Download Hyperthyroid cat - Dr. Roberta Dev Anand

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
ENDOCRINE SYSTEM DISEASES
Master Endocrine gland: Hypothalamus
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.
Hormones
• 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
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
DISEASES OF THE THYROID GLAND
HYPERTHYROIDISM
HYPOTHYROIDISM
Hypothyroidism
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
Control of thyroid hormone
production
Thyrotropin releasing hormone
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
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
• 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
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 – 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
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; diagnose based on clinical
signs as well as test results; 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
• 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.
• Hypothyroidism clinical case
• http://www.idexx.com/view/xhtml/en_us/sm
allanimal/education/reference-library/casestudies/200810case-study.jsf?SSOTOKEN=0
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
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•
•
•
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Weight loss
Polyphagia
Vomiting/diarrhea
Polydipsia/ polyuria
Tachypnea/dyspnea
Hyperactivity
Aggression
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
Hyperthyroid cat
Middle age to older cats
Wt loss
Polyphagia
Tachycardia
Blindness with retinal detachment
Palpable enlarged Thyroid gland
Aggressive
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 – 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 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-Adyspneic-cat-with-hyperactivity-andf/ArticleStandard/Article/detail/750137?contextCategoryId=48035