Bobby, a 10-year-old male neutered large crossbreed, presented with a several-week history of lethargy, weakness and tremors.
His physical examination was relatively unremarkable, so Dr Ferran recommended blood tests. Haematology did not reveal any significant abnormalities, but biochemistry showed a markedly elevated total calcium concentration.
Hypercalcaemia can cause a wide range of clinical signs, including those seen in Bobby. It can also cause increased thirst and urination and may lead to urolithiasis and associated urinary signs.
When investigating hypercalcaemia, it’s useful to determine whether ionised calcium is also elevated, as it was in Bobby’s case. Some conditions can cause an increase in total calcium without affecting ionised calcium, so measuring ionised calcium can help narrow down the potential causes.
A handy mnemonic we use to remember the different causes of hypercalcaemia is ‘HOGS IN YARD’. (Click on image to download.)
In Bobby’s case, our main differentials were primary hyperparathyroidism and neoplasia.
Primary hyperparathyroidism typically affects older dogs and occurs when the parathyroid gland produces excessive parathyroid hormone (PTH), resulting in increased blood calcium. Diagnosis is based on identifying an inappropriate PTH concentration in the presence of hypercalcaemia.
Tip: A normal PTH does NOT rule out primary hyperparathyroidism!
Neoplasia can cause hypercalcaemia through several mechanisms, including the production of PTH-related protein (PTHrP), cytokine production and osteolysis. PTHrP can be measured, although testing availability can be limited. Diagnostic imaging can therefore play an important role in investigating an underlying neoplastic process. Lymphoma and apocrine gland anal sac adenocarcinoma are among the neoplasms more commonly associated with hypercalcaemia.
Bobby’s investigations
Bobby underwent:
- Bicavitary imaging: thoracic radiographs and abdominal ultrasound to investigate for evidence of neoplasia.
- PTH measurement: to help confirm or exclude primary hyperparathyroidism.
- Ultrasound of the neck: to look for a parathyroid nodule while awaiting the PTH results, which can take several weeks.
Pleasingly, Bobby’s thoracic and abdominal imaging was unremarkable. However, ultrasound of his neck revealed a large parathyroid nodule (see image), supporting a diagnosis of primary hyperparathyroidism.
Bobby subsequently underwent surgery and recovered very well, without complications.
Several weeks later, his PTH result returned and was markedly elevated, further supporting the diagnosis of primary hyperparathyroidism.
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