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.