Med I - Feline Hyperthyroidism

Front 1

Hyperthyroidism
-definition

Back 1

-clinical condition resulting from excessive production and secretion of thyroxine (T3) and triiodothyroxine (T4)

Front 2

Primary Hyperthyroidism
-signalment

Back 2

-common in cats
-middle aged and older (>10 yrs)
-no breed or gender predilection
-arises in gland independent of hypothalamus or pituitary

Front 3

Primary hyperthyroidism
-pathology

Back 3

Benign thyroid tumors
-Multinodular adenomatous goiter** (both lobes)
-Adenoma

Malignant thyroid tumors
-Thyroid carcinoma (1-3%)

Front 4

Primary hyperthyroidism
-etiology

Back 4

No definitive

Nutritional/Environmental:
-canned food, flavors, can types
-indoors
-PBDEs (polybrominated diethyl ethers)

Speculated:
-Autocrine/Paracrine growth factors
-Circulating thyroid stimulators (immunoglobins binding to TSH receptors [graves disease])

Front 5

Thyroid hormone actions

Back 5

-thermoregulation & heat production
-carbohydrate, protein, lipid metabolism
-CNS activity
-Sympathetic NS activity

Front 6

Hyperthyroidism
-physiological effects

Back 6

-Inc. energy expenditure
-CNS and smooth muscle stimulation
-Inc. myocardial contractility
-Inc. HR
-Enhanced blood flow

Front 7

Hyperthyroidism

Inc. energy expenditure:
-results in
-clinical effects

Back 7

Results in:
-Inc. food intake
-Inc. stored energy utilization
-Inc. oxygen consumption

Clinical effects:
-weight loss
-polyphagia

Front 8

Hyperthyroidism

CNS and smooth muscle stimulation:
-results in:
-clinical effects

Back 8

Results in:
-GI hypermotility
-CRTZ stimulation

Clinical effects:
-changing defecation
-vomiting (but will eat again)

Front 9

Hyperthyroidism

Inc. myocardial contractility and inc. heart rate:
-results in
-clinical effects

Back 9

Inc. myocardial contractility:
-inc. cardiac beta adrenergic receptors

Inc. heart rate:
-indirect effect of increased metabolic demands

Clinical effects
-cardiac thyrotoxicosis
-systemic hypertension

Front 10

Hyperthyroidism

Enhanced blood flow secondary to CV changes
-result in
-clinical effects

Back 10

Result in:
-inc. blood volume
-inc. renal blood flow and GFR
-relationship between hyperthyroidism and chronic kidney dz

Clinical effects:
-PU/PD

Front 11

Hyperthyroidism
-common history

Back 11

-weight loss
-polyphagia

-unkempt hair
-PU/PD
-vomiting
-diarrhea
-hyperactivity

Front 12

Hyperthyroid
-physical exam

Back 12

-palpable thyroid nodule
-low BCS
-abnormal heart sounds (tachycardia, murmur, arrhythmia)
-fractious
-overgrown nails
-sunken eyes

Front 13

Hyperthyroidism
-differentials

Back 13

-chronic kidney disease
-diabetes mellitus

Front 14

Difference between signs for hyperthyroidism and chronic kidney disease

Back 14

-cat will have a poor appetite with chronic kidney disease

Front 15

Diabetes mellitus
-clinical signs

Back 15

-possible polyphagia but uncommon
-PU/PD

Front 16

Hyperthyroidism
-methods of diagnosis

Back 16

-hormone measurements
-minimum database
-cardiac evaluation
-technetium (99Tc) Scan

Front 17

Hyperthyroidism
-diagnosis via hormone measurements

Back 17

Demonstrate elevated total or free T4

-Random basal serum total T4** (very reliable)

-Free T4 if determined via equilibrium dialysis method

Front 18

Hyperthyroidism
-minimum data base

Back 18

CBC
-erythrocytosis (inc. Epo production from inc. O2 consumption)

Serum chemistry
-hyperglycemia (stress, concurrent DM)
-azotemia (primary kidney Dz)
-Elevated ALT, ALP (reversible)

Urinalysis
-occult UTI
-low specific gravity (kidney disease, inc. blood flow, DM)

