Thyroid Flashcards
What is TSH and what does it do?
Thyroid-stimulating hormone
Thyrotropin
Glycoproteins produced by the anterior pituitary
Stimulates the thyroid gland
What does the thyroid gland produce
Mainly T4 some T3
T3 is 5 fold more active than T4
T4 is activated in the peripheries
How is T3 and 4 transported in the blood
Most is bound in the plasma to thyroxine binding globulin
The unbound portion is the active part
What are the action of T3 and 4
Inc cell metabolism
Via nuclear receptors
Vital for growth and mental development
They also inc catecholamine affects
What are thyroid hormone abnormalities caused by
Usually due to problems in the thyroid itself rarely problems in the hypothalamus or pituitary
Basic thyroid hormone tests
Free T3&4
Not total because this is affected by TBG when TBG in so will Total T3&4
When is TBG increased
Pregnancy, oestrogen therapy HRT COCP and hepatitis
When is TBG dec
Nephrotic syndrome - protein loss Malnutrition - protein loss Drugs- corticosteroids, phenytoin Chronic liver disease Acromegaly
What tests to order when hyperthyroidism in suspected
Ask for T3 T4 and TSH
All types have dec TSH except for rare pit secreting adenoma most have raised T4
What tests to order when hypo thyroid suspected
Only T4 and TSH
T3 no extra info
Sh varies through the day so try to do it at the same time each day
What is sick euthyroid
Any systemic illness TFTs mayb become deranged
Typical pattern is everything low
Tests should be repeated after recovery
Other tests to do in thyroid
Thyroid autoab TSH receptor Ab Serum thyroglobulin US Isotope scan
What autoantibodies to do
TPO - Antithyroid Peroxidase
Antithroglobulin ab
What is associated with which ab
TPO - hashimotos
antithyroglobulin - graves or hashimoto
TSH receptors Ab inc graves
Hat is useful in the tx of carcinoma monitoring
Serum thyroglobulin
What is an USS scan used for
This distinguishes cystic (usually but not alway benign) from solid (usually malignant) nodules
Can then take FNA from the nodules to determine if it is cancerous and what types of cancer
Types of thyroid cancer
Follicular Medullary - c cells so may produce calcitonin may be a part of MEN 2 syndrome - need to perform a phaeochromocytoma screen Anaplastic Papillary - most common Lymphoma
What is an isotope scan used for
Iodine or technetium pertechnetate
Useful for determining cause of hyper thyroidism & to detect a retrosternal goitre, ectopic thyroid tissue or thyroid mets (+whole body CT)
If there are suspicious nodules the question is are they hot or cold
Isotope scan hot nodule what does it mean
Increased up take is a hot nodule and these aren’t typically malignant
What does a neutral nodule mean on an isotope scan
Doesn’t take up anymore radio isotope than any other area on the thyroid
These aren’t typically malignant
What does a cold area mean on an isotope scan of the thyroid
The area takes up less radio isotope than the rest of the thyroid
20% of cold nodules are malignant
When is surgery most likely needed on thyroid nodules
Rapid growth Compression signs Dominant nodule on scintigraphy - dominant nodule on reader of the isotope Nodule same or bigger than 3cm Hypo-echoenicity
What abnormalities should be screened for those with thyroid dysfunction
AF Hyperlipidaemia DM T1DM in1st trimester and post delivery Patients on amioderone or lithium Patients with Downs or Turners Syndrome Addison’s disease
What does inc TSH and low T4 mean
Hypothyroidism
What is inc TSH and normal T4
Patient doesn’t regularly take their replacement medication
Or subclinical hypothyroidism
Inc TSH and inc T4
TSH secreting tumour or thyroid hormone resistance
Inc TSH and inc T4 and dec T3
Slow conversion to the active form T4 to T3
Deiodinase deficiency, euthyroid hyperthyroxaemia
Thyroid hormone antibody artefact
Dec TSH inc T4 and inc T3
Hyperthyroidism
Dec TSH and normal T4 and T3
Subclinical hyperthyroidism
Dec TSH and dec T4
Central hypothyroidism (hypothalamic or pituitary disorder )
Dec TSH dec T4 and T3
Sick euthyroid
Pituitary disease
Normal TSH abnormal T4
Consider changes in the thyroid-binding globulin, assay interference, amioderone, pituitary TSH tumour
What is thyrotoxicosis
Excess thyroid hormone usually from gland hyperfunction
Symptom of thyrotoxicosis
Diarrhoea Dec weight Inc appetite Can get paradoxical weight gain in 10% Over active Sweats Heat intolerance Palpitations Tremor Irritability Labile emotions Oligomenorrhoea \+/- infertility Rare psychosis, chorea, panic, itch , alopecia, urticaria
Signs of thyrotoxicosis
Inc HR/irregular - AF, SVT, rare VT Warm moist skin Fine tremor Palmar erythema Thin hair Lid lag Lid retraction Potential goitre
Signs of Graves’ disease
Eye disease - exophthalmos, proptosis, conjunctival oedema, corneal ulceration, papilloedema, loss of colour vision.
