“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

REVIEW

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

HYPERTHYROIDISMHYPOTHYROIDISM

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 ageFemales

HypothyroidismDefinition: 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

Hypothyroidism

Hypothyroidism

Hypothyroidism

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

TreatmentThyroid supplement – L-thyroxine

Oral, synthetic levothyroxine Daily administration

Steady state levels – 4 wksTest 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 signsReflect 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 cats Blindness with retinal detachmentWt loss Palpable enlarged Thyroid glandPolyphagia AggressiveTachycardia unkempt haircoat

Hyperthyroid cat: Goiter

Hyperthyroidism

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

Hyperthyroidism: Scintigraphy

Normal catNormal uptake in salivary glandsand thyroid glands

Hyperthyroid catUnilateral thyroid adenoma

Hyperthyroidism: Scintigraphy

Hyperthyroid catBilateral thyroid adenoma

Hyperthyroid catEctopic (intrathoracic)thyroid adenoma

Hyperthyroid catFunctional 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 – I131 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 unknownSurgery 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: http://veterinarymedicine.dvm360.com/vetmed/Medicine/Image-Quiz-A-dyspneic-cat-with-hyperactivity-and-f/ArticleStandard/Article/detail/750137?contextCategoryId=48035