Low Thyroid & Seizures in Dogs


Hypothyroidism is a relatively common disease affecting dogs; this condition occurs when the thyroid gland does not produce enough thyroid hormones. Most cases of hypothyroidism are caused by the body's own immune system attacking the cells of the thyroid gland; however, cancer and other diseases, as well as the use of some medications and even genetic cases, have been recorded.


Thyroid hormones are needed by all organ systems of the body for normal cell metabolism. For this reason, the signs and symptoms can vary greatly from case to case. There are some classic signs that may point your veterinarian in the right direction; these may include weight gain, lethargy, hair loss, changes in skin pigment and high blood cholesterol. In addition to these classic signs, hypothyroidism can also cause behavior changes (aggression, passivity) and hyperactivity. Some veterinarians believe that hypothyroidism can also cause seizures.

The Seizure Connection

The connection between seizures and hypothyroidism is still a relatively new concept for many veterinarians; however, in an analysis of 499 cases by an independent neural network correlative statistical program, results showed a "significant relationship between thyroid dysfunction and seizure disorder and thyroid dysfunction and dog-to-human aggression." In addition, in a study conducted by Dr. Jean Dodds, DVM and Drs. Nicholas Dodman, Linda Aronson and Jean DeNapoli of Tufts University School of Veterinary Medicine, of 634 dogs, 63 percent showed abnormal thyroid function with 77 percent of these dogs showing seizure activity. Due to the results of these studies, it is imperative that veterinarians routinely test for hypothyroidism when presented with a dog displaying seizure activity.

Blood Tests

There is some controversy among veterinarians regarding the role of hypothyroidism as the cause of seizures and the benefit of blood tests. Unfortunately, there has been little research that forms any real conclusions. In one particular study, the results indicated that dogs taking Phenobarbital may present with lower blood serum levels of T4 (a marker in blood used to diagnose hypothyroidism), which may lead the veterinarian to diagnose the condition in an otherwise healthy dog. Many dogs have borderline thyroid levels and are considered to be normal; however, dogs that present with other classic signs of hypothyroidism along with seizure activity should be considered to be hypothyroid when their blood levels are borderline.


Due to the unreliability of blood tests, it is suggested that dogs displaying signs of hypothyroidism, and a low or borderline test result, in conjunction with seizure activity be placed on a trial of Soloxine (used in the treatment of hypothyroidism) for six weeks; if the symptoms improve, then the dog is probably hypothyroid; if no changes occur, it can be assumed that the cause of the seizure activity is not hypothyroidism.


Although a definitive answer has not yet been determined, there is enough evidence to suggest that some dogs with hypothyroidism may present with seizure activity. As researchers continue to study the connection; it is expected that more cases will be diagnosed.

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