We ran routine blood work which was all completely normal. However, a screening serum total T4 concentration was low at 0.4 μg/dl (reference range, 0.38-4.0 μg/dl). I added on a free T4 concentration and that was also low at 0.3 ng/ml (0.6 to 3.7 ng/ml).
Would you recommend starting a thyroid supplementation in this dog?
I doubt if this dog is truely hypothyroid for a number of reasons (1-3).
- First of all, the clinical signs the dog is showing are not at all characteristic of hypothyroidism.
- Secondly, the dog has neither anemia or hypercholesterolemia, which would make a diagnosis of hypothyroidism more likely.
- Finally, would be very unusual for a 17-year old dog to develop hypothyroidism; most dogs with hypothyroidism are young to middle age adult dogs, not geriatric animals.
- Sulfur antibiotics
- Clomipramine (Clomicalm)
- Aspirin and other anti-inflammatory drugs
Of course, if you do believe that the dog has hypothyroidism, then the next step would be to verify the low serum T4 concentration, repeat the serum free T4 using an equilibrium dialysis technique if possible, and to measure a serum cTSH concentration (2,3). If the total and free T4 remain low and the cTSH value is high, then treatment would be indicated.
The most accurate way to make a diagnosis (or rule out) a diagnosis of hypothyroidism is by use of thyroid scintigraphy (6,7). Although not widely used or available as a diagnostic test for dogs with suspected hypothyroidism, the diagnosis of hypothyroidism is easily made by the lack of finding any visible cervial thyroid tissue with thyroid imaging (see Figure below).
, there was no overlap between dogs with primary hypothyroidism and dogs with nonthyroidal illness when thyroid scintigraphy was employed (6). Of all of the current thyroid imaging techniques (CT, ultrasound), nuclear imaging is considered to be the best test for dogs with suspected hypothyroidism.
- Chastain CB. Canine pseudohypothyroidism and covert hypothyroidism. Problems in Veterinary Medicine 1990;2:693-716.
- Mooney, CT. Canine hypothyroidism: A review of aetiology and diagnosis. New Zealand Veterinary Journal 2011;59:105-114.
- Peterson ME, Melián C, Nichols R. Measurement of serum total thyroxine, triiodothyronine, free thyroxine, and thyrotropin concentrations for diagnosis of hypothyroidism in dogs. Journal of the American Veterinary Medical Association 1997;211:1396-1402.
- Kantrowitz LB, Peterson ME, Trepanier LA, et al. Serum total thyroxine, total triiodothyronine, free thyroxine, and thyrotropin concentrations in epileptic dogs treated with anticonvulsants. Journal of the American Veterinary Medical Association 1999;214:1804-1808.
- Williamson NL, Frank LA, Hnilica KA. Effects of short-term trimethoprim-sulfamethoxazole administration on thyroid function in dogs. Journal of the American Veterinary Medical Association 2002;221:802-806.
- Diaz Espineira MM, Mol JA, Peeters ME, et al. Assessment of thyroid function in dogs with low plasma thyroxine concentration. J Vet Intern Med 2007;21:25-32. http://www.ncbi.nlm.nih.gov/pubmed/17338146
- Taeymans O, Peremans K, Saunders JH. Thyroid imaging in the dog: current status and future directions.J Vet Intern Med 2007;21:673-684. http://www.ncbi.nlm.nih.gov/pubmed/17708386