Front 19

Hyperthyroidism
-cardiac evaluation should be completed when

Back 19

-respiratory distress
-tachypnea
-muffled heart sounds
-tachycardia --> cardiomegaly
-arrhythmias
-murmurs

Front 20

Hyperthyroidism
-idea behind Technetium Scan

Back 20

-thyroid gland uptake of 99Tc is strongly sorrelated with circulating thyroid hormone concentration

Front 21

Technetium (99Tc) Scan
-useful for diagnosing

Back 21

-bilateral vs. unilateral thyroid disease
-ectopic thyroid tissue
-non-palpable thyroid tissue
-occult hyperthyroidism
-metastatic thyroid tissue

Front 22

Technetium Scan
-normal T:S ratio

Back 22

1.6

Thyroid:Salivary

Front 23

Feline Hyperthyroidism
-diagnostic dilemmas

Back 23

-occult hyperthyroidism
-apathetic hyperthyroidism
-concurrent chronic kidney disease

Front 24

Occult hyperthyroidism
-define
-explanations

Back 24

-exam findings consistent with hyperthyroidism but total T4 is normal

Explanations:
-disease caught early
-fluctuating hormone conc.
-concurrent nonthyroid illness causing falsely decreased total T4

Front 25

Does normal thyroid T4 rule out hyperthyroidism?

Back 25

-NO

Front 26

Ways to test occult hyperthyroidism

Back 26

-technetium scan
-T3 suppression test

Front 27

Apathetic hyperthyroidism
-clinical signs

Back 27

-depression no hyperactivity
-anorexia not polyphagia
-marked weight loss

Front 28

Apathetic hyperthyroidism
-possible concurrent signs

Back 28

-CHF
-neoplasia
-CKD

Front 29

Chronic kidney disease
-signalment

Back 29

-common in older cats

Front 30

Chronic kidney disease
-clinical signs

Back 30

-PU/PD
-weight loss
-lethargy
-inappetance

Front 31

How can hyperthyroidism mask chronic kidney disease?

Back 31

-inc. renal blood flow
--inc. GFR
---dec. serum creatinine
----non-azotemic CKD

Front 32

Chronic kidney disease
-how to determine if concurrent with hyperthyroidism

Back 32

-Palpation (kidneys small and irregular)
-Urine specific gravity (not concentrated with CKD, possible concentrated with hyperthyroidism)
-Serum chemistry (azotemia can be due to dehydration or CKD)
-abdominal imaging
-Methimazole trial

Front 33

Feline hyperthyroidism
-treatment options

Back 33

-Medical management
-Radioactive iodine**
-Surgical thyroidectomy (not recommended)

Front 34

Methimazole
-describe

Back 34

-concentrates in the thyroid gland and prevent thyroid hormone production
-oral or transdermal application
-life long

Front 35

Methimazole
-side effects

Back 35

-GI
-Facial pruritis
-hepatotoxicity
-IMHA
-agranulocytosis
-thrombocytopenia

Front 36

Methimazole
-clinical indications for use

Back 36

-owner financial concerns
-stabilization before 131I therapy
-suspect CKD (treat until euthyroid and assess if candidate for 131I therapy)

Front 37

Is a methimazole trail a perfect predictor of CKD presence?

Back 37

-no

Front 38

Radioactive iodine therapy
-function

Back 38

-iodine specifically targets hyperactive thyroid tissue

Front 39

Radioactive thyroid therapy
-patient selection

Back 39

-stable hyperthyroidism
-concurrent illnesses addressed
-patient acclimates to the hospital

Front 40

Radioactive iodine
-reasons for treatment failure

Back 40

-thyroid carcinoma
-unilateral disease
-low 131I dose

Front 41

Surgical thyroidectomy
-when is it reasonable

Back 41

-no ectopic thyroid tissue
-unilateral thyroid disease

Front 42

Surgical thyroidectomy
-advantages

Back 42

-possibly curative
-minimal oral meds

Front 43

Surgical thyroidectomy
-disadvantages

Back 43

-invasive
-anesthesia risk
-hypoparathyroidism
-hypothyroidism

Front 44

Feline hypothyroidism
-prognosis

Back 44

-curable

Depends on:
-physical condition
-concurrent disease
-benign vs. malignant
-treatment options