Hyperthyroidism in cats: an overview
Author: Luana A. Battaglia, Ilona Judhianto und Stefanie Stobbe | Read time: 9 min
Hyperthyroidism is a common hormonal disorder that affects cats from 8 years onwards. Here, the thyroid – a gland located just below the throat – produces an excessive amount of thyroid hormones resulting in an increased metabolic rate. In other words, the cat’s body is abnormally working at full speed as if it was running a marathon, despite the cat being practically full time sitting on the sofa.
The thyroid enlarges during the course of the disease and this is most often caused by benign tumors of the gland. It is still not known exactly what makes these tumors appear.
Signs and symptoms
Since the metabolism is strongly accelerated by the increased hormones, the whole body needs to adapt to meet the new metabolic demands. This means that different organs can be affected and therefore various signs and symptoms can occur, including:
- weight loss despite increased appetite
- anxiety (with or without vocalizing) to aggressiveness
- increased water intake and urine production
- recurrent vomiting or diarrhea
- unkempt or greasy fur
Heart rate and pumping pressure usually rise, which may lead to hypertension (high blood pressure) and heart disease. Cats with hyperthyroidism can also show sudden blindness due to retinal bleeding or detachment as a repercussion from hypertension.
Does your cat have any of these symptoms? If the answer is yes, do not hesitate to bring it to our Tierarztpraxis Bärenwiese team for a health evaluation!
Diagnosis
The diagnosis of hyperthyroidism in cats is usually quite straightforward. The vet will suspect the disease mainly if they palpate the neck region and notice the enlarged gland. To confirm the suspicion, it is necessary to obtain a blood sample and measure the total T4 level, which is the main hormone produced by the thyroid. An elevated result means that the animal has hyperthyroidism. However, some cats have symptoms, a physical examination compatible with the illness and a normal
level of TT4. In this case, more specific tests are needed.
It is recommended that every hyperthyroid cat has a complete blood work, urinalysis, blood pressure and cardiological evaluation
Treatment
There are four ways to treat hyperthyroidism in cats: oral medication, radioactive iodine therapy, surgery or prescription diet. The best treatment option depends on many factors and consequently, only the veterinarian can decide it after careful evaluation.
Oral Medication
Anti-thyroid drugs act by blocking the overproduction of thyroid hormones. They are usually given twice a day lifelong and are relatively inexpensive, leading to good control of the disease. Symptom improvement usually starts around three weeks after the first dose. Frequent TT4 blood level measures may be necessary in the beginning of the treatment so that your vet finds out the exact amount of medication your cat needs. Side effects observed include vomiting, loss of appetite, anemia, tiredness, and bleeding.
Radioactive Iodine Therapy
Radioactive iodine (I-131) is a substance that circulates through the blood and destroys only the sick cells of the thyroid gland. The healthy cells of the thyroid and the parathyroid glands are not affected. As the I-131 is easily applied subcutaneously (under the skin) just like a vaccination, no anesthesia is required.
This treatment leads to a cure of about 95% of the affected cats within 3 months and has no serious side effects. However, because it is a radioactive substance, only specific centers are allowed to offer this therapy. In addition, the patient who receives I-131 needs to remain hospitalized until the levels of radioactivity in its blood decrease to safe values, which takes an average of three days up to a week. The hospitalization is necessary to avoid risks to its owners, to other animals living
in the same house and to the environment.
Surgery
The surgery to remove the thyroid, or thyroidectomy, can also be curative and eliminates the need for medication. However, it requires general anesthesia and therefore has inherent risks, both referring to the procedure itself (unintentional lesion of the parathyroid, blood vessels and nerves) and the general health of the animal (if it has other concomitant diseases or lesions in other organs).
There are still other factors to consider when planning the surgery, such as specific imaging tests (e.g. nuclear scans) to evaluate whether only one or both sides of the gland are affected, if there is production of glandular tissue in other parts of the body, etc. Only with these detailed data, your veterinarian will be able to estimate if the animal will need one or more surgeries, the real advantages of performing it and the expected results.
The cat will need medication for about one month prior to the surgery to determine if it has a secondary medical condition that was masked by the hyperthyroidism before, and to evaluate its clinical response to the medication. Cats that successfully undergo the initial treatment without complication will be eligible for surgery. After the procedure, the cat may be hospitalized for two days. TT4 level will be measured within one or two weeks post surgery.
Prescription diet
The treatment with a diet containing a limited amount of iodine is still controversial and more research is needed to prove its effectiveness. The advantages of a prescription diet include low costs and ease of treatment as long as the cat accepts the new food. Nevertheless, as the cat may already have more than one disease, it is also possible that the veterinarian prefers to keep its old diet to prevent a worsening of preexisting health conditions.
Prognosis
With the appropriate therapy, prognosis is usually good if there are no complications affecting other organs.
At Tierarztpraxis Bärenwiese you will definitely find good options to diagnose and treat your pet. Not only do we handle your animal with love and respect, but also work according to the parameters set by the Official European Veterinary Entities.
Do you need more help? Contact us and schedule an appointment!
