyroid glands revealed no abnormalities.

Differential diagnoses for the dog's hypercalcemia included lymphoma, leukemia, multiple myeloma, primary hyperparathyroidism, and, less likely, excessive vitamin D consumption (because of the normal vitamin D concentration). Surgery to remove the cystic calculi was scheduled for the next day.