Sky, a 13-year-old male neutered domestic short hair cat, presented to Animal Imaging for thyroid scan prior to receiving treatment with I-131 therapy. He has a history of uncontrolled hyperthyroidism and weight loss regardless of increasing Methimazole dosing. His T4 was 27.4 ug/dL at the time of thyroid scan and he had a systolic heart murmur appreciable on intake auscultation. He was injected with intravenous administration of a radionucleotide substance at a standardized dose and images were collected 20 minutes after injection.
The results of the thyroid scan are shown below.
The red arrow points to the increased uptake within the thyroid gland and the blue arrows points to the level of the salivary glands. The salivary glands are used as a standardized area of uptake to allow for proportional relationship to the thyroid gland. This relationship allows us to determine the degree of abnormal thyroid activity in any given patient. In this particular patient, unilateral, smooth, increased uptake of the right thyroid gland is seen.
Pictured below is an image of bilateral, smooth increased uptake of the nucleotide substance in a thyroid gland in another hyperthyroid cat.
As you can see, these two cats have 2 different presentations of thyroid disease. A value of using nuclear scintigraphy for hyperthyroidism is that this modality allows for proportional, individualized dosing of I-131 to treat the patient. Many owners of hyperthyroid cats seek I-131 therapy as a way to avoid having to administer daily oral medication to their pet. The specific dosing of the therapy to the patient helps to minimize risks, such as inducing hypothyroidism. Hypothyroidism would require oral medication for the rest of the cat’s life to treat, often defeating the reason many owners seek I –131 treatment to start.
In addition, the appearance of the uptake, for example, unilateral or bilateral, informs the veterinarians and owners about the likelihood of benign vs malignant disease, the need for additional diagnostics or staging, and the likelihood of retreatment with I-131 therapy being needed. When deciding if I-131 therapy is the right decision for either your pet or patient, considering a thyroid scan can offer individualized dosing to improve patient care and positive outcomes for owners.
