Naturally Occurring Secondary Renal Hyperparathyroidism and Fibrous Osteodystrophy in a Pet Rabbit (Oryctolagus cuniculus)

Rabbits with end-stage kidney failure often develop hypercalcaemia and osteosclerosis. Secondary renal hyperparathyroidism and fibrous osteodystrophy can be experimentally induced in rabbits through nephrectomy and a low-calcium:high-phosphorus diet, but clinical case reports are rare. A thin, mixed-breed, neutered male rescue rabbit was brought to a veterinary clinic due to lameness of the right hind limb and gait difficulties. Radiographs showed severe osteodystrophy. Additionally, there was a displaced, ununited simple fracture in the right mid-femur and a healed simple fracture in the right mid-tibia. Dentition was normal. The rabbit was euthanized. Blood tests revealed mildly elevated urea (12.3 mmol/mL), glucose (10.6 mmol/L), and alkaline phosphatase (179 mmol/L). High levels of serum parathyroid hormone (281.1 pg/mL) and a 25-hydroxyvitamin D concentration of 11.2 ng/mL were also noted. Creatinine was 105 µmol/L and inorganic phosphate was 1.53 mmol/L. Bone density in the mid-tibia was very low (934.6 mg/cm³). Tests for <i>Encephalitozoon cuniculi</i> antibodies were negative. Post-mortem examination showed severe chronic renal interstitial fibrosis and severe bilateral parathyroid hyperplasia. This case report highlights the novel finding that secondary renal hyperparathyroidism and fibrous osteodystrophy, accompanied by pathological fractures, can manifest as sequelae of end-stage renal disease in rabbits. This revelation is clinically significant and should be carefully considered by veterinarians when managing older rabbits presenting with fractures.