Thyroid -- W Jean Dodds, DVM

On Saturday, March 1, I attended a seminar hosted by the Croix Valley Tracking Club. Dr. Dodds filled a whole day with fascinating information about canine health issues. Since she is most well known for her research in the area of thyroid dysfunction, that's where I'll start.

Basal thyroid levels are different for puppies (higher), middle aged dogs, and geriatrics (lower). More importantly, basal thyroid levels are also dependent on breed and even different lines within a breed (her example was the difference in basal thyroid levels for African bred Basenjis and North American bred Basenjis). Sighthounds have their own category, and their basal thyroid level is lower. For this reason, it is important to assess thyroid function with the signalment (age, breed, sex) of each dog in mind. She is obviously a proponent of sending all thryoid samples to her for analysis and diagnostics at her facility: Hemopet.

Why is her report different?
First, the analysis is more comprehensive. The Thyroid Profile 5 includes T4, freeT4, T3, freeT3, and TgAA. (Many veterinarians are still recommending just a T4 for screening purposes, which provides incomplete data for accurate diagnosis.) She is an OFA certified laboratory as well as offering her own Thyroid Gold registration and certificate for dogs deemed normal within their respective breed's levels.

Second, the results are interpreted by Dr. Dodds personally and a consultation with follow up is included in the price.

Third, each dog's result is evaluated based on the data collected for other dogs of the same breed. Dr. Dodds confidently says this is the most accurate way of correctly diagnosing (and treating) hypothyroidism in dogs. She does offer the option of interpreting thyroid results from an outside lab, as that is more convenient for some people. However, she did mention during a break that there are also differences in medical testing equipment and reference ranges for humans and animals. Therefore, she will recommend sending the sample to certain labs over others.

Why test?
Symptomatic dogs are generally the only dogs tested. The problem is that there are "normal" symptoms that most vets, and even the general public will notice. And then there are the not-so normal symptoms. Typical clinical signs include: moodiness, erratic temperament, disorientation, hypoattentiveness, depression, anxiety, unprovoked aggression, sudden onset seizure disorder, and compulsiveness. More subtle changes include a change in muscle in the face which leads to a change in the dog's expression; there can be significant temporal muscle wasting above and below the eyes. Seborrhea oleosa (oily skin) and seborrhea sicca (dry skin) can both be indicators of hypothyroidism. Inability to regulate body temperature is also a symptom of hypothyroidism that can go unnoticed for months due to weather changes, among other reasons.

Breeding is the number one reason a dog should be tested for hypothyroidism. Autoimmune thyroiditis is a heritable trait and will be present in the dog, even if not showing clinical signs. If a dog has autoimmune thyroiditis (genotype), that doesn't automatically mean the dog is currently hypothyroid (phenotype). Testing for heritable autoimmune thyroiditis requires T3AA, T4AA, and TgAA. Dr. Dodds recommends that potential breeding dogs be screened for the first time just after puberty. In bitches that is 12-16 weeks from the onset of estrus, and in males 10-14 months. Ideally, the dog would have two negative tests by age 3 before considering breeding. It is important to continue to screen regularly (recommended yearly for breeding dogs, less frequently for non-breeding dogs).

Other causes
Basal thyroid level can be suppressed up to 25% by certain medications such as steroids, phenobarbital, sulfonamides (overlooked sulfas: Zonisamide & Deramaxx), and excess iodine. Iodine (found in kelp, a commonly used dietary supplement for dogs) excess and deficiency can cause immune responses. Iodine depletion is one cause of dietary induced hypothyroidism. While Dr. Dodds is a proponent of raw feeding, she did caution feeding throat/gullet meat because it has been linked to dietary hypothyroidism in dogs and hyperthyroidism in cats. Her advice was to know where the meat is coming from, specifically. Rabies vaccines given within 45 days will cause an elevated TgAA. Neck pressure from all types of collars has also been linked to thyroid disorders. An article by Peter Dobias, DVM was referenced as an anecdotal example of neck injuries leading to hypothyroidism.

Dogs and cats should receive thyroid treatment twice daily. In an ideal world the medication would be given one hour before ingestion of calcium or soy and exactly twelve hours apart. Realistically, it is more important to give the medication one hour before or three hours after meal time. The animal should either be pilled dry, or you can use a food without calcium or soy such as peanut butter. Read the label carefully on anything that is designed to "hide" the medication, to make sure calcium and soy aren't ingredients. Brand name (Soloxine, ThyroTabs) thyroid treatment has proven to provide more reliable results than generic. Depending on the type of thyroid disorder, natural thyroid supplementation can be considered. These are typically bovine or porcine based (Nature Throid, Westhroid Pure Thyroid, ERFA-Canada only). Supplementation should not be started before consulting with a veterinarian.