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Excess Thyroid Hormone in Dogs



Outpatient management is usually sufficient if drugs that inhibit the production of thyroid hormones can be used. In cases where the thyroid is overactive as the result of medications given for hypothyroidism, which is more common in dogs, the medication dosage can be adjusted and the symptoms will generally diminish.


Surgical removal of the thyroid gland, or treatment using a radioactive form of iodine will require inpatient treatment and monitoring. Surgical removal of the thyroid gland is best performed when only one thyroid gland is affected, as removal of both can possibly lead to hypothyroidism. Another complication that can occur after surgical removal of the affected thyroid gland is the successive hyper-activity of the remaining thyroid gland.


If the hyperthyroidism is related to a tumor of the thyroid, the option for surgery will be dependent on the invasive nature of the tumor. The proximity of the tumor to the esophagus and major arteries can make surgery difficult, or even impossible, but in some cases a portion of the tumor may be removed, and the the dog can be treated further with radioactive therapy. The prognosis is dependent on how far the tumor has metastasized into the surrounding tissues.


The use of radioiodine is restricted to a confined medical facility, since the treatment itself is radioactive. Depending on the state in which you live and the guidelines in place, your dog will need to be hospitalized from several days to a few weeks after being treated with radioactive medicine, to allow the radioactive material to clear most of the body before the dog can be handled by family members. Precautions will still need to be taken after taking your dog home, to reduce your risk of having a toxic reaction to the radioactive treatment. Your veterinarian will advise you in precautionary measures.


Once the major symptoms resulting from excessive levels of thyroid hormones in the body have been resolved, dietary modifications often do not need to be strictly enforced. Even so, dietary modifications may be necessary to treat or control complications that can occur in conjunction with hyperthyroidism, such as kidney damage.


Living and Management


Once treatment has begun, your veterinarian will need to reexamine your dog every two to three weeks for the initial three months of treatment, with a complete blood count to check for serum thyroid hormone concentration of T4. The dosage of the medications will be adjusted to maintain T4 concentration in the low-normal range.


If your dog has had surgery, particularly removal of the thyroid gland, your veterinarian will want to closely observe the dog's physical recovery. Development of low blood-calcium levels and/or paralysis of the voice box during the initial postoperative period are complications that will need to be watched for and treated, should they occur. Your doctor will also be measuring thyroid hormone levels in the first week after surgery and every three to six months thereafter, to check for recurrence of thyroid gland over activity.


In cases in which a tumor of the thyroid is found, the prognosis will be dependent on whether it is malignant or benign. Malignant tumors of this type often metastasize quickly into the surrounding tissues and organs, making treatment difficult and prognosis poor. Benign tumors can generally be managed, and have a much better prospect for future health. 


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