Signs of hypothyroidism in cats and treatment options

Hypothyroidism, or abnormally low levels of thyroid hormone, is a rare condition in cats that most often occurs secondarily to treatment for feline hyperthyroidism. The thyroid gland controls a cat’s metabolic rate, and clinical signs can be widespread and vary in severity. If you have a cat, read on to learn:

• What happens in cats with hypothyroidism
• Symptoms of hypothyroidism in cats
• How feline hypothyroidism is diagnosed and treated

Cats with hypothyroidism can often live normal lives if their condition is well managed through thyroid hormone supplementation or an adjustment to hyperthyroidism treatment. Mildly affected cats may show no symptoms, but others may show weight gain, lethargy, loss of appetite, and changes to their skin and fur.

Hypothyroidism in cats is an endocrine condition characterized by abnormally low levels of thyroid hormones. The hormones created by the thyroid gland are responsible for metabolism and affect multiple body systems. Hypothyroidism is thought to be rare in cats but may be underdiagnosed in cats being treated for hyperthyroidism. Pet owners need to be aware of the disease since even cats with mild forms or cats not showing obvious symptoms may benefit from treatment.

How cats get hypothyroidism

Most cases of hypothyroidism in cats occur as a result of treatment for feline hyperthyroidism, a condition in which thyroid hormone levels are abnormally high. Treatment for hyperthyroidism may unintentionally drive hormone levels too low, resulting in iatrogenic hypothyroidism.

Feline hypothyroidism can also develop as a result of brain injury, tumors, or the autoimmune destruction of the thyroid gland. Naturally occurring hypothyroidism in cats is very rare, but it is possible for kittens to be born with congenital hypothyroidism, also known as cretinism. Cretinism may be underdiagnosed, as many affected kittens appear normal but often die young before symptoms become apparent.

Symptoms of hypothyroidism vary between cats and can include:

• Lethargy or mental dullness
• Unexplained weight gain
• Loss of appetite
• Aversion to cold or seeking warm places
• Hair loss
• Poor hair coat
• Thickened skin
• Dry, flaky skin
• Decreased heart rate and body temperature

Symptoms of hypothyroidism can be easily overlooked and mistakenly attributed to normal cat behavior, such as:

• Seeking warm, comfortable places to rest
• Weight gain from free feeding or not measuring food
• Cat “laziness”

Kittens with cretinism may develop dwarfism, with signs such as very short limbs, overly round heads, and short bodies.

After a physical exam, a veterinarian will likely recommend diagnostic testing. Hypothyroidism symptoms can be mild, and other medical conditions have similar clinical signs, so testing is necessary for an accurate diagnosis. Diagnostic tests may include:

• Routine blood work
• Diagnostic imaging, such as X-rays and ultrasounds
• Urinalysis

Additional tests may be recommended to rule out other, more common diseases. If hypothyroidism is suspected, a specialized blood test is used to measure changes in thyroid hormone levels in response to an injection that stimulates their production. If the thyroid levels remain low after stimulation, an accurate diagnosis of hypothyroidism can be made.

Treatment for feline hypothyroidism involves getting thyroid levels back up to normal levels. Follow-up blood tests are often recommended to monitor thyroid levels and determine the right dosage of medication. “If iatrogenic hypothyroidism develops during treatment for hyperthyroidism, the outcome depends on how the hyperthyroidism was being treated,” explains Dr. Jo Myers, a veterinarian on the Vetster platform. “If methimazole is being given, the dose may be lowered or discontinued altogether. If hyperthyroidism was treated with surgery or radioactive iodine therapy, thyroid tissue has been permanently removed or destroyed. This is not reversible, and supplemental medication must be given as treatment for hypothyroidism.” The prognosis of hypothyroidism in cats is generally good, especially if it is caught early and managed well.

Can hypothyroidism in cats be cured?

It is possible for some cats to develop temporary iatrogenic hypothyroidism following radioactive iodine therapy for hyperthyroidism. Normal levels may also return in a cat who develops low thyroid hormone levels while on methimazole once the dose is adjusted. In some cases, however, the loss of thyroid hormone production is permanent and the cat remains hypothyroid for the rest of its life. Hypothyroidism can usually be well managed with treatment and monitoring by a veterinarian. With good management, symptoms usually resolve, and affected cats can live normal lives.

The symptoms of hypothyroidism occur more commonly with other disorders. If your cat is not being treated for hyperthyroidism and develops symptoms such as lethargy, appetite loss, or unexplained weight gain, another condition is likely to blame. When treating feline hyperthyroidism, keep a close watch on any changing symptoms and report changes to a vet. Regular blood work is recommended to catch asymptomatic hypothyroidism, which can be detected and successfully treated.

Always talk to a veterinarian when your cat shows changes in their behavioral or physical health, even if they seem minor. In addition, talk to a vet if your kitten is not growing at the proper rate or appears to have physical deformities. If you have questions about your feline friend’s symptoms or treatment of hyperthyroidism in cats, an online vet is available to answer them on the Vetster platform.

What are the symptoms of hypothyroidism in cats?

Symptoms of hypothyroidism in cats usually occur during treatment for hyperthyroidism and include lethargy, weight gain, loss of appetite, and changes to the skin and hair. Clinical signs can vary and be easily mistaken for normal cat behavior. Some cats with mild hypothyroidism may have no obvious signs at all.

What is the life expectancy of a cat with hypothyroidism?

The prognosis and life expectancy of cats with hypothyroidism varies depending on the underlying cause. Most cases of feline hypothyroidism are a result of treating hyperthyroidism. Hypothyroidism can often be well managed with medication, and cats can live normal lives.

What happens if hypothyroidism in cats is left untreated?

Hypothyroidism results in a lowered metabolic rate that can severely affect multiple organs, depending on the severity of the condition. Some cats with mild hypothyroidism have few to no symptoms, while for others it can be deadly if left untreated.