Pretibial myxoedema - swelling above the lateral malleoli
Thyroid acropatchy - clubbing, periosteal action in limb bones
Test results in hyperthyroidism
Inc T4 and T3 Dec TSH May be mild normocytic anaemia Mild neutropenia Inc ESR Inc ca2+ Inc LFT Check thyroid autoantibodies If cause unclear may want isotope scan Eye disease - ophthalmoscope , visual fields, acuity, eye movements.
What are the causes of thyrotoxicosis
Graves’ disease Toxic multinodular goitre Toxic adenoma Ectopic thyroid gland tissue Exogenous
What is the most common cause of hyperthyroidism
Graves’ disease
What is the prevalence and cause of Graves’ disease
More common in women age 40-60
Cause circulating IgG autoantibodies binding to & activating G-protein coupled thyrotropin receptors which are smooth thyroid enlargement and hormone production particularly T3 and react to orbital autoantigens
Triggers of Graves’ disease
Stress
Infection
Childbirth
Are patients always hyperthyroid in graves
Most hyper but can be eu and hypo
Is graves associated with autoimmune diseases
Yes
Vitiligo
T1DM
Addisons
Who gets toxic nodular goitre
Elderly
Iodine deficient areas
What does a toxic multi nodular goitre do
Nodules secrete hormones
Tx of toxic multinodular goitre
Tx same as graves
If compressive surgery is indicated
- dysphagia or dyspnoea
What is a toxic adenoma
Solitary nodule producing T3 and T4
On isotope scan hot nodule
And the rest of the gland is suppressed
What is ectopic thyroid tissue
Metastatic follicular thyroid cancer
Struma overii -ovarian teratoma with thyroid tissue
What is subacute de quervains thyroiditis
Self limiting post viral with painful goitre inc temperature +/- inc ESR
Tx NSAIDs
Tx hyperthyroidism
Drugs
Beta blockers - propranolol control rapid symptoms
Treat the condition - these drugs are used to decrease thyroid hormone synthesis by acting as a preferred substrate or iodisation by thyroid peroxidase the key enzyme in thyroid hormone synthesis
- carbimazole and propyluracil
2 regimens for carbimazole - titrate it up and give carbimazole and Levothyroxine at the same time
Prpyluracil is a second line due to the small chance of liver toxicity
Surgical - radioiodine tablet
Hasn’t been shown to inc risk of cancer Roth defects or infertility in women
CI in pregnancy , lactating and you need to be kept further away from children when you have the tx
Thyroidectmy usually total risk = damage to recurrent laryngeal nerve = hoarseness and lack of voice
Radioidione and thyroidectomy - become hypothyroid so need replacement but is better than potential longterm effects of being hyper and the medication se
Complications of hyperthyroidism
Heart failure - thyrotoxicosis cardiomyopathy Angina AF Osteoporosis Ophthalmology Gynacomastia Thyroid storm
What causes thyroid eye disease
Retro orbital inflammation and lymphocyte infiltration resulting in swelling of the orbit
What is the main risk factor for thyroid eye disease
Smoking
Prevalence of thyroid eye disease
25-50% of those with Graves’ disease
Does the eye disease correlate with thyroid disease
May not
The patient could be euthyroid, hypo or hyper
How does thyroid eye disease present
It was be the first presenting feature of graves
And can be worsened by tx typically radioiodine but is typically transient
Symptoms of thyroid eye disease
Eye discomfort Grittiness Inc tear production Photophobia diplopia Dec acuity RAPD - may mean optic nerve compression, depression may be needed get help at once
