Page 1949 - Cote clinical veterinary advisor dogs and cats 4th

Thyroid Neoplasia 975

PROGNOSIS & OUTCOME PEARLS & CONSIDERATIONS Client Education
For dogs with megaesophagus, provide client
Comments
VetBooks.ir • Resectable thymoma without megaesopha- • It is critical to differentiate thymoma from Feedings. Diseases and Disorders
Dog:
education sheet: How to Provide Elevated
gus
mediastinal lymphoma, especially in cats,
○ 70%-80% 1-year survival rate, 50% 3-year
survival in one study; 55% 1-year, 44% because the former is surgically treated and SUGGESTED READING
the latter is treated medically.
Zitz JC, et al: Results of excision of thymoma in cats
2-year, 44% 3-year, and 44% 4-year • Adjuvant radiation therapy ± chemotherapy and dogs: 20 cases (1984-2005). J Am Vet Med
survival in another study. Median survival may benefit animals with nonresectable Assoc 232:1186, 2008.
time is 616-635 days. thymoma.
• Nonresectable thymoma: poor • Closely monitor animals for development of AUTHORS: MaryAnn G. Radlinsky, DVM, MS, DACVS;
Don R. Waldron, DVM, DACVS
• Presence of myasthenia gravis or megaesopha- aspiration pneumonia and myasthenia gravis. EDITOR: Elizabeth A. Swanson, DVM, MS, DACVS
gus: guarded to poor; may resolve over a
period of months Technician Tips
Cat: • Knowledge of and experience in working
• Resectable thymoma with thoracostomy tubes is important in the
○ 70% 1-year, 63% 2-year, 63% 3-year, and postoperative management of patients who
47% 4-year survival rates. Median survival have undergone a thoracotomy.
is 1354 days. • Patients with megaesophagus will require
nutritional support (p. 1109).

Thyroid Neoplasia Client Education
Sheet

BASIC INFORMATION • Histologic subtypes surgery or radiation therapy (RT) for local
○ Follicular cell origin: includes compact disease.
Definition (solid), follicular, anaplastic, and papillary; • Metastasis present in 30%-40% at time of
Cancer of the thyroid gland in dogs is most first two constitute majority in dogs presentation, 80% at time of death
often carcinoma or adenocarcinoma and may ○ Parafollicular (i.e., C-cell or medullary • Increased metastasis risk with tumors
3
(10%) or may not (90%) be functional, causing thyroid) carcinomas; have a lower meta- > 23 cm ; metastasis almost 100% if tumor
3
hyperthyroidism. This chapter deals specifically static rate > 100 cm and with bilateral tumors
with thyroid tumors in dogs. • Can be classified as functional (secretes
thyroid hormones) or nonfunctional DIAGNOSIS
Epidemiology
SPECIES, AGE, SEX HISTORY, CHIEF COMPLAINT Diagnostic Overview
• Most often occurs in older dogs Common clinical signs: Malignant thyroid neoplasia is diagnosed using
• Thyroid neoplasia in cats is rarely (2% of • Visible or palpable mass in ventral neck exam findings (e.g., mass location), cytology,
cases) malignant, as discussed on p. 503. • Dysphonia and imaging. Due to high vascularity, signifi-
• Dyspnea cant bleeding can occur during aspiration or
GENETICS, BREED PREDISPOSITION • Dysphagia biopsy. Test sequence is very important because
• Increased expression of genes encoding • Unexplained weight loss, if functional some tests can interfere with evaluation and
proteins involved in a major cell survival treatment.
pathway (PI3K/AKT) occurs in some dogs. PHYSICAL EXAM FINDINGS
• Predisposed breeds include beagles, golden • Palpable mass in mid-cervical region, Differential Diagnosis
retrievers, boxers, and Siberian Huskies. unilateral or bilateral • For a cervical mass
• Masses can occur between base of the tongue ○ Other primary tumors: lipoma (p. 591),
RISK FACTORS and the base of the heart but usually in soft-tissue sarcoma, mast cell tumor (pp.
• Radiation exposure cranial to middle, ventral neck; occasion- 632 and 634), or lymphoma (p. 609);
• Untreated hypothyroidism ally intimately associated with larynx or carotid body tumor if tumor located high
sublingual region (cranial) on neck
ASSOCIATED DISORDERS • Nodal enlargement of mandibular and ○ Metastatic oral tumor
• Hyperthyroidism (p. 503) superficial cervical lymph nodes if metastases ○ Abscess
• Hypothyroidism (p. 525) present ○ Salivary mucocele
• Uncommonly, part of multiple endocrine • Referred upper airway noise on thoracic
neoplasia syndrome auscultation Initial Database
• Laryngeal paralysis (p. 574) • CBC, chemistry, urinalysis for general health
• Horner’s syndrome Etiology and Pathophysiology assessment; fasting hypercholesterolemia can
• Increased circulating thyroid-stimulating occur with hypothyroidism.
Clinical Presentation hormone (TSH) is associated with an • Thyroid panel (total T 4, free T 4 by equilib-
DISEASE FORMS/SUBTYPES increased risk of thyroid cancer (untreated rium dialysis method, and TSH) (p. 525)
• Benign adenoma in dogs very uncommon hypothyroid beagles) and tumor relapse • Cytology of mass
(<10%); usually silent and are found (humans). In dogs, thyroid supplementation ○ Significant bleeding can occur.
incidentally to suppress TSH is typically combined with ○ Sample can be hemodiluted.

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