Thyrotoxicosis (Thyroid Storm)

Thyroid storm is a condition where there is an excessive increase of circulating thyroid hormone. This syndrome is typically seen in cats that have been previously diagnosed with hyperthyroidism.  Rarely dogs may experience thyrotoxicosis, usually this is seen in dogs with thyroid carcinoma or dogs that have been given a large overdose of thyroid supplement.  In cats there is often a precipitating event such as sudden cessation of hyperthyroid medication, after receiving radioactive iodine therapy, thyroid or parathyroid surgery, sepsis or dehydration. 

Increased circulating thyroid hormone can have a variety of effects on the rest of the organs in the body. It can cause an increase in the sensitivity of certain cells in the heart causing an increased heart rate, murmurs and arrhythmias. Some cats develop high blood pressure, ocular issues, abnormal mentation as well as increased respiratory rate and effort. In some cases cats will even have seizures or become comatose. Some other common symptoms are increased appetite, weight loss and hyperactivity. 

Diagnosis of thyroid storm is based on a history of clinical signs as well as identification of a precipitating event. Cats suspected of experiencing a thyroid storm should have a complete blood count, full blood chemistry with electrolytes, urinalysis and thyroid hormone testing. Most of these can be performed in the hospital, thyroid testing is usually sent to an outside laboratory. 

Treatment of thyrotoxicosis involves the use of medications such as methimazole (a medication used to treat hyperthyroidism) to control the production of thyroid hormone, counteracting the total body effects of the increased thyroid hormones, determining the precipitating factor as well as provide total body support. 

The key in treating thyrotoxicosis is early recognition and initiation of treatment.