Hyper/Hypo - Thyroidism Flashcards
Where is TSH produced?
Anterior pituitary
How does T3 and T4 travel in the blood?
In the plasma bound to a protein, TBG
What is the structure of the thyroid gland?
Lies against and around front larynx and trachea, below thyroid cartilage
What is the majority of the thyroid hormone circulating in the blood?
T4
What protein is needed to make T3 and T4?
Tyrosine
What mineral is needed to make thyroid?
Iodine
Where is TRH produced?
Hypothalamus
Where are the receptors for T3 and T4?
In the nuclei of cells
What is the action of thyroid hormones?
- Increased BMR and heat production
Lipid metabolism - Lipolysis and beta oxidation
Carbohydrate metabolism - Stimulates insulin dependent entry of glucose into cells, increasing gluconeogenesis and glycogenolysis
Sympathomimetic - Increases response to catecholamines by increasing receptor number on target cells
What is the effect of thyroid hormone on the CVS?
- Increases heart response to catecholamines
- Increases CO by increasing HR and force of contraction
What is the effect of thyroid hormone on peripheral vasculature?
- Vasodilation to carry heat to body surface
What is the effect of thyroid hormone on the nervous system?
- Myelination of nerves
- Development of neurones
What thyroid function tests should you ask for if you suspect hyperthyroidism?
- T3 and T4
- TSH (all will have low TSH apart from TSH secreting pituitary adenoma)
What thyroid function tests should you ask for if you suspect hypothyroidism?
- T4
- TSH
T3 will not add any extra information
What is sick euthyroidism?
- TFT’s become deranged with systemic illness
What is TPOAbs? What is it testing?
TPOAbs - Thyroid peroxidase antibodies
- Increased in hypothyroid autoimmune thyroid disease
- If positive in Grave’s, there is an increased chance of developing hypothyroidism later on
What does TSH receptor antibody test for?
- Grave’s disease, raised
- Useful in pregnancy
What does serum thyroglobulin test for?
- Treatment of carcinoma
- Detection of self medicated hyperthyroidism if thyroglobulin is low
What is the use of ultrasound in thyroid disease?
- Can distinguish between cystic benign nodules and solid malignant nodules
When is a fine needle aspiration indicated?
- A solitary nodule
- Multinodular goitre
What is the use of an isotope scan?
- Useful to determine the cause of hyperthyroidism
- Finds retrosternal goitre
- Finds ectopic thyroid tissue
- Finds thyroid metastases with whole body CT
What patients should you screen for thyroid abnormalities?
- AF
- Hyperlipidaemia (hypothyroidism)
- Women with type I DM during 1st trimester and post delivery
- Amiodarone or lithium (biannually)
- Downs syndrome, Turners syndrome, Addisons disease (annually)
What are the symptoms of hyperthyroidism?
- Diarrhoea
- Weight loss
- Increased appetite (paradoxical weight gain in 10%)
- Overactive
- Sweats
- Heat intolerance
- Palpitations
- Tremor
- Irritability
- Labile emotions
- Oligomennorrhoea +/- infertility
What are the signs of hyperthyroidism?
- Pulse fast/irregular - AF/SVT
- Warm moist skin
- Fine tremor
- Palmar erythema
- Thin hair
- Lid lag
- Lid retraction
- Goitre
- Thyroid nodules
- Thyroid bruit
What are some specific signs of grave’s disease?
Eye disease - exopthalmous, ophthalmoplegia
Pretibial myxoedema - Oedematous swellings above lateral malleoli
Thyroid acropachy - Clubbing, painful finger and toe swelling, periosteal reaction in limb bones
What investigations would you undertake in suspected hyperthyroidism?
You want to distinguish between thyrotoxicosis and actual hyperthyroidism
Bloods -
- TSH, T3, T4
- TSH receptor antibodies (TRAbs) diagnoses Grave’s
Isotope scanning -
- If TRAbs are negative
- Thyroiditis will have low uptake on thyroid scan, actual hyperthyroidism will have high uptake
Ultrasound -
- Only if palpable nodule
- From this, decide if to do FNA
Visual assessment -
- Visual acuity and visual fields
What are the causes of hyperthyroidism?
- Grave’s disease
- Toxic multinodular goitre
- Toxic adenoma
- Ectopic thyroid tissue
- Exogenous - Iodine excess - contamination, contrast, levothyroxine
- Subacute de Quervain’s thyroiditis
- Amiodarone, lithium
- Postpartum
- TB
What is the cause of Grave’s disease?
