Thyroid Flashcards by alice Sawka

Use of TPO antibodies

suspected hashimotos thyroiditis
not usually needed for diagnosis
has predictive value for determining risk of development of overt hypothyroidism
Postpartum thyroiditis occurs in 30% of women with elevated levels.

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TSH receptor antibody use

graves disease but not usually needed for diagnosis- usually would use radioiodide uptake unless contraindicated ie pregnant

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Clinical use of serum thyroglobulin

suspected subacute thyroiditis or suspect surreptitious ingestion of thyroxine
Can be used as tumour marker in people with well differentiated thyroid cancer.
Remember that difficult to interpret when thyroglobulin antibodies

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Why do you not measure T3 in hypothyroidism?

Because T3 levels are often conserved even if there is signifiant hypothyroidism

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Increased anti TPO ab and anti thyroglobulin antibodies think…

Hashimotos

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Elevated thyroid stimulating immunoglobulins and thyrotropin binding inhibitory immunoglobulins (TBIIs) think….

Graves

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What could you measure in a patient with a family history of autoimmune hypothyroidism to determine future risk:

anti-TPO ab (NOT anti-thyroglobulin Ab) - but no value for serial measurement unless wanting to get pregnant (higher risk preterm delivery, miscarriage, infertility)

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why measure serum thyroglobulin?

Low levels in serruptitious thyroxine
High levels in hyperthyroidism and thyroid destruction
Tumour marker for well differentiated papillary or follicular ca
Need to measure serum thyroglobulin ab at same time- if ab present then level of thyroglobulin not a reliable test

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Why measure serum calcitonin

Secreted from C cells in thyroid gland
Tumour marker in medullary Ca
Don’t measure in everyone with a thyroid nodule, but should measure if FB thyroid Ca, features of MEN2, or biopsy shows medullary

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Causes of thyrotoxicosis

Grave's
TMNG
Toxic adenoma
TSH secreting pituitary adenoma
Exogenous T4/T3
Iodine load- Jod-Basedow
Lingual thyroid
Amiodarone
Thyroiditis- acute/subacute/postpartum/silent/Hashimoto/Drug induced/Traumatic/Riedel/radiation
hCG mediated- gestational thyrotoxicosis- usually with hyperplacentosis- molar preg or multiple preg

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If TSH is high/normal with high T3 or 4 and suspect TSH secreting tumour, then can do a…

alpha subunit to serum TSH ratio which will be more than one if tumour is source

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When to chose methimazole

Most cases as better side effect profile (hepatic)

NOT in pregnancy-teratogenic

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When to choose propylthiouracil

First trimester of pregnancy.

Worse side effects- mainly hepatic

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MEchanism of action of methimazole

Inhibits TPO–>no conversion of iodide to iodine which facilitates attachment to thyroglobulin

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Methimazole and propylthiouracil can cause…

agranulocytosis
LFT derangements
drug rash in 5-10 percent

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Why should you avoid thyroid ablation in graves ophthalmopathy?

Can worsen at least transiently

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Graves ophthalmopathy signs

lid retraction
chemosis
lid lag
cannot close eyes completely (lagophthalmos)
widened palpebral fissure
eye globe lag on supraduction
epithelial errosions
inferior rectus myopathy–>vertical diplopia
optic nerve damage–>emergency, blindness

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Jod-Basedow phenomenon

Where an iodine load from contrast induces thyrotoxicosis in a patient who already has a degree of autonomy from TSH due to activating somatic mutation in receptor

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Graves disease features

Generic features of thyrotoxicosis
Thyroid ophthalmopathy
Pre-tibial myxoedema
Thyroid acropachy
Goitre with anatomical enlargement

Thyrotoxicosis any cause

Anxiety
Tremor
Weight loss
Sweating
Increased appetite
Heat intolerance
Diarrheoa
oligomenorrhoea
weakness
palpitations
dyspnoea/chest pain/reduced exercise tolerance

Decreased visual acuity in graves what mechanism?

Pressure on optic nerve from oedema

Complications of Grave’s diseas

Myopathy
Psychosis
Hypokalaemic periodic paralysis, associated myasthenia
AF, high embolic risk
Heart failure
Osteoporosis
Pigmentation, thin skin, onycholysis
neutropenia, lymphocytosis, thrombocytopaenia

In Graves, when would you be more likely to start antithyroid drug? (as opposed to radiation or surgery)

Pregnant- but second trimester uncontrolled thyrotox use surgery. ALSO CARBIMAZOLE CAUSES FETAL SYNDROME BEFORE 12 weeks.
Patients less than 40
small goitre
low titre thyroid antibodies

In old patients, males, large goitre, large titre TRAB, unlikely to spontaneously remit and so ablative therapy may be more appropriate

