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One of the diagnostic methods for an underactive thyroid in cats involves a blood test.
15 May 2023 | The thyroid gland plays a significant role in your cat’s body. But what happens when this organ is impaired and produces too few thyroid hormones? This article provides key information about hypothyroidism in cats and shows how you can help your furry friend.
Hypothyroidism occurs when the thyroid gland produces too few thyroid hormones. These hormones typically influence a variety of mechanisms such as energy metabolism or heart activity.
Due to the importance of thyroid hormones for vital bodily functions, untreated hypothyroidism can lead to dangerous damage within a cat’s body.
The thyroid is a large gland that forms the thyroid hormones triiodothyronine (T3) and thyroxine (T4) and releases them into the bloodstream.
The thyroid is stimulated by hormones sent from the brain. These include the stimulating hormone TSH (thyroid-stimulating hormone) and the inhibiting hormone TRH (TSH-releasing hormone).
Cats are rarely affected by hypothyroidism compared to dogs. However, it is common for many domestic cats to develop [hyperthyroidism (an overactive thyroid)], especially in older age.
The inherited form of hypothyroidism is said to occur more frequently in Abyssinian cats – although it is still rare. This condition is presumably autosomally recessively inherited in this breed, meaning the disease only manifests if both parents carry a defective gene related to the trait.
The symptoms resulting from hypothyroidism in cats depend on the specific cause.
If a cat suffers from hypothyroidism due to genetic factors, symptoms will appear early on. Affected kittens show the following symptoms:
In cats with this form, thyroid disturbances often only become apparent following a blood test. The serum T4 levels are low, while TSH levels are within the reference range or elevated.
Cats with this form are noticeable because they appear lethargic and their fur thins. The skin is increasingly affected, manifesting as seborrhea, a non-contagious skin inflammation. In addition, these animals might lose their appetite.
If your cat appears altered in behaviour or appearance, you should consult your vet promptly to counteract any illness in good time.
If you suspect your cat is suffering from hypothyroidism, the vet can confirm this with various tests. However, it may take some time to receive a reliable diagnosis since various factors can complicate findings.
Expect to find lower concentrations of thyroid hormones in the blood with hypothyroidism:
| Form | TSH | T3 | Free T3 | T4 | Free T4 |
| Primary | elevated | lowered | lowered | lowered | lowered |
| Secondary | lowered | lowered | lowered | lowered | lowered |
Note: “Free” thyroid hormones refer to the unbound fraction of thyroid hormones that are not attached to plasma proteins.
Several factors complicate the diagnosis of hypothyroidism in cats:
Your vet can identify congenital thyroid damage using imaging techniques such as X-rays or a scintigraphy.
Hypothyroidism in cats can arise from various causes, leading to classification into two forms:
Iatrogenic means caused by medical treatment. This is the most common form of the disease in cats, which can result from treatments for hyperthyroidism, such as:
The congenital disease form involves inherited defects that impair hormone production in the thyroid gland.
Inflammation of the thyroid gland can lead to spontaneously occurring hypothyroidism. However, there are very few reports of this in cats.
If your cat produces too few thyroid hormones, they need to be supplemented with medication. The recommended dosage is ten to twenty micrograms of T4 per kilogram of body weight per day.
The medication often shows effects after just a few weeks. However, to ensure the hormones have stabilised, your vet should recheck the levels approximately four to six weeks after the first dose.
If the T4 value is still outside the reference range, the dose must be adjusted gradually in consultation with your vet.
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The prognosis for hypothyroidism in cats depends on the underlying cause. While the secondary, acquired form generally has a good prognosis with early treatment, the prognosis for the congenital form is more guarded.
Due to the complex development of hypothyroidism, it is hardly possible to prevent it in cats. Fortunately, most cats have a low tendency to develop the disease.
Nevertheless, it’s beneficial to keep and feed your cat in a species-appropriate manner. Regular health check-ups at the vet can also help in early detection and effective treatment of illnesses.
This article from zooplus Magazine is purely informative. If your pet is experiencing discomfort, contact your veterinarian for diagnosis and treatment.
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At the Justus-Liebig-University of Giessen I was extensively trained as a veterinarian and was able to gain experience in various fields such as small animal, large animal and exotic animal medicine as well as pharmacology, pathology and food hygiene. Since then, I have been working not only as a veterinary author, but also on my scientifically driven dissertation. My goal is to better protect animals from pathogenic bacterial organisms in the future. Besides my veterinary knowledge, I also share my own experiences as a happy dog owner and can thus understand and enlighten fears and problems as well as other important questions about animal health.
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