Hypothyroidism in Dogs

Hypothyroidism in Dogs

• Definition: Thyroid hormone deficiency, leading to decreased metabolic rate.
• Prevalence: Common disease in dogs, particularly females aged 6-10 years.
• Genetic Predisposition: Certain breeds are more prone, including Golden Retrievers, Labs, Dobermans, Irish Setters, Miniature Schnauzers, Spaniels, Dachshunds, Cocker Spaniels, and Airedale Terriers.
• Causes (95% of cases): Primarily destruction of the thyroid gland itself, often due to lymphocytic thyroiditis (autoimmune disease) or idiopathic atrophy. Secondary causes (less common) include tumors or congenital conditions.

Clinical Signs of Hypothyroidism in Dogs

• Metabolic & Dermatological Signs:
  • Lethargy
  • Weight gain
  • Altered skin/coat: alopecia (hair loss), excessive shedding, dry skin. Hair loss on the tail is common ("rat tail").
  • Sun seeking behavior
  • Recurrent skin infections (UTIs)
  • Reproductive problems (anestrus)

Hypothyroidism in Dogs - Diagnosis

• Clinical Signs: Careful attention to symptoms, especially weight gain and lethargy.
• Blood Tests:
  • Possible hypercholesterolemia.
  • Low levels of T3 and free T4.
  • High levels of Thyroid Stimulating Hormone (TSH).

Hypothyroidism in Dogs - Treatment

• Lifelong Hormone Replacement: Supplementing with thyroid hormone.
• Oral Medication (BID): Typically successful.
• Dosage Monitoring: Regular monitoring is essential to adjust dosage as needed.
• Regular Checkups: Recheck blood work 1-2 times yearly after stabilizing treatment.
• Treatment Success Indication: Clinical improvement.

Hyperthyroidism in Cats

• Prevalence: Common disease in middle-aged and older cats.
• Causes: Excess of T3 and T4 due to thyroid adenoma (tumor) or possibly thyroid carcinoma.
• Diagnosis:
  • Increased T4 in serum chemistry is diagnostic if clinical signs are present.
  • If high but no clinical signs, recheck in two weeks.
  • Enlarged thyroid glands may be palpable.
  • Diagnositic imaging (e.g. ultrasound) or scintigraphy (nuclear imaging) might be used to confirm diagnosis.

Clinical Signs of Hyperthyroidism in Cats

• Weight loss
• Polyphagia (increased appetite)
• Occasional Vomiting
• Increased Appetite
• Tachycardia (rapid heart rate) with or without a murmur.
• Hypertension (high blood pressure)
• Blindness and retinal detachment
• Increased vocalization, especially at night.

Hyperthyroidism in Cats - Treatment

• Radioactive Iodine (I-131): Curative treatment of choice, simple, effective. Requires hospitalization while radioactive material is removed from the body.
• Antithyroid Drug Therapy: Daily, lifelong medications to block hormone synthesis. Medication examples are: methimazole and carbimazole.
• Diet (lifelong): Iodine-deficient diet, indicated if not a candidate for radioiodine treatment or surgery. No treats, prey or scraps allowed with this diet.
• Surgery (Thyroidectomy): Thyroid gland removal. Potentially curative but with anesthesia risks. Requires competent surgeon to remove the thyroid gland while sparing adjacent parathyroid glands. Supplementation with thyroid hormone will be required after surgery.

Hyperthyroidism - Complications

• Thyrotoxic hypertrophic cardiomyopathy: A heart disease.
• Systemic hypertension: High blood pressure.
• Chronic kidney disease (CKD): A common complication.

Explore the causes, symptoms, and prevalence of hypothyroidism in dogs. This quiz covers the clinical signs, genetic predispositions, and common breeds affected by this condition. Test your knowledge on this crucial health issue for canines.