- Circulating IgG autoantibodies binds to and activates GPCR of thyroglobulin
- Causes smooth thyroid enlargement and increased hormone production (esp T3)
What triggers Grave’s disease?
- Stress
- Infection
- Childbirth
What is Grave’s associated with?
Other autoimmune diseases
- Vitiligo
- Addison’s
- Type 1 DM
What is toxic multinodular goitre?
Where is it common?
When is surgery indicated?
Nodules secrete thyroid hormones.
- Seen in the elderly and in iodine deficient areas
- Surgery is indicated when there are compressive symptoms of the goitre (dysphagia, dyspnoea)
What is toxic adenoma?
How can you differentiate this from malignancy?
A solitary nodule that produces T3 and T4.
On a radioisotope scan the nodule is ‘hot’ and the rest of the gland is suppressed.
Where can ectopic thyroid tissue be found?
- Metastatic follicular thyroid cancer
- Ovarian teratoma with thyroid tissue (struma ovarii)
What is subacute de Quervain’s thyroiditis?
What would make you think this?
What is the treatment?
- Self limiting post viral with a painful goitre
- Increased temperature and raised ESR
- Low isotope uptake on scan
- Treat with NSAID’s, and symptomatic treatment with beta blockers
What is the treatment for hyperthyroidism?
- Beta blockers - Controls symptoms
- Anti thyroid medication
- Titration with carbimazole, reduce according to TFT’s every 1-2 months
- Block and replace aka give carbimazole and levothyroxine simultaneously. Less risk of iatrogenic hypothyroidism.
- Need FBC and LFT’s before they start - Radioactive iodine - Most become hypothyroid post treatment. Cant be used in pregnancy/lactation.
- Thyroidectomy - Risk of recurrent laryngeal nerve damage (hoarse voice) and hypoparathyroidism. Thyroid replacement needed.
- Seek expert help in pregnancy and infancy.
What are the side effects of carbimazole?
What should you warn a patient about?
- Agranulocytosis (low neutrophils) so risk of dangerous sepsis
- Stop if they get signs of infections and get a FBC urgently (eg fever, mouth ulcers, sore throat)
What are the complications of hyperthyroidism?
- Heart failure (toxic cardiomyopathy)
- Angina
- AF
- Osteoporosis
- Opthalmopathy
- Gynaecomastia
- Thyroid storm
What are the symptoms of hypothyroidism?
- Tiredness
- Sleepy
- Low mood
- Cold disliking
- Weight gain
- Constipation
- Menorrhagia
- Hoarse voice
- Memory loss and cognition impairment
- Dementia
- Myalgia
- Cramps
- Weakness
What are the signs of hypothyroidism?
BRADYCARDIC
B - Bradycardia R - Reflexes relax slowly A - Ataxia (cerebellar) D - Dry thin hair/skin Y - Yawning/drowsy/coma C - Cold hands and low temperature A - Ascites and non pitting peripheral oedema R - Round puffy face/double chin/obese D - Defeated demeanour I - Immobile or ileus C - CCF
What are the blood results for hypothyroidism?
- Raised TSH (over 4mu/L) (low in rare secondary hypothyroidism)
- Low T4
- Increased cholesterol and triglyceride
- Macrocytic anaemia
What are the 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 lymphocytes and plasma cell infiltration. Commoner in women 60-70.
What are the non autoimmune causes of primary hypothyroidism?
- Iodine deficiency
- Post thyroidectomy/radioiodine treatment
- Drug induced - antithyroid, amiodarone, lithium, iodine
- Subacute thyroiditis - temporary after hyperthyroid phase
What is the cause of secondary hypothyroidism?
- Not enough TSH due to hypopituitarism (very rare)
What is autoimmune hypothyroidism associated with?
- Other autoimmune conditions
- Turner’s and Downs syndrome
- Primary biliary cholangitis
- Cystic fibrosis
What is the risks of pregnancy with hypothyroidism?
- Eclampsia
- Anaemia
- Prematurity
- Low birthweight
- Stillbirth
- PPH
What is the treatment for hypothyroidism?
Healthy and young -
- Levothyroxine - Ensure TSH is not suppressed
- Check TSH every 2-3 months, then check TSH yearly once stabilised
- Council that it may take 6 months for TSH to go back to normal
Elderly/IHD -
- Use lower dose as may precipitate angina or MI
Why do problems occur with amiodarone?
How can it cause these problems?
What should you monitor?
- It is structurally like iodine
- Can cause hypo - toxicity from iodine excess, inhibiting T4
- Can cause hyper - Destructive thyroiditis
Check TFT’s biannually and thyroidectomy if amiodarone cannot be stopped
