News Dr. Peterson was recently quoted in an article published in Veterinary Practice News about the increasing rate of pet obesity in our country: AP
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CE and the City is coming soon (only 1 month from now) and Dr. Peterson will again be lecturing (his topic this year is an update on diagnosing feline hyperthyroidism, a talk based in large part on his recent research findings).
Talks this year will be one hour long and there will be three lectures running simultaneously. To register for CE and the City, click here. Admission is a $25 donation to NY SAVE. This is a great way to get up to 8 hours of CE locally. |
Association of Veterinary Doctors of Quebec
Montreal, Quebec, Canada, April 19 - 21, 2013
Topics:
• Feline Hyperthyroid Update: Some Things Old But Everything New
• Insulin Choices for the Diabetic: Which Preparations Work Best?
• Management of the Problem Diabetic: Acromegaly, Cushing’s and Other Causes of Insulin Resistance
• Diagnostic Testing for Canine Hyperadrenocorticism —Confusion or Clarity?
• What's the Best Treatment for Cushing's Disease? Trilostane vs. Mitotane
• Typical, Atypical, and Secondary Addison's Disease: How Do We Diagnose and Treat These Three Subtypes?
CE and the City
New York, New York, May 4, 2013
Topics:
• Diagnostic Testing for Thyroid Disease in Cats: More Than Just T4
Capital District Veterinary Medical Society (CDVMS)
Albany, New York, May 8, 2013
Topics:
• Insulin Choices for the Diabetic: Which Preparations Work Best?
• What's the Best Treatment for Cushing's Disease? |
Palpating the thyroid gland: a key part of diagnostic testing for cats with hyperthyroidism |
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Patient History and Examination
Ruby, a 9-year-old, female DSH weighing 5.1 kg was referred to the Animal Endocrine Clinic for evaluation of hyperthyroidism and possible radioiodine treatment.
The cat was initially presented to the referring veterinarian for her yearly examination. Mild weight loss (0.5 kg) was noted on examination. On questioning, the owner revealed that Ruby had a great appetite but no coughing, sneezing, vomiting, diarrhea, or polyuria had been observed.
Routine blood tests (CBC, serum chemistry panel, urinalysis) were all within reference range limits. Results of a serum T4 determination revealed a high-normal total T4 value (2.8 µg/dl; normal, 1.0-4.0 µg/dl). To help exclude hyperthyroidism as the cause of the weight loss, a free T4 concentration was "added on" to Ruby's thyroid testing panel. Results showed a slightly high free T4 value (57 pmol/L; normal, 10-50 pol/L). Based on the high free T4 results, hyperthyroidism was diagnosed and the cat referred for radioidodine treatment.
On my examination, the cat was bright, alert, and active. The cat's body condition score and muscle condition score were both normal. The heart rate was 180 bpm, and abdominal palpation revealed no abnormalities. Cervical palpation (see photo above), however, revealed mild enlargement of both thyroid lobes (i.e., a tiny, bilateral goiter). |
Thyroid Scintigraphy
In order to confirm the diagnosis of mild hyperthyroidism and better stage the disease in Ruby, a thyroid scan was performed (see Thyroid scan, below). The two thyroid lobes were of normal shape and were symmetrical in size. The thyroid lobes were within the high-normal limits for size, with each thyroid lobe measuring 1.5 by 0.9 cm. The thyroid uptake of the radionuclide was also normal, as demonstrated by the normal thyroid:salivary ratio (1.0; normal <1.3). Based on these thyroid scan measurements, Ruby was not hyperthyroid. |
Thyroid scintigraphy. Notice that both thyroid lobes are symmetric in size and position. The thyroid uptake ("brightness") of the 2 thyroid lobes is similar to the salivary glands. |
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Complete thyroid panel
Because of the normal thyroid scan findings, a complete thyroid panel, including a total T4, T3, free T4, and TSH) was performed. Results showed normal values for total T4 (2.5 µg/dl; normal, 0.8-4.0 µg/dl), T3 (45 ng/dl; normal, 40-150 ng/dl), free T4 (40 pmol/L; normal, 10-50 pmol/L) and TSH (0.04 ng/ml; normal, 0-0.30 ng/ml).
Again, because all of these results were within normal range limits, Ruby was not considered to be hyperthyroid.
Discussion
With the normal serum concentrations of T4, T3, free T4, and TSH, as well as the normal uptake of the radioisotope on the thyroid scan, I do not believe that Ruby is hyperthyroid. I could palpate a tiny bilateral goiter, but that can be a normal finding in some euthyroid cats (1-4). In any case, both thyroid lobes were completely normal on thyroid imaging.
Thyroid scintigraphy helps confirm the diagnosis of hyperthyroidism, which is very useful in cats in which a thyroid nodule cannot be palpated or when only a very small goiter is palpated (5,6). Because thyroid scintigraphy directly visualizes functional thyroid tissue and the “uptake” of the radioisotope can be estimated by determining the thyroid:salivary ratio, thyroid imaging can diagnose hyperthyroidism even before laboratory tests are consistently abnormal. Thyroid scintigraphy is considered the gold standard for diagnosing mild hyperthyroidism in cats.
Thyroid scintigraphy can also exclude the diagnosis of hyperthyroidism in euthyroid cats that have false-positive elevations in their serum T4 or free T4 values (5-7). Studies of cats with nonthyroidal illness (e.g., diabetes, renal, gastrointestinal, or liver disease) have shown that between 6-12% of these cats have falsely high serum free T4 values, despite the fact that they are not hyperthyroid. In addition, routine screening of an apparently healthy senior cat occasionally reveals laboratory abnormalities that include slightly high total or free T4 concentrations, consistent with mild hyperthyroidism. As with sick cats with falsely high free T4 values, however, a thyroid nodule cannot be palpated in most of these cats, and thyroid imaging may fail to confirm hyperthyroidism (5-7).
