NAVLE Endocrine

Canine Hypothyroidism Study Guide

Hypothyroidism is the most common endocrinopathy in dogs, characterized by inadequate production and secretion of thyroid hormones (T4 and T3) by the thyroid gland.

Overview and Clinical Importance

Hypothyroidism is the most common endocrinopathy in dogs, characterized by inadequate production and secretion of thyroid hormones (T4 and T3) by the thyroid gland. This condition affects virtually every organ system due to the fundamental role thyroid hormones play in cellular metabolism, making it a high-yield topic for the NAVLE examination.

The disease typically affects middle-aged dogs (mean age 7 years) and has a strong breed predisposition. Understanding the pathophysiology, clinical presentation, diagnostic approach, and treatment monitoring is essential for successful management of hypothyroid patients.

High-YieldHypothyroidism is one of the most OVERDIAGNOSED diseases in dogs. Never diagnose based solely on a low T4 value. Always correlate clinical signs with multiple thyroid function tests.
Parameter T4 (Thyroxine) T3 (Triiodothyronine)
Production Site 100% from thyroid gland 20% thyroid, 80% peripheral conversion
Biologic Activity Prohormone (less active) Active hormone (3-5x more potent)
Half-Life 10-16 hours 5-6 hours
Protein Binding Greater than 99% bound Greater than 99% bound

Anatomy and Physiology

Thyroid Gland Anatomy

The canine thyroid gland consists of two lobes located on either side of the trachea in the cervical region, caudal to the larynx. Unlike humans, dogs do not have an isthmus connecting the two lobes. The gland is composed of follicular cells that synthesize and secrete thyroid hormones and parafollicular C-cells that produce calcitonin.

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