Hypothyroidism Flashcards Preview

Module 17 > Hypothyroidism > Flashcards

Flashcards in Hypothyroidism Deck (30)
Loading flashcards...
1
Q

what are the effects of thyroid hormones (4)

A
  1. metabolism: increases metabolic rate
  2. infant growth: cretinism
  3. hair growth: activates anagen
  4. others: cardiovascular, hemapoietic, orthopaedic
2
Q

how does the thyroid gland produce hormones

A

Consists of follicles which are lined by follicular cells which are full of colloid

Colloid is iodinated thyroglobulin

Thyroglobulin is made by the follicular cells using large numbers of tyrosine molecules that undergo iodination using the enzyme thyroid peroxidase

Thyroglobulin is broke down in the follicular cell and broken down through proteolysis to produce T4 — T3

3
Q

what is the difference between free T4 and total T4

A

In circulation there is a small amount of free thyroxine but about 99% of blood T4 is bound to protein

Can cross through membranes and get into cells and is converted to T3 —> which will have the effect in the cell

4
Q

how does the feedback loop of T4 work

A

Pituitary gland:

Produces TSH which stimulates the thyroid to produce T4 —> negative feedback loop

Excessive T4 is removed into rT3 if it needs to lower metabolic rate

Hypothalamus:

Releases TRH —> thyrotropin releasing hormone which stimulates pituitary to release TSH

Classic negative feedback loop

Higher centres of brain control both the pituitary and hypothalamus

Cortisol, IL-6, TNF-alpha, etc can influence the production of TRH, TSH and T

5
Q

what are the most common causes of hypothyroidism

A

Primary: most common form —> results from problems within the thyroid gland, usually destruction Lymphocytic thyroiditis (>90%) (immune-mediated destruction)

Will see increased levels of thyroid hormone autoantibodies in early stage of disease then will eventually see a decrease in T4 in the advanced stage

Idiopathic atrophy

Congenital (rare)

6
Q

what are non-thyroidal influences on thyroid hormones (3)

A
  1. physiological: age, breed, sex, time of day, time of year, obesity, starvation
  2. therapeutic: steroids, potentiated sulphonamides, diuretics, sedatives/anaesthetics
  3. pathological: sick euthyroid syndrome
7
Q

what other factors can cause non-thyroidal illness (4)

A
  1. starvation
  2. surgery/anesthesia
  3. neoplasia
  4. other endocrinopathies
8
Q

what are the causes of primary hypothyroidism (3)

A
  1. lymphcytic thyroiditis
  2. idiopathic atrophy
  3. congenital
9
Q

what breeds are predisposed to congenital hypothyroidism

A

Giant Schnauzer, Boxer

10
Q

what are the signs of congenital hypothyroidism

A

Disproportionate dwarfism

Cretinism

Hypothyroidism

11
Q

what breeds are predisposed to primary adult hypothyroidism

A

golden retriever, lab, doberman, boxer

12
Q

what are the stages of diagnosing hypothyroidism

A

history

clinical exam

routine blood tests

specific tests

trial therapy

13
Q

what are the clinical signs of hypothyroidism

A

Mental dullness

Lethargy

Exercise intolerance

Propensity to gain weight without corresponding increase in appetite or food intake

Cold intolerance

14
Q

what are the dermatological clinical signs of hypothyroidism

A

Classic cutaneous signs include:

Bilaterally symmetric, non-pruritic truncal alopecia that tends to spare the head and the extremities

Alopecia may be local or generalized and symmetric or asymmetric

Seborrhea and pyoderma

Dull hair coat, dry and easily epilated

Hair regrowth is slow

Hyperkeratosis leads to development of scales and dandruff

Hyperpigmentation

Myxedema (skin thickening)

Predominantly in the forehead and face of dogs resulting in rounding of the temporal region

Puffiness and thickening of the facial skin folds and drooping of upper eyelids

“Tragic facial expression”

15
Q

what are the cardiovascular changes seen with hypothyroidism

A

Bradycardia: small QRS complexes, weak apex beat

Arrhythmias

16
Q

what are the hematological changes seen

A

pale mucus membranes

non-regenerative normochromic anemia

17
Q

what reproductive abnormalities are seen

A

Persistent anestrus

Abortion

Inappropriate galactorrhea

18
Q

what neurological abnormalities are seen

A

Lower motor neurone disease

Peripheral vestibular syndrome

Laryngeal paralysis

Common in old labs as well as hypothyroidism

Megaesophagus

19
Q

what occular abnormalities are seen

A

Lipid effusion into aqueous humour

Corneal lipidosis

Chronic uveitis

Glaucoma (secondary)

Keratoconjunctivitis sica

20
Q

what are the common clinical manifestations

A

lethargy

weight gain

alopecia

pyoderma

seborrhea

21
Q

what are the uncommon clinical manifestations

A

neuromuscular disoders

female infertility

myxoedema

ocular disorders

congenital disease

22
Q

what are the clinical pathology can help confirm the diagnosis

A

cholesterol

triglycerides

PCV

CK

thyroid hormones

assays for TSH

assay for anti-thyroid antibodies

23
Q

what are the normal T4 levels

A

>35 nmol/l

24
Q

what is the grey zone of T4 levels

A

14-35 nmol/l

25
Q

what are the T4 levels that would indicate hypothyroid or sick euthyroid

A

0-14 nmol/l

26
Q

how can TSH be used to diagnose hypothyroid

A

with hypothyroidism there will be elevated TSH levels

reduction in feedback so TSH will increase and the thyroid is unable to repsond to it

27
Q

what is the best test to diagnose hypothyroidism

A

TSH stimulation

gold standard but human TSH very expensive

anaphylaxis is rare risk

28
Q

how can a low dose suppression test be used to exclude HAC

A

Used to exclude Cushing’s disease

As long as cortisol is suppressed and stays suppressed —> not Cushing’s

Hypothyroid dogs are not PUPD unlike Cushing’s

29
Q

what is used to treat hypothyroidism

A

sodium levothyroxine

0.02mg/kg SID or 0.01 mg/kg BID

30
Q

how would you monitor the therapy of a hypothyroidism

A

clinical improvement

trough or peak levels –> increase dose, SID dosing