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ATTITUDE

• The people who get on in this world are the
  people who get up and look for the circumstances
  they want, and if they cant find them, make
  them.
• -George Bernard Shaw

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ENDOCRINE SYSTEM DISEASES

• review

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REVIEW OF THE BASICS
Master Endocrine gland Hypothalamus
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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.

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REVIEW OF THE BASICS
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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).

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HORMONES
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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

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DISEASES OF THE THYROID GLAND

• HYPERTHYROIDISM
• HYPOTHYROIDISM

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ANATOMY OF THE TYROID GLAND
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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

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HYPOTHYROIDISM
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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

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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

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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

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Hypothyroidism
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Hypothyroidism
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Hypothyroidism
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Hypothyroidism
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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 gt corneal lipidosis and
  anterior uveitis

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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
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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.

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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)

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Thyroid replacement hormone (levothyroxine
sodium)
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Hypothyroidism

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

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HYPERTHYROIDISM
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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

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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.
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Hyperthyroidism

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

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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

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Hyperthyroid cat
Middle age to older cats Blindness with retinal
detachment Wt loss Palpable enlarged Thyroid
gland Polyphagia Aggressive Tachycardia
unkempt haircoat
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Hyperthyroid cat Goiter
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Hyperthyroidism

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

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Hyperthyroidism Scintigraphy
Normal cat Normal uptake in salivary glands and
thyroid glands
Hyperthyroid cat Unilateral thyroid adenoma
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Hyperthyroidism Scintigraphy
Hyperthyroid cat Bilateral thyroid adenoma
Hyperthyroid cat Ectopic (intrathoracic) thyroid
adenoma
Hyperthyroid cat Functional thyroid
carcinoma (represents regional metastasis)
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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

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

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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 http//veterinarymedicine.dvm360.co
  m/vetmed/Medicine/Image-Quiz-A-dyspneic-cat-with-h
  yperactivity-and-f/ArticleStandard/Article/detail/
  750137?contextCategoryId48035