Diagnosis & Treatment Of Endocrine Disease 2

thyroidism & adrenocorticism

Examples of thyroid diseases

Hypothyroidism
Hyperthyroidism
Goitre

How do you test for thyroid function?

TSH levels —> show if thyroid is functioning normally or not

What can be tested for in blood tests to diagnose thyroid disease?

- Total T4
- Free T4
- Canine TSH
- Thyroglobulin autoantibodies

What indicates hyperthyroidism from a blood test?

High serum T4

Common clinical signs of hyperthyroidism

(most common in old cats)

Thin but ravenously hungry

Intermittent V+

Irritated/restless

Seaking heat

Coat sticks up/feels rough or greasy

How can hyperthyroidism be treated?

Remove thyroid tissue

- surgery —> thyroidectomy (risks removal of parathyroid gland also —> can induce hypocalcaemia)

- radioactive iodide

Reduce thyroid hormone synthesis

- restrict iodine

- block iodine synthesis

What are the risks of surgical thyroidectomy?

- upfront cost vs ongoing treatment
- damage to parathyroid gland —> can induce hypocalcaemia

How does radioactive iodine work to treat hyperthyroidism?

- Destroys thyroid follicles —> kills overactive thyroid cells, leaves normal thyroid tissue behind
- T3 & T4 levels normalise after 1-2 weeks
- Animals hospitalised for 1-4 weeks
- Excreta handled carefully (radioactive)
- Very expensive!

no recovery time, special diets or medications needed after

Describe how stopping synthesis of thyroid hormone is achieved

Use medication that prevents T3 & T4 being produced —> Methimazole

Methimazole can be transdermal gel or an oral product

Carbimazole —> used as oral product & metabolised into methimazole in gut —> given 15mins before food, strict dosing, risk of overdose (hypothyroidism)

In what species can you restrict dietary access to iodine to treat hyperthyroidism?

Cats

causes thyroid hormone to not be synthesised

cat needs to ONLY eat this type of food —> not always feasible for outdoor cats

cheapest option

What do thioureylenes do? What is the thioureylene that is licenced in the UK?

Block iodine synthesis

Carbimazole

Clinical signs of hypothyroidism

(most common in dogs)

Inactive

Coat falling out/not re-growing —> thyroid hormone not stimulating fur regrowth

“Tragic look”

Very overweight but don’t eat much

Recurring infections (esp. in ear) due to suppressed immune system

What are the two ways dogs can get hypothyroid?

Lymphocytic thyroiditis —> immune mediated disease

OR

Idiopathic thyroid gland atrophy —> less common

What indicates hypothyroidism on a blood test?

Free T4 —> more sensitive

Endogenous canine TSH —> expected to be increased i.e. trying to get thyroid gland to work

Thyroglobulin autoantibodies —> test for immune mediated disease

Low T4, high TSH is diagnostic

What is sick euthyroid syndrome?

Any patient with acute, severe illness may have abnormal thyroid function tests
- fall in total and free T3 levels
- normal T4
- normal TSH

aka low T3 syndrome

usually starvation, severe respiratory disease or pregnancy without the thyroid being diseased

How can hypothyroidism be treated?

Thyroid hormone replacement therapy (thyroid hormone replaced exogenously)

–Levothyroxine is (T4) —> given orally, 30mins before food

–Liothyronine (T3) —> only given to dogs not responding well to T4

Take time to get dosage correct

Adverse effects of thyroid hormone replacement therapy?

- Hyperthyroidism
- V+ & D+

- Itchy (pruritic)

- Anorexic (not eating anything)

How can disorders of the adrenal gland be diagnosed?
- Specific blood tests
- Non specific blood tests
- Specific dynamic tests

Specific Blood Tests

cortisol

aldosterone

ACTH

Non Specific Blood Tests

electrolytes

glucose

lipids

Specific Dynamic Tests

Dexamethazone suppression test

ACTH stimulation test

What are the types of hyperadrenocorticism (Cushings disease)?

Spontaneous

- Pituitary Dependent Hyperadrenocorticism (PDH)

- Adrenal Dependent Hyperadrenocortcism (FAT; functioning adrenal tumour)

Iatrogenic

overuse of medication

Blood tests for hyperadrenocorticism

Serum biochemistry (increased glucose, increased cholesterol)

Insulin impairment

Lipolysis activation

Haematology (decreased lymphocytes, increased neutrophils, increased monocytes)

Liver enzymes (increased alkaline phosphate)

Clinical signs of hyperadrenocorticism

Fat pads

Dehydration

PUPD

Abnormal bruising/poor healing

Muscle wasting & weakness

Depression

Hyperadrenocorticism causes

Adrenal Tumour

increased cortisol —> decreased ACTH

shrinks unaffected adrenal gland

Pituitary Tumour

ACTH & cortisol increased —> too much cortisol leads to dehydration

doesn't respond to -ve feedback

ACTH stimulation test

Synthetic ACTH injection
Stimulates ACTH levels to increase in healthy animal
Won't increase in dog with Cushing's

Dexamethasone suppression test

Injection of dexamethasone (glucocorticoid steroid)
Levels of cortisol should be suppressed (decreased) in a healthy animal
Increase if -ve feedback not working

slight suppression means hypoadrenocorticism likely

Treating Hyperadrenocorticism

- Adrenal steroid synthesis inhibitors (trilostane)
- Dopamine receptor agonists (only horses)

Adverse effects of using trilostane

- Hypoadrenocorticism (can be fatal)
- Electrolyte abnormalities (can be fatal)
- Inhibits progesterone (don’t use in pregnant animals)

Dopamine receptor agonists cause the overproduction of ___ and are used to treat ___ in horses

ACTH

Pituitary Pars Intermedia Dysfunction (PPID)

caused by loss of dopaminergic inhibition to intermediate lobe of pituitary

'equine cushings' = old terminology

Hypoadrenocorticism is also known as ....

Addison's disease

What causes hypoadrenocorticism

Autoimmune disease or sudden withdrawal of corticosteroid therapy

body attacks & destroys the cortex of the adrenal glands

disrupts metabolism, blood pressure regulation, fluid & electrolyte balance, & stress response

Testing for hypoadrenocorticism

Serum electrolytes —> (decreased calcium & chloride, increased potassium)

Serum biochemistry —> (decreased glucose & cholesterol)

Haematology —> (increased lymphocytes)

How can hypoadrenocorticism be treated?

Replacement therapy of glucocorticoids and/or mineralocorticoids

Adverse effects of corticosteroids

Cushing's syndrome (in overdose)
GI ulceration
Hyperglycaemia
Laminitis
Muscle wastage

Wound healing impaired & opportunistic infections can occur

Osteoporosis

Fluids & electrolyte imbalances

Reduced milk yield in dairy cows

Abortion in late pregnancy