“THE PEOPLE WHO GET ON IN THIS WORLD ARE THE PEOPLE WHO GET UP AND LOOK FOR THE CIRCUMSTANCES THEY WANT, AND IF THEY CAN’T FIND THEM, MAKE THEM.” - GEORGE BERNARD SHAW ATTITUDE

R EVIEW ENDOCRINE SYSTEM DISEASES

Master Endocrine gland: Hypothalamus REVIEW OF THE BASICS

Review of the basics Endocrine glands- basic units of the endocrine system.  Secrete hormones directly into the bloodstream.  Ductless glands. Exocrine glands- units that secrete their products onto epithelial surfaces through tiny tubes called ducts.

REVIEW OF THE BASICS

HORMONES Chemical messengers produced by endocrine glands and secreted directly into blood vessels. Produce effects when bound to their specific receptors on cells. – Each body cell has specific receptors to certain hormones (target).

HORMONES

Control of Hormone Secretion “Negative Feedback System” – If hormone is of adequate levels, gland will either slow or stop production of the hormone which is called negative feedback. Direct Stimulation of Nervous System – Secretion of some hormones is stimulated by sympathetic nerve impulses when an animal feels threatened. Fight or flight response from sympathetic nervous system

HYPERTHYROIDISM HYPOTHYROIDISM DISEASES OF THE THYROID GLAND

ANATOMY OF THE TYROID GLAND

Thyroid gland Gland not usually palpable Located at ventral cervical region along lateral margins of trachea Hormones produced by thyroid gland  T3 (Triiodothyronine) and T4 (tetraiodothyronine, thyroxine), iodine containing hormones.  Produced by follicular cells  Calcitonin – Causes calcium deposition in bone which decreases blood calcium concentrations  Produced by parafollicular cells

HYPOTHYROIDISM

Hypothyroidism MOST COMMON ENDOCRINE DISEASE IN DOGS; rare in cats  Breeds: Golden Retriever, Doberman, Irish Setter, Schnauzer, Cocker Spaniel, Dachshund, others 4-10 yrs of age Females

Hypothyroidism Definition: clinical state associated with deficiency of thyroxine, which causes low cell metabolism in most tissues of the body CAUSES:  Primary acquired – 90% of dogs  Caused by lymphocytic thyroiditis or idiopathic follicular atrophy  Also by iodine deficiency, neoplasia, infection  Secondary acquired- RARE  Anterior Pituitary dysfunction or destruction from neoplasia – leads to ↓TSH  Congenital Hypothyroidism-RARE

Hypothyroidism Clinical Signs – COMMON FINDINGS  Weight gain w/o diet change  Skin changes  Bilaterally symmetric truncal alopecia  Alopecia of the tail (rat tail), neck, axillae, and other areas of friction  Seborrhea  Superficial pyoderma  Dry, lusterless haircoat  Hyperpigmentation  Cold intolerance  Lethargy/sleeping  Exercise intolerance

Hypothyroidism

Clinical signs/Bloodwork results– Less common findings  Neuropathies – generalized weakness, ataxia, facial paralysis/paresis, seizures (secondary to cerebral atherosclerosis)  GI upset – Constipation, Regurgitation caused by megaesophagus  Bloodwork abnormalities – hyperlipidemia is most common, gross lipemia ( milky appearance to the serum), hypercholesterolemia (80%), anemia (mild non-regenrative)  Eye – hyperlipidemia => corneal lipidosis and anterior uveitis

Hypothyroidism: DIAGNOSIS Blood Tests  Hypothyroid dogs have lowered level of T4  Test total T4(TT4), +/- T3 levels  Free T4: Free T4 is thyroxine that is not protein bound (ED is most accurate test for fT4 measurement)  Basal TSH concentration  Measures TSH in blood, should be used in conjunction with other tests and clinical signs *ED = equilibrium dialysis

Hypothyroidism: Considerations Remember sick animals and animals on certain medications (anti-epileptics) may have depressed T4 levels. (Euthyroid sick syndrome)  Wait and re-test after treatment of underlying cause if clinical signs persist. Greyhounds and Scottish deerhounds have low T4 levels naturally; treat if clinically evident.

