Renal Osteodystrophy Associated with Juvenile Nephropathy in a 6-month-old Labrador Retriever

Renal secondary hyperparathyroidism is a common sequela of chronic renal failure in the dog, but is not commonly observed in juvenile patients. A 6 month old female Labrador retriever with juvenile nephropathy and associated renal osteodystrophy is presented. Older dogs with this condition typically have highly pliable facial bones due to increased parathormone-induced osteoclastic activity subsequent to progressive hyperphosphatemia and decreased serum ionized calcium. The pathogenesis in this dog is similar with reduced glomerular filtration rate causing pronounced hyperphosphatemia [23 mg/dL (2.5-5)], decreased ionized calcium [0.58 mmol/L (1.25-1.45)], and increased parathormone levels [62.0 pmol/L (0.5-5.8)]. Other abnormalities included marked renal azotemia [BUN 171 mg/dL (8-24), creatinine 5.5 mg/dL (0.5-1.4)], isosthenuria (urine specific gravity 1.009), hypocalcemia [6.1 mg/dL (8.8-11.2)], and anemia [HCT 14.4% (34-60)]. Many cases of juvenile nephropathy also show concurrent signs due to decreased formation of calcitriol, which may include predisposition towards fibrous osteodystrophy and rickets. The osseous lesions in this case were limited to the facial bones which were markedly firm and swollen due to hyperostosis and fibrous osteodystrophy. 25-hydroxyvitamin D was within normal limits [106 nmol/L (60-125)]. The lesions are typical of a familial nephropathy, which is suspected in this case. Such disorders have not been described in the Labrador retriever and an individual renal developmental disorder cannot be excluded. The dog was fed a commercial dog food and no familial history of renal disease was reported. Nutritional secondary hyperparathyroidism is more common in juvenile dogs but presents with progressive lameness and long bone abnormalities. Vitamin D-dependent rickets, type I and type II, was also considered as a differential diagnosis but was also excluded. Poster #2, Clinical Case Report/Series