Due to the subtle nature of most symptoms of hyperthyroidism in felines, and the tendency for onset to occur in middle or old age, many mistake this condition for normal aging rather than a serious disease. Unfortunately, this means that many owners leave feline hyperthyroidism untreated which can cause pain and anguish for the afflicted cat, even death. However, feline hyperthyroidism is completely treatable once diagnosed and all painful symptoms can be managed or avoided entirely.

What is Hyperthyroidism in Cats?

Put simply, hyperthyroidism is an overactive thyroid. The thyroid is the gland which controls your cat’s metabolism, just like in humans. In addition, the thyroid hormones affects nearly all organs throughout your cat’s body and therefore thyroid disease can cause serious secondary conditions. Hyperthyroidism is the most common glandular disorder among cats, particularly middle and older cats. In fact, less than six percent of cases are younger than ten years old with the average onset occurring between 12 and 13 years. The condition is most often caused by an excessive concentration of circulating thyroxine, a specific thyroid hormone better known as T4, in the bloodstream. However, enlarged thyroid glands can also increase T4 levels and may be the result of tumors, either malignant or benign.

Symptoms of Hyperthyroidism in Cats

Weight loss and increased appetite are two of the most prevalent symptoms of hyperthyroid cats due to an increased metabolic rate. Weight loss is seen in 95 to 98 percent of cases, while appetite changes are seen 67 to 81 percent of the time. Other common symptoms include excessive thirst, increased urination, increased energy or nervous behavior, unkempt appearance, panting, diarrhea, and increased shedding.

Secondary Problems

Because the thyroid gland and its hormones affect nearly every organ in the rest of the body, hyperthyroidism can cause secondary medical problems including heart disease and high blood pressure. Elevated thyroid hormone levels provoke an increased heart rate and stronger contraction of the heart muscle. If left untreated, this change may become the heart’s new normal and could eventually lead to heart failure as extra strain wears on the heart. However, once the underlying hyperthyroidism is addressed, the cardiac changes will likely improve or even completely resolve.

Hypertension, or high blood pressure, is another potential complication and can cause additional damage to several organs including the eyes, kidneys, heart, and brain. Drugs may be prescribed to help mitigate hypertension until the hyperthyroidism is controlled. Like cardiac changes, hypertension will improve or resolve once the underlying condition is treated.

Diagnosis of Hyperthyroidism

Hyperthyroidism can only be determined by a veterinary professional because several common diseases among older cats – diabetes, inflammatory bowel disease, intestinal cancer, and chronic kidney disease  – share similar symptoms and a battery of tests will be required for a definitive diagnosis. A complete blood count (CBC), chemistry panel, and urinalysis can help rule out diabetes and kidney disease. Hyperthyroidism may show normal results on a CBC and urinalysis, but the chemistry panel will often display elevation of several liver enzymes.

If your veterinarian suspects hyperthyroidism, he may choose to immediately utilize a blood test to diagnose. Simple blood tests will show elevated T4 levels in the bloodstream, confirming hypothyroidism. Unfortunately, between two and ten percent of cats with hyperthyroidism will have normal T4 levels. This could be due to a concurrent illness lowering T4 levels or natural fluctuation.

Hyperthyroidism Treatment

When it comes to treatment of hyperthyroidism, hyperthyroid cats have several options. Your veterinarian will work with you to decide what the best treatment plan is for you and your cat. In general, those treatment options include:

• Drug Therapy: Methimazole has been the longtime oral drug treatment for feline hyperthyroidism. It is highly effective in correcting the condition and may produce results as quickly as two to three weeks. However, as with all drugs, there are some adverse potential side effects such as loss of appetite, vomiting, lethargy, blood clotting disorders or liver problems. Methimazole treatment method will also require lifelong daily administration of the medication and T4 levels will need to be rechecked regularly.
• Surgical Intervention: If your cat’s hyperthyroidism is caused by the presence of a tumor, your veterinarian may suggest surgically removing the afflicted portion of the thyroid. While surgery may seem like the costly option, it is often less expensive than years of oral medication and regular blood work.
• Radioactive Iodine Therapy: This may be the safest and most effective treatment option. Radioactive iodine is injected into the thyroid gland where it eradicates and destroys the hyperfunctioning tissue. Typically, only one treatment is needed to cure the condition. However, it is a costly procedure at about $500-800 per injection.

Treating your cat’s hyperthyroidism effectively is important for their continued health and comfort. As mentioned before, untreated feline hyperthyroidism can cause your cat painful symptoms and secondary problems which put your cat’s life at risk. However, once treated it is a manageable condition and your cat can be expected to live a normal, happy life.