Hypothyroidism in Pets and Companion Animals

Hypothyroidism is caused by a lack of production of the metabolism-regulating hormone thyroxine by the animal’s thyroid gland. The thyroid gland is located in a dog or cat’s neck, and is responsible for producing many of the hormones used in various chemical processes in the body, including the regulation of metabolism and other cellular processes.

The thyroid’s output is usually dictated by signals from the “master gland,” the pituitary. But despite the signals received from the pituitary, the thyroid, in an affected animal, still cannot produce the desired amount of the hormone.

Hypothyroidism in Pets

Hypothyroidism in cats is very uncommon and usually transitory in nature. Common causes in cats include surgery or radioiodine treatment for hyperthyroidism (much more common in cats).

In dogs, however, hypothyroidism is very common, though generally not life-threatening. Common causes for the condition in dogs include their immune system attacking their thyroid, shrinking of the thyroid as the animal ages, or the presence of a tumor on the thyroid.

Hypothyroidism is more common in middle-aged and older dogs, and certain breeds that include boxers, Doberman pinschers, golden retrievers, cocker spaniels, and dachshunds.

Signs and Effects of Hypothyroidism in Pets

Cats are rarely affected by hypothyroidism. When they are, the symptoms include weight gain, lethargy, muscle weakness, inactivity, constipation, mental dullness, matted hair, loss of hair, unkempt appearance, low body temperature, and a delay in the coming in of teeth.

In dogs, the first sign of hypothyroidism is hair loss, typically first seen on the trunk of the animal, their tail, and the backs of the rear legs. Other signs include flaky skin without redness or itchiness, sluggishness, a thinning and dulling of the coat, weight gain, intolerance to cold, a slowing of the heart rate, muscle loss, and a propensity for contracting ear and toenail infections.

Diagnosis and Treatment of Hypothyroidism in Pets

With cats, a medical history and complete physical with blood work will generally be enough to identify the condition. However, finding the underlying cause of hypothyroidism may require considerably more testing. But again, with cats, the condition is usually temporary and may require little treatment other than an adjustment in medication, or waiting for the condition to go away on its own.

With dogs, a blood test to determine a deficiency in thyroxine, followed by tests to determine what is causing the condition, will typically lead to a diagnosis and treatment plan. Hypothyrodism is not life threatening in dogs, but will seriously compromise a dog’s quality of life, so it should not go without treatment.

Thankfully, most cases of hypothyroid in dogs are simple and relatively inexpensive to treat. An oral drug such as Levothyroxine (a synthetic hormone), taken for the remainder of the animal’s life will typically address the condition. However, getting the dose dialed in may take some time. It should be mentioned that overmedicating for hypothyroidism in dogs is a leading cause of hyperthyroidism.


Author: Giano Panzarella