Lecture 9 Rosenthal

Hypothyroidism in a Red-lored Amazon

Presenting Author: Karen L. Rosenthal, DVM, MS, Dipl ABVP (Avian), and Matthew Johnson, VMD

Department of Clinical Studies, Philadelphia, University of Pennsylvania

Interpretive Review and comments by Dr. Nemetz:

Dr. Nemetz and Dr. Rosenthal agree 100%:

Hypothyroidism is one of the most over-diagnosed

diseases in pet bird medicine!

A low blood thyroid level is NOT definitive for hypothyroidism in pet birds. The blood thyroid levels fluctuate throughout the day and may just be low when the particular blood sample was taken. Also many general disease conditions can artificially lower the circulating blood thyroid levels. These are the two main reasons why hypothyroidism is so often misdiagnosed.

The diagnosis of hypothyroidism requires a thyroid stimulating hormone (TSH) stimulation assay which is two measurements of blood thyroid levels, one before TSH is administered and one 2-4 hours after administration. A normally functioning thyroid gland will cause a 3-fold increase in circulating Thyroid (TT4) hormone after TSH stimulation. Other physical changes that would support a diagnosis of hypothyroidism would include: marked generalized obesity, lipemic blood samples, depigmentation of feathers, lipomatous masses on body, pendulous abdomen, and feather loss.

Dr Rosenthal presented a case of an 18 year-old female Red-lored Amazon that presented with a history of chronic obesity, lipemia and failure to respond to dietary changes. The bird also had a pendulous abdomen and a cloacal fat mass that the bird began to mutilate which prompted the referral of this case to the University of Pennsylvania Veterinary College.

Blood chemistries could not be relied on because of the extremely lipemic sample. This bird was presumptively diagnosed as hypothyroidism as it also failed the TSH stimulation test. The bird did respond to thyroid medication, however, blood levels were still not stable 14 months after initiation of medication.


The true diagnosis of a hypothyroid pet bird requires several diagnostic tests and not just a response to thyroid medication. Thyroid medication will improve many conditions through its effect on various metabolic conditions within the bird's body. This profiled case does fit most conditions required in the diagnosis of hypothyroidism including a failure of the TSH stimulation test. However, Dr. Nemetz feels several diagnostic, as well as therapeutic, steps may have been left out in the medical management of this case. Chronic obesity can cause negative suppression of the thyroid gland, similar to obesity and its effect on the pancreas with the onset of Type II diabetes in humans and pet birds. The BIRD Clinic sees obese birds almost on a daily basis now for over 16 years and has managed better than 95% on diet management alone. Could better dietary management have helped this case without first placing the bird on thyroid supplementation? Could the thyroid gland respond to the TSH stimulation test once the obesity was controlled? If an animal is truly hypothyroid, it will need supplementation for the rest of its life. The take home message is to NOT simply accept a diagnosis of hypothyroidism in your pet bird without a thorough medical work-up and possibly a second opinion.