Parathyroid Tumors
Tumors affecting the parathyroid glands are rare in dogs and cats, but are known to occur. The most common tumor affecting the parathyroid gland is a benign tumor called an ademona. The tumor most frequently arises from one of the four parathyroid glands in the neck. However, tumors can be present in multiple glands simultaneously in approximately 10% of patients. Genetics have been associated with tumor development. Keeshonds have a known genetic predisposition to the problem. Other high risk breeds include Labrador Retrievers, German Shepherds and Siamese cats. Parathyroid tumors are locally aggressive, but they do not spread.
Symptoms:
Symptoms of parathyroid tumors usually result from high calcium levels in the blood. Many dogs begin by drinking more water and urinating larger volumes more frequently. As the tumor grows and the blood calcium level rises, many patients become weak in their rear legs and some lose their appetite. Calcium bladder stones develop in a number of patients due to prolonged high blood calcium levels. In these patients, the only sign may be straining to urinate, stranguria, or a complete inability to urinate when a bladder stone gets stuck in the urethra.
Testing:
Blood work often reveals high blood calcium and a normal to low phosphorus level. The kidney values may also be increased in some patients. Urine results are variable but often show poor concentration ability and occasional calcium oxalate crystals.
Special blood tests can be submitted to test parathyroid hormone directly and another blood factor called parathyroid hormone related protein (PTHrp). The parathyroid hormone level is often elevated, but a normal parathyroid hormone level does not exclude the disorder. The PTHrp level helps to differentiate other types of cancer as the cause of the high blood calcium.
X-rays are often unrewarding in the diagnosis of parathyroid tumors, but are important for excluding other causes of high blood calcium, namely other cancers. X-rays may be helpful n identifying bladder stones, but not all stones are easily seen on x-rays.
An ultrasound, or sonogram, of the neck is the preferred method to directly see the parathyroid gland and to determine how many glands are involved. On the ultrasound, one of the glands is generally two to three times larger than the others and is often very dark in color. Occasionally, more than one gland is enlarged.
Treatment:
Surgical removal of the enlarged parathyroid tumor is ideal and is by far the most effective. However, some owners prefer not to pursue surgery because it is invasive. Ethanol ablation is procedure where a very concentrated alcohol solution is injected into the tumor with the guidance of ultrasound. Although not as effective as surgery in some patients, the procedure can be performed without an incision. Ethanol ablation is most effective for single large tumors. Patients with tumors in multiple glands are better treated surgically. A hoarse bark is occasionally noted after an ethanol injection, but typically resolves within a few days.
Regardless if surgery or ethanol ablation is performed, patients generally need to be hospitalized for 3-7 days after the procedure to carefully monitor their calcium levels. If the blood calcium level drops too quickly and is not immediately treated, it can result in a life threatening emergency. Some patients may need to start medications prior to the procedure to limit the chance of low blood calcium which is also known as hypocalcemia.