When to avoid radioiodide treatment for Graves

Large goitre- may only reduce slightly
May exacerbate graves ophthal- can give steroids to try and protect
Dont use in pregnancy and only cautiously in patients of reproductive age

Carbimazole counselling

Idiosyncratic agranulocytosis in 0.4% - idiosyncratic and no point in monitoring- stop takind drug if unexplained febrile, mouth ulcers, sore throat. Carbimazole and propythiouracil 10% risk rash Propylthiouracil rare fatal hepatotoxicity so not first line

Why are thionamides nor as good in TA or MNG?

due to a constitutive mutation and spontaneous remission unlikely. Probably won't induce remission with drugs

When to treat subclinical hyperthyroidism- sub normal TSH with normal T3 and T4

1-2% risk progression to overt disease per year, more if MNG if TSH less than 0.1- risk of progression, AF, CCF, ostroporosis Treat if existing heart disease or osteoporosis, MNG

Hypothyroidism features

``` Cold Fatigue/lethargy Reduced appetite menorrhagia weight gain thin hair loss dry coarse skin oedema memory loss depression and anxiety thick tongue slow speech constipation ```

By what proportion do you need to pre-emptively increase thyroxine in pregnancy

50% v

Subclinical hypothyroidism (raised TSH in setting of normal T3 and T4)

natural progression to hyothyroidism 2.5% per year, all need to be followed up, higher risk if antibodies present Treat to prevent hypothyroidism if TSH over 10 no evidence of benefit (symptoms do not improve in studies) if TSH less than 10 Also treat if TSH over 2.5 and pregnant or thinking about being pregnant Treat if Under 65 If heart failure

Clinical features of De-Quervain's thyroiditis AKA subacute thyroiditis- VIRAL CAUSE

Painful, swollen thyroid, jaw pain, hoarse voice Constitutional symptoms, fever Thyrotoxicosis features Sx last 2-8 weeks

Tests in De-Quervain's AKA subacute thyroiditis- VIRAL

ESR and CRP up Thyroglobulin elevated isotope scan low or absent uptake USS large hypoechoic gland with reduced vascularity

Treatment of subacute thyroiditis

``` NSAID/aspirin if mild pred 40mg then taper otherwise propanolol or metoprolol for sx thionamides INEFFECTIVE thyroxine in hypothyroid phase ```

Outcome in subacute thyroiditis

90% resolve, 10% stay hypothyroid | can have recurrent episodes

Lymphocytic and post partum thyroiditis clinical features

``` painless enlargement of thyroid gland + thyrotoxicosis low echogenicity on USS low uptake on scan high thyroglobulin aTPO and TG antibodies bx lymphocytic infiltration common presentation post partum thyrotoxicosis-->hypothy-->20-30% persisting hypothyroid antithyroid drugs NOT useful ```

What is Riedel's thyroiditis

Fixed painless mass + eu/hypothyroidism Dense fibrosis extending to adjacent structures, associated Hornders, carotid stenosis, hypoparathyroidism probably on the spectrum of IgG4 disease Tx surgery, steroids, mycophenolate, tamoxifen

bad nodule features on USS

hypoecoic, microcalcification, taller than wide, irregular margins, broken egg shell rim IF not a HOT nodule on isotope uptake and over 2cm then biopsy, if 1-2 cm then decide based on USS features if under 1cm then do in 6-12 months USS- if increase 30% on USS in volume or 10% diameter -->bx

when to treat subclinical hyperthyroidism?

AF Osteoporosis Symptoms TSH under 0.1

Types of amiodarone induced thyroid disorder-

Hypothyroidism due to Wolff-Chaikoff effect (saturated NI symporter due to iodine load from amiodarone) Hyperthyroidism 1. type 1 from Jod Basedow iodine load -treat with carbimazole or PTU 2. Type 2 from thyroiditis and hormone release- replace with steroids

Lithium effect on thyroid gland

Li inhibits T4 production and secretion -->hypothyroidism | May also cause thyroiditis

Good features on ultrasound of lump?

``` Cyst simple spongiform Partially cystic Hyperechoic Solid, regular margin ```

Mutations in thyroid cancers?

Medullary- RET Follicular- PAX8/PPARgamma- very specific Papillary - BRAF most common

"normal" effect of amiodarone on thyroid

Blocks T4 to T3 conversion so usually see increase T4 and reduced T3 from baseline Usually see increase in TSH slightly usually see slight increase in rT3 After 3-6 months reach steady state and TSh normal, T4 ULN, T3 low normal

Lithium causes what type of thyroid trouble?

More commonly hypothyroidism | Also hyperthyroidism

Hashimotos associated with which cancer?

Primary thyroid lymphoma Rapidly enlarging goitre, firm, with fever