Older dogs usually do not have the same energy level as when they were puppies, which should come as no surprise. However, not all of this “slowing down” may be due to age alone; there are a number of health conditions that may contribute to this, and treatment of these conditions may provide some renewed vigor. One of the most common treatable diseases that slows down older dogs is hypothyroidism.

Hypothyroidism is caused by either an inflammatory or degenerative change within the thyroid gland. These changes can occur at any age, although most dogs are “middle-aged” to older when the process starts. Both the inflammatory and degenerative causes produce the same result — low levels of thyroid hormone circulating in the bloodstream. While there may be a genetic component to hypothyroidism, it cannot be predicted which dogs will develop the condition.

The thyroid gland controls the overall level of metabolism in the body. As such, imbalances in the level of thyroid hormone can affect many different body systems, such as the hair coat, musculoskeletal system, cardiovascular system, and central nervous system.

One of the more common symptoms of hypothyroidism is the general “slowing down” as previously mentioned. As the metabolism slows, energy levels drop and the dog becomes less active or may become easily fatigued. The combination of a decreased metabolism and decreased ability to exercise leads to weight gain, which in some cases may be quite significant.

This weight gain does not usually coincide with an increased appetite — in fact, it is usually the opposite, as the lower metabolism may lead to decreased appetite.

Adding to the decreased energy levels and mobility is the fact that low thyroid levels in rare cases may result in decreased nerve function. Affected dogs may have generalized neurological weakness or wobbliness, and may even have a decrease in their reflex responses. The effect on nerves in the brain may cause an overall dullness.

Another common manifestation in hypothyroid dogs is skin and hair coat issues. Many dogs with low thyroid will have a sparse hair coat, even to the point of baldness in areas. The hair itself becomes dry and brittle. These changes, as a primary condition, are not associated with rashes or itchiness; the low hormone level acts without inflaming the skin.

However, hypothyroidism additionally predisposes dogs to secondary skin infections with bacteria and yeast, which does result in itchy skin.

A veterinarian may have a high level of suspicion that a dog has low thyroid hormone levels based on the history provided by the owner and a thorough physical exam. In most cases, the initial screening test for hypothyroidism is a measure of the total thyroid hormone level circulating in the blood.

A condition called “euthyroid sick syndrome” can make an animal have low circulating total thyroid hormone levels due to illness rather than due to a truly underproductive thyroid gland. For this reason, there are other tests than can be run in conjunction with or as a follow-up to the initial screening test to better define the problem.

To definitively diagnose a dog with hypothyroidism, a veterinarian must consider the big picture: symptoms, physical examination findings, and blood tests. If any one supports a low thyroid but not the others, the dog may not need treatment.

Medication for hypothyroidism is given orally and is generally well-tolerated. There are no significant side effects expected if dosed appropriately—the medication just replaces the hormone that has been lost. The medicine is given lifelong, but may need to be increased periodically if the disease progresses. Treatment will often reverse many of the symptoms of hypothyroidism; most dogs will have improved skin and hair, lose weight, and have more energy than before they were treated. Older dogs may not act quite so old if this condition is managed appropriately.

Dog owners who may be concerned that their dog is hypothyroid should schedule an exam with a veterinarian to discuss to evaluate for this condition and its effects.

— Keith Rode is a veterinarian at Woodland Veterinary Hospital and a graduate of UC Davis. For more information, call (530) 666-2461.

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