FINAL DIAGNOSIS: Renal Dysplasia in a Lhasa Apso
History: A 3.5 year old neutered male Lhasa Apso with a one-week history of lethargy and anorexia was submitted for necropsy to the Purdue Animal Disease Diagnostic Laboratory. The serum chemistry revealed increase in BUN (142 µg/dl), creatinine (7.8 µg/dl), phosphorus (10.2 µg/dl) and normal calcium (10.2 (µg/dl). Ultrasound examination revealed small kidneys. Upon poor prognosis, the animal was euthanized and submitted for necropsy.
Gross findings: Both kidneys were misshapen, shrunken, modular with diffusely pitted surfaces. The renal weight was 0.18% of the body weight. Both external parathyroid glands were red, smooth and enlarged. The mandibles of this dog were flexible and could be easily deviated laterally in either direction ("rubber jaw"). The ribs and calvarium were thin, brittle and prone to fracture upon applying pressure.
Histopathologic findings: The cortex and medulla in both kidneys were variably shrunken and often replaced by linear bands of fibrosis that surrounds and replaces tubules, glomeruli, and vessels and extends into the medullary interstitium. Rare glomeruli are reduced in size and contain closely packed hyperchromatic nuclei (fetal or immature glomeruli). Multifocally, the collecting tubules in the medulla were dilated, lined by epithelium with a scant amount of cytoplasm and hyperchromatic nuclei (primitive or immature tubules) and surrounded by loose and poorly differentiated stroma (mesenchyme). In addition, rare tubules in the medulla had adenomatous differentiation (resembling acini) of the epithelium. Mineralization, necrosis and regeneration of the tubular epithelium were present. The parathyroid glands were diffusely hyperplastic. Most of the mature bone in the mandibles and sinuses was fragmented and replaced by sheets of fibrous connective tissue admixed with numerous scattered osteoclasts. Occasionally, osteoid lined by osteoblasts was seen (new bone formation). The morphologic diagnoses were renal dysplasia, parathyroid hyperplasia and fibrous osteodystrophy of the mandible.
Discussion: Renal dysplasia is defined as disorganized development of renal parenchyma due to abnormal differentiation, i.e., presence of inappropriate structures for specific developmental stage of the animal or development of anomalous structures. Abnormal metanephric differentiation and nephrogenesis is due to failure or incomplete interaction between the ureteric bud and metanephric blastemia. In dogs, the lesions associated with renal dysplasia include fetal/immature glomeruli and/or tubules, adenomatoid tubular epithelium, persistent mesenchyme and metanephric ducts. A definitive diagnosis of renal dysplasia in this dog was made based on the presence of fetal glomeruli, primitive tubules and persistent mesenchyme. This condition is reported to have hereditary predisposition in Golden retrievers, Shih Tzus, Boxers, Finnish harriers, Dutch Kooiker, Cocker spaniels and Lhasa Apsos. Unfortunately, in this dog, no familial history was submitted.
Fibrous osteodystrophy is due to hyperparathyroidism secondary to renal dysfunction. Persistent hypocalcemia (due to kidney dysfunction) causes continued stimulation of parathyroid hormone resulting in parathyroid chief cell hyperplasia (renal secondary hyperparathyroidism). Parathyroid hormone acts primarily on bone and kidney by stimulating bone resorption and calcitriol production, respectively. Continuous bone resorption by osteoclasts results in characteristic marked softening of bones and replacement with fibrous connective tissue (fibrous osteodystrophy).
The prognosis in animals diagnosed with renal dysplasia is poor. Affected dogs can be maintained for some duration on supportive treatments. Careful breeding by avoiding carrier animals should be of help in limiting this disease.
-by Dr. Vimala Vemireddi, ADDL Graduate Student