7 mo MI Golden Retriever with signs of fibrous osteodystrophy (soft, deformed bones). Total and ionized calcium both low, serum phosphate high, PTH high. What is most likely cause of patient condition?

7 mo MI Golden Retriever with signs of fibrous osteodystrophy (soft, deformed bones). Total and ionized calcium both low, serum phosphate high, PTH high. What is most likely cause of patient condition?

• A. Consumption of all meat diet.
• B. Vitamin D3 overdose.
• C. Excess calcium diet.
• D. Chronic kidney disease.

Answer: (A)

The main idea here is nutritional secondary hyperparathyroidism from a calcium–phosphorus imbalance in a growing dog. When a young dog eats an all-meat diet, it’s often very high in phosphorus and low in calcium (unless bone content is included). This shifts the serum balance toward phosphate excess and calcium deficiency, so the parathyroid hormone (PTH) rises to try to correct it. The elevated PTH pulls calcium from bone and alters bone remodeling, leading to bone softening and replacement of normal bone with fibrous tissue. That process produces fibrous osteodystrophy with soft, deformed bones seen in this patient, along with the lab pattern of low calcium (total and ionized), high phosphate, and high PTH. Vitamin D3 overdose would push calcium higher, not lower, so it wouldn’t fit the labs. Chronic kidney disease can cause a similar mineral imbalance, but in a young puppy the dietary cause is the classic and most likely explanation given the history.

The main idea here is nutritional secondary hyperparathyroidism from a calcium–phosphorus imbalance in a growing dog. When a young dog eats an all-meat diet, it’s often very high in phosphorus and low in calcium (unless bone content is included). This shifts the serum balance toward phosphate excess and calcium deficiency, so the parathyroid hormone (PTH) rises to try to correct it. The elevated PTH pulls calcium from bone and alters bone remodeling, leading to bone softening and replacement of normal bone with fibrous tissue. That process produces fibrous osteodystrophy with soft, deformed bones seen in this patient, along with the lab pattern of low calcium (total and ionized), high phosphate, and high PTH.

Vitamin D3 overdose would push calcium higher, not lower, so it wouldn’t fit the labs. Chronic kidney disease can cause a similar mineral imbalance, but in a young puppy the dietary cause is the classic and most likely explanation given the history.