Thyroid Neoplasia in Captive Raccoons (Procyon lotor)

Abstract

Two adult, spayed, female raccoons were diagnosed with thyroid neoplasia. One raccoon had a palpable, left-sided, nonfunctional thyroid adenocarcinoma which was treated with a thyroidectomy twice with local recurrence both times. After the second recurrence, pulmonary metastases were identified. A third thyroidectomy was performed, and a vascular access port was placed for administration of intravenous doxorubicin. The raccoon developed pancytopenia and became anorexic after chemotherapy, and the owner elected humane euthanasia. The second raccoon had nonpalpable, bilateral, functional follicular thyroid adenomatous hyperplasia and was treated with a right thyroidectomy and a partial left thyroidectomy, leaving behind the grossly normal portion of the left thyroid. However, the animal was still hyperthyroid after surgery and was then successfully managed with topical methimazole gel. Thyroid pathology has been documented in raccoons in Europe, but is not reported in the United States. Thyroid neoplasia in raccoons can occur as a nonfunctional adenocarcinoma, as is commonly reported in dogs, or as a functional adenoma, as is commonly reported in cats. Raccoons with adenocarcinomas should be evaluated for pulmonary metastasis. Methimazole gel may be a viable treatment option for raccoons with hyperthyroidism.