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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 can’t find them, make them.” - George Bernard Shaw
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ENDOCRINE SYSTEM DISEASES
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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. Circulate throughout body and produce effects when attach to receptors in or outside of cells. – Ductless glands. Exocrine glands- units that secrete their products onto epithelial surfaces through tiny tubes called ducts.
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Chemical messengers produced by endocrine glands and secreted directly into blood vessels. Produce effects when find their receptors in or on cells. – Each body cell has specific receptors to certain hormones (target). – If body does not have receptor, hormone will pass by. – Only certain hormones can fit to receptors and when it occurs, then it changes the activity of the cell. Hormones
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Control of Hormone Secretion “Negative Feedback System” – Endocrine glands will be stimulated to produce more hormone when it drops below a certain amount in the body. – 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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Hypothyroidism
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Thyroid gland Gland not usually palpable Located at ventral cervical region along lateral margins of trachea Hormones produced – 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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Control of thyroid hormone production Thyrotropin releasing hormone
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Hypothyroidism Definition: clinical state associated with deficiency of thyroxine, which causes low cell metabolism in most tissues of the body – 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 cretinism
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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 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 (why?) – Lethargy/sleeping – Exercise intolerance
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Hypothyroidism
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Clinical signs/Bloodwork results– Less common findings – Neuropathies – generalized weakness, ataxia, facial paralysis/paresis, seizures (secondary to cerebral atherosclerosis) – GI – 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 *Virtually all body systems are affected, clinical signs are generally non-specific
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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; diagnose based on clinical signs as well as test results; 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 => hyperthyroidism Regular rechecks are recommended including bloodwork. PU/PD; nervousness, weight loss, panting, weakness, inc. appetite – Vet may recommend a reduced fat diet until body weight is satisfactory and T4 levels are normal.
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Hypothyroidism clinical case http://www.idexx.com/view/xhtml/en_us/sm allanimal/education/reference-library/case- studies/200810case-study.jsf?SSOTOKEN=0
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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 cont’d – 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 catsBlindness with retinal detachment Wt lossPalpable enlarged Thyroid gland PolyphagiaAggressive 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 – 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
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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.com/vetmed/Medicine/Image-Quiz-A- dyspneic-cat-with-hyperactivity-and- f/ArticleStandard/Article/detail/750137?contextCategoryId=48035
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