Hypothyroidism Treatment  Thyroid supplement – L-thyroxine  Oral, synthetic levothyroxine  Daily administration  Steady state levels – 4 wks  Test levels and adjust dose until T4 normal Want to test 4-6 hours after dose is given (when serum levels are highest)

Thyroid replacement hormone (levothyroxine sodium)

Hypothyroidism Client Education  Supplement for life  Daily dosing (usually BID) required  Overdose => hyperthyroidism  Vet may recommend a reduced fat diet until body weight is satisfactory and T4 levels are normal.

HYPERTHYROIDISM

Hyperthyroidism Definition: Pathologic, sustained, high overall metabolism caused by high circulating concentrations of thyroid hormones Most common Endocrine disease in cats (one of the big 3 diseases of older cats)  Very rare in dogs Pathophysiology  Autonomously hyperfunctioning nodules, no physiologic controls (functional thyroid adenoma)  Secrete T4 and T3

Hyperthyroidism in cats Since 2007, the prevalence of hyperthyroidism in cats has increased by 19% in mature adult cats, and by 13% in geriatric cats.

Hyperthyroidism Clinical Signs  Multi-systemic: reflects increase in metabolism  Weight loss  Polyphagia  Vomiting/diarrhea  Polydipsia/ polyuria  Tachypnea/dyspnea  Hyperactivity  Aggression

Hyperthyroidism Clinical signs  Reflect increase in metabolism  Tachycardia +/- heart murmur (thickening of LV and heart muscle)  Hypertension  Poor body condition  Thickened nails  Unkempt appearance  Large (palpable) thyroid gland 70% - bilateral

Hyperthyroid cat Middle age to older catsBlindness with retinal detachment Wt lossPalpable enlarged Thyroid gland PolyphagiaAggressive Tachycardia unkempt haircoat

Hyperthyroid cat: Goiter

Hyperthyroidism Diagnosis  Palpate enlarged thyroid gland  Elevated T4, FT4  X-rays for associated heart disease

Hyperthyroidism: Scintigraphy Normal cat Normal uptake in salivary glands and thyroid glands Hyperthyroid cat Unilateral thyroid adenoma

Hyperthyroidism: Scintigraphy Hyperthyroid cat Bilateral thyroid adenoma Hyperthyroid cat Ectopic (intrathoracic) thyroid adenoma Hyperthyroid cat Functional thyroid carcinoma (represents regional metastasis)

Hyperthyroidism Treatment  Methimazole (Tapazole) – anti-thyroid drug – block incorporation of iodine into thyroglobulin.  COMMON AND PRACTICAL FOR CLIENTS  Radioiodine treatment – I 131  Effective  Emitted radiation destroys functioning follicular cells  TREATMENT OF CHOICE  Surgical removal of gland  May cause hypothyroidism  May result in hypocalcemia due to hypoparathyroidism

Hyperthyroidism: Medical Rx METHIMAZOLE ORAL PILL, BUT CAN BE FORMULATED INTO A TRANSDERMAL OINTMENT OR FLAVORED TREAT

Hyperthyroidism Complications  Renal disease/failure unveiled when thyroid levels controlled  2-3 months after medication started  Occasionally tapazole will no longer be effective usually after 2-3 years of treatment Prognosis  Excellent if uncomplicated  If labs show azotemia prior to treatment, prognosis more guarded

Hyperthyroidism: Client Info Cause of disease is unknown Surgery or Radiation are only cures Cat may become hypothyroid following Rx – usually not clinically significant and supplementation can be initiated if necessary Following Tapazole, Blood pressure and kidney values should be checked routinely Clinical case: Quiz-A-dyspneic-cat-with-hyperactivity-and- f/ArticleStandard/Article/detail/750137?contextCategoryId=48035