In my experience, about 30% of cats presenting with a mid- to high-normal total T4 value, together with a high free T4 concentration, will turn out to be euthyroid based on results of thyroid scintigraphy. Therefore, many cats diagnosed on the basis of a high free T4 value alone turn out NOT to be hyperthyroid, and instituting any treatment for hyperthyroidism would be contraindicated in these euthyroid cats.
The accurate diagnosis of hyperthyroid depends on much more than just looking and T4 and free T4 levels. For more information on this topic, try to attend my upcoming talk at CE and the City, when I'll be discussing this issue in much more detail.
References
1. Ferguson D, Freeman R. Goiter in apparently euthyroid cats In: August JR, ed. Consultations in Feline Internal Medicine. St. Louis: Elsevier Saunders, 2006.
2. Norsworthy GD, Adams VJ, McElhaney MR, et al. Palpable thyroid and parathyroid nodules in asymptomatic cats. J Feline Med Surg 2002;4:145-151.
3. Norsworthy GD, Adams VJ, McElhaney MR, et al. Relationship between semi-quantitative thyroid palpation and total thyroxine concentration in cats with and without hyperthyroidism. J Feline Med Surg 2002;4:139-143.
4. Boretti FS, Sieber-Ruckstuhl NS, Gerber B, et al. Thyroid enlargement and its relationship to clinicopathological parameters and T4 status in suspected hyperthyroid cats. J Feline Med Surg 2009;11:286-292.
5. Broome MR. Thyroid scintigraphy in hyperthyroidism. Clin Tech Small Anim Pract 2006;21:10-16.
6. Peterson ME. Hyperthyroidism in cats In: Rand JS, Behrend E, Gunn-Moore D, et al., eds. Clinical Endocrinology of Companion Animals. Ames, Iowa Wiley-Blackwell, 2013;295-310.
7. Peterson ME. Diagnostic testing for hyperthyroidism in cats: more than just T4. Journal of Feline Medicine and Surgery 2013:submitted for publication. |
Peterson ME. Nutritional management of endocrine diseases in cats. Canadian Vet 2013;8(2):20.
Peterson ME: Hyperthyroidism, In: Greco D, Davidson A(eds), Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Endocrinology and Reproduction. Ames, Iowa, Wiley-Blackwell. 2013 (in press).
Bargellini P, Orlandi R, Paloni C, Rubini G, Fonti P, Peterson ME, Boiti C. Contrast-enhanced ultrasonographic characteristics of adrenal glands in dogs with pituitary-dependent hyperadrenocorticism. Veterinary Radiology & Ultrasound 2013.
Peterson ME. Diagnostic testing for hyperthyroidism in cats: more than just T4. Journal of Feline Medicine and Surgery 2103; submitted. |
Gene Therapy: A Cure for Canine Diabetes
The dogs in the study, once treated, experienced long-term normoglycemia, both in the fasting or fed state, with no need for exogenous insulin therapy.
Managing Dogs with Insulin-Sensitive, Brittle Diabetes
My problem patient is a 13-year-old, female-spayed Yorkie with brittle diabetes mellitus. In contrast to many diabetic dogs that I see, this dog is very insulin sensitive, with frequent bouts of hypoglycemia.
How Radioiodine Works to Cure Cats with Hyperthyroidism
Thyroid hormones are the only iodinated organic compounds in the body. Ingested stable iodine (127-I) in the diet is converted to iodide in the gastrointestinal tract and absorbed into the circulation.
Treating Hyperthyroid Cats with Radioiodine: The Pros and Cons
Hyperthyroidism is the most common endocrine disorder in cats, most frequently associated with adenomatous hyperplasia (or adenoma) involving one or both thyroid lobes.
Hyperthyroidism in Cats: Past and Upcoming Topics
For my next series of posts, I'm getting back to this series to discuss the next treatment option — namely, radioactive iodine (radioiodine; I-131)
Journal of Feline Medicine and Surgery Appoints Dr. Mark Peterson to Editorial Board
Dr. Mark E. Peterson was recently appointed to the Editorial Board of the Journal of Feline Medicine and Surgery (JFMS).
Obesity Epidemic Expanding in Dogs and Cats
The rates of overweight and obesity in dogs and cats in the U.S. continued to increase in 2012, with the number of overweight cats reaching an all-time high.
Using a Glucagon Emergency Kit for Insulin-Induced Hypoglycemia
Metabolic and Hormonal Responses to Subcutaneous Glucagon in Healthy Beagles |
The Animal Endocrine Clinic is the only clinic of its kind in the country that specializes in the diagnosis and treatment of cats and dogs with endocrine disorders. Dr. Peterson has set up two NY clinics (Manhattan and Bedford Hills) to service clients from New York City, Long Island, Westchester County, New Jersey and Connecticut.
This Clinic is separated into three divisions: the Endocrine Clinic, dedicated to diagnosing and treating dogs and cats with endocrine disorders; the Hypurrcat treatment center designed for treating hyperthyroid cats with radioactive iodine (I-131); and Nuclear Imaging for Animals, a state-of-the-art medical imaging facility where we use radioactive tracers to perform nuclear scanning (scintigraphy) for diagnosing of thyroid, bone, liver, and kidney diseases in dogs and cats.
The Animal Endocrine Clinic is a referral-only hospital, and does not offer prophylactic or routine care. We can be reached by phone at (212) 362-2650 or (914) 864-1631; by email at info@animalendocrine.com or on the web at www.animalendocrine.com. |
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