Canine Adenoma - Carcinoma | Adenoma - Carcinoma in Dogs

Thyroid adenomas in dogs are usually small, nonfunctional masses that do not cause clinical signs and are found incidentally at necropsy. Exceptions are dog thyroid adenomas that are functional and cause hyperthyroidism or are unexpectedly identified during ultrasound examination of the ventral neck. In contrast, the more clinically common thyroid carcinomas in dogs are usually large, solid masses that cause clinical signs that can be recognized by owners and are easily palpated by clinicians.

Dog thyroid carcinomas frequently extend into the esophagus, trachea, cervical musculature, nerves, and thyroidal vessels. Distant metastasis to the lungs and retropharyngeal lymph nodes is common. Metastasis to other locations, including the liver, kidneys, heart base, bones and spinal cord, is also possible. Because of the high prevalence of malignancy, all thyroid masses discovered antemortem in the dog should be assumed to be malignant until proven otherwise.

Most dogs with thyroid tumors are euthyroid or hypothyroid; approximately 10% of dogs have functional thyroid tumors that secrete excess thyroid hormone, causing hyperthyroidism. Clinical signs of hyperthyroidism may predominate in these dogs. Hyperthyroidism may be caused by functional thyroid adenomas and carcinomas. In contrast, adenomatous hyperplasia is the most common cause of hyperthyroidism in cats but has not been described in dogs.

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Hypothyroidism is one of the most common canine endocrine disease and can be challenging to diagnose but is easily treated.

Causes

- Usually the result of lymphocytic thyroiditis or thyroid atrophy in dogs.
- Congenital thyroid hypoplasia (uncommon).
- Secondary hypothyroidism due to impaired pituitary secretion of thyrotropin.

Hypothyroidism in dogs - Canine Thyroid Disease Pathophysiology of hypothyroidism in dogs (most cases)

- Thyroid gland failure, with reduced secretion of thyroid hormones.
- Decreased active hormone available to enter cells.
- Gradual onset of cliical signs precipitated by insufficient thyroid hormone influence on metabolism, skin, reproductive system and neuromuscular system.
- Incresed pituitary secretion of thyrotropin in attempt to compensate.

Diagnosis

Canine hypothyroidism affects mostly middle-aged dogs and here's a list of predisposed breeds:

- Golden Retriever
- Doberman Pinscher
- Labrador Retriever
- Irish Setter
- Miniature Schnauzer
- Dachshund
- Cocker Spaniel
- Airedale Terrier

Physical Findings

- Alopecia, hyperpigmentation, dull coat without pruritis unless secondary pyoderma is present
- Bradicardia
- Neurologic abnormalities
- Weakness

Treatment Objectives

- Improve skin and coat quality
- Increase activity, decreas weight

The prognosis is good with treatment.