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Rubber jaw syndrome is caused by hyperparathyroidism due to renal failure. The parathyroid glands are activated because of a reduction of calcium in the blood. In addition, the PTH causes the calcium to be absorbed into the intestine and consequently, the inability to activate Vitamin D3. Because of the lost calcium, the bone gets replaced by fibrous tissue and this makes the bones weak. It is most often caused by secondary hyperparathyroidism since primary hyperparathyroidism is a disease that originates in the parathyroid gland itself from adenoma or neoplasia. It is more common for dogs to have secondary hyperparathyroidism caused by renal failure. The amount of deformity depends on the length of time the kidneys have not been functioning right and how severe the disease is.
Rubber jaw syndrome (renal osteodystrophy) is a condition of excess parathyroid hormone caused by kidney disease. The kidneys are unable to excrete the parathyroid hormone, which causes a buildup of these hormones in the body. The craniofacial bones (jawbones) are most often affected and it creates a severe deformity of the facial bones and softening of the jawbones, making the jaw rubbery. This may be caused by primary hyperparathyroidism or secondary hyperparathyroidism. The early symptoms include depression, frequent urination, and increased thirst. If these signs are missed, the deformity of the facial bones will soon be obvious enough to warrant a trip to the veterinarian.
Some of the symptoms of rubber jaw syndrome include:
Certain breeds are more susceptible than others. Some of them include large and giant breed dogs that grow rapidly such as:
To diagnose rubber jaw syndrome, your veterinary care provider will need to perform a complete and thorough physical examination even if your dog has obvious deformities and softening of the jaw. The veterinarian will also need to run some diagnostic tests. Some of the tests should include x-rays to check the bones. If your dog has rubber jaw syndrome, this will show up on x-rays as fibrous tissue rather than bone and there may be holes throughout your dog’s skeleton. In addition, an ultrasound or CT scan will show the kidneys are shrunken and have lesions. Blood tests will most likely indicate excess calcium and parathyroid hormones. The veterinarian may also take a biopsy of the kidneys to determine the cause of kidney disease or failure.
Treatment options for rubber jaw syndrome caused by renal secondary hyperparathyroidism include management of the renal disease, medication, and changes in diet.
Treatment of Renal Disease
Treatment of the renal disease should be taken care of first. However, if the kidneys are already too damaged, dialysis and a kidney transplant may be the only choice. However, kidney transplants are rarely successful because of the unique immune system in dogs. The donor would have to be a relative of your dog and they both must be young and otherwise healthy.
Calcitriol (vitamin D3) should be given intravenously to regulate the blood levels of calcitriol before using oral supplements. Antibiotics may also be given if the veterinarian suspects a kidney infection. Your dog may also need fluids and oxygen therapy so your veterinarian will probably recommend a brief hospital stay.
Changes in Diet
Phosphorous binding supplements (aluminum hydroxide, calcium carbonate, or sevelamer hydrochloride) to control the phosphorous levels absorbed in the intestines. A diet high in Vitamin D3 and low in phosphorous should be followed for the remainder of your dog’s life.
If your dog’s hyperparathyroidism is not treated right away, she may end up with irreversible kidney failure and that leads to a shortened life span. Your dog’s creatinine, phosphorous, serum calcium, and parathyroid hormones will need to be monitored during treatment. These tests should be done once a week for several weeks and then once per month for six months. This is essential to prevent hypercalcemia. The veterinarian will then need to run blood tests every six weeks for about one year. Your dog can lead a fairly normal life and prognosis is moderate depending on the severity of the disease.
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