Does eye protrusion mean nerve damage
No
If the eye cannot protrude more likely to lead to optic nerve compression
Signs of eye disease
Exophthalmos - appearance of protruding eye
Proptosis - eye protrude beyond the orbit
Conjunctival oedema
Corneal ulceration
Papilloedema
Loss of colour vision
Ophthalmoplegia
Test for thyroid eye disease
The diagnosis is clinical so none needed
A ct/mri would show enlarged eye muscles
Mx of thyroid eye disease
Con - stop smoking
Med - symptoms: artificial tears, sunglasses, avoid dust
Diplopia - fresnel prism on lens
More severe may need high dose steroids
Surg - surgical decompression in severe sight threatening conditions eye lid surgery for cosmesis & function
Orbital radiotherapy - used to treat ophthalmoplegia
Future: anti TNF alpha antibodies - infliximab
Causes of goitre
Physiological
Graves’ disease
Hasimotos thyroiditis
Subacute (de Quervain’s thyroiditis) - painful
What is the first line treatment in toxic nodular goitre
Radioiodine
What happens in the pituitary in Graves’ disease
TSH is suppressed
And the expression of thyrotropin beta subunit
What happens to the heart in Graves’ disease
Inc rate
Inc contractility
Inc serum atrial beta natriuretic peptide
What is hypothyroidism
Clinical affect of a lack of thyroid hormone
Symptoms of hypothyroidism
Tiredness, sleepy, lethargic, dec mode, cold-disliking,inc weight, constipation, menorrhagia, hoarse voice, dec memory and cognition, myalgia, cramps, weakness
Signs of hypothyroidism
BRADYCARDIA R = reflexes slow A = ataxia D = dry/thin skin Y = yawning/ tired C = cold hands A = ascites R= round puffy face/double chin D= demeanour - low I = immobile C=CCF
Diagnosis of hypothyroidism
TFTs
Low T4/3
High TSH
Rare secondary from pituitary both low
Causes of primary autoimmune hypothyroidism
Primary atrophic hypothyroidism = diffuse lymphocytic infiltration of the thyroid, leading to atrophy, no goitre
Hashimoto’s thyroiditis = goitre due to lymphocytic and plasma cell infiltration, ab TPO antithyroglobulin high
Worldwide = iodine deficiency
Post thyroid radioiodine tx or thyroidectomy
Drug induced - amioderone, lithium
Associations with hypothyroidism
Other autoimmune conditions
- Addison’s, T1DM, pernicious anaemia
- turners and Down’s syndrome, CF, PBC, ovarian hyper stimulation, POEMS syndrome - poyneuropathy, organomegaly, endocrinopathy, m-protein band (plasmacytoma)+ skin pigmentation/tethering
Problems in pregnancy in hypothyroidism
Eclampsia Anaemia Prematurity Low birthweight Stillbirth PPH
Tx hypothyroidism
Young give Levothyroxine and titrate to clinical picture
Elderly give 25 to start and adjust accordingly
What does amioderone do to the thyroid gland
It is an iodine rich drug
Structural like T4
Hypothyroidism as T4 can be inhibited due to iodine excess
Hyperthyroidism can be caused by toxic thyrotoxicosis which causes hormone release
Check tft monthly on amioderone
If cannot stop amioderone then a thyroidectomy may be needed
What is the state before death in hypothyroidism
Myxoedema coma
What is subclinical hypothyroidism
TSH >4
Normal T4 and T3 no symptoms
Small risk of progression to hypothyroidism
This inc the higher the TSH, male, and if you have TPO ab
May need treating see if they get any better
What Is subclinical hyperthyroidism
TSH low
Normal T4/T3
Rule out rare secondary hyperthyroidism - central cause, pregnancy, illness
