Thyroid disorders Flashcards
Where is the thyroid gland located?
Between C5-T1
What are the two lobes of the thyroid connected by?
The isthmus
What important structures are located close to the thyroid gland and must be considered when operating on the thyroid gland?
- Recurrent laryngeal nerve
- Superior laryngeal nerve
- Parathyroid glands
- Trachea
- Common carotid artery
- Internal jugular vein
What is T3 also known as?
Triiodothyronine
What is T4 also known as?
Thyroxine
Which of T3 and T4 is more active and which is produced more?
T3 is more active but more of T4 is released
What is the thyroid gland made up of?
Lots of follicles consisting of follicular cells surrounding a protein-rich material called the colloid
What does synthesis of T3 and T4 begin with?
Circulating iodine being actively transported with Na+ ions across the basolateral membrane of the follicular cells
Once inside the follicular callow does iodide cause T3/4 synthesis?
- Oxidised to iodine
- Iodine bind to tyrosine on thyroglobulin molecules
- If tyrosine binds to one iodine = T1, If bind to two = T2
- Thyroid gland is stimulated and the T1 and T2 molecules are cleaved from tyrosine and join to either make T3 or T4
- Follicular cells engulf the T3 and T4 containing portions of the colloid via endocytosis
- TSH stimulates movement of Colliod into secretory cells
- Proteolysis results in T3 and T4 release
How much iodinated thyroglobulin is stored in follicles?
Enough to provide thyroid hormone for several weeks even in the absence of dietary iodine
What is graves disease?
- Cause of hyperthyroidism
- Autoimmune condition that results in excess secretion of thyroid hormones and hyperplasia of thyroid follicular cells
What is a toxic multinodular goitre?
- Cause by a lack of dietary iodine
- The anterior pituitary compensates by producing more TSH leading to thyroid hypertrophy and hyperplasia
What is de quervain’s thyroiditis?
- Transient hyperthyroidism which sometimes results from acute inflammation of the thyroid gland
What drug can induce hyperthyroidism?
Amiodarone - an anti-arrhythmic drug that can cause both hypo and hyperthyroidism
What risk factors are associated with hyperthyroidism?
- Female
- Genetic
- Autoimmune disease
- Smoking
- Stress
What three effects does graves disease have?
- Hyperthyroid effects
- Opthamological effects
- Dermatological
What are the general signs of hyperthyroidism?
- Hands - palmar erythema
- Diffuse goitre
- Lid lag and stare
- Hyperkinesis
- Warm
Proximal myopathy and muscle wasting
What are the symptoms of hyperthyroidism?
- Palpitations
- Diarrhoea
- Weight loss and increased appetite (due to higher metabolic rate)
- Oligomenorrhea +/- infertility
- Heat intolerance
- Irritability/behavioural change
- Anxiety
What would you see on a thyroid function test in hyperthyroidism?
TSH is low and T3 and T4 are raised
If there was a secondary cause of hyperthyroid what would be different about the TFTs?
TSH will be elevated as the problem is with the pituitary
What imaging technique can be used in detection of thyroid disorders?
Ultrasound
What other test can you do in thyroid disorders?
- Thyroid peroxidase (TPO) and thyroglobulin antibodies which are found in hyperthyroidism
What is the main complication of hyperthyroidism?
Thyroid crisis where the effects of excess thyroid hormone is magnified.
- Heat intolerance turns into fever
- Rapid heart rate turns into arrhythmias
How is thyroid crisis treated?
Large doses of
- Carbimazole
- Propranolol
- Potassium iodide (to block acutely the release of thyroid hormone from the gland)
- IV hydrocortisone (inhibits conversion of T4 to T3)
What is the specific treatment used in graves?
- IV methylprednisolone and surgical decompression
What pharmacological treatments can be used in hyperthyroidism?
- Beta blockers (propranolol)
- Antithyroid drugs (carbimazole)
- Radioactive iodine
- Surgical if large goitre of poor response to drugs
What is hypothyroidism?
Under activity of the thyroid gland which can be due to a primary or a secondary cause
What is the most common cause of hypothyroiditis?
Autoimmune
What happens in autoimmune hypothyroiditis?
Antithyroid antibodies lead to atrophy and fibrosis of the gland
What is hashimoto’s thyroiditis?
- Autoimmune condition where there is atrophy of the thyroid gland but then regeneration that results in a goitre formation
What is postpartum thyroiditis?
A transient form of hypothyroidism that is observed following pregnancy - usually found in those that have an underlying mild autoimmune condition
What does an iatrogenic cause mean?
A cause due to a treatment or examination e.g thyroidectomy
What drugs can induce hypothyroidism?
- Carbimazole
- Lithium
- Amiodarone
What deficiency can cause hypothyroidism?
Iodine deficiency
What are the risk factors of hypothyroidism?
- Autoimmune hypothyroidism associated with other autoimmune diseases
What are the signs of hypothyroidism?
- Bradycardia
- Slow reflexes
- Ataxia
- Dry thin hair and skin
- Yawning
- cold hands
- Ascites
- Round puffy face
- Defeared demeanour
- Immobile
- Congestive cardiac failure
What are the symptoms are hypothyroidism?
- Hoarse voice
- Goitre
- Constipation
- Cold intolerance
- Weight gain
- Menorrhagia
- Myxoedema
- Myalgia
- Tired, low mood, dementia
What would you see on the Thyroid function tests in hypothyroidism?
- TSH is high
- T3/4 are low
What might a blood test show in hypothyroidism?
- Anaemia
- Raised AST’s
- Increased serum creatinine kinase
- Hypercholesterolaemia
- Hyponatraemia
What is the treatment for hypothyroidism?
- Lifelong thyroid hormone replacement e.g oral levothyroxine
What are the five types of thyroid carcinoma?
- Papillary
- Follicular
- Anaplastic
- Lymphoma
- Medullary cell
What are the features of a papillary tumour?
- Most common
- Well differentiated
- Young people
- Local Spread and good prognosis
- Arises from thyroid epithelium
What are the features of a follicular tumour?
- Well differentiated
- Middle age
- Spread to lung/bone usually good prognosis
- Arise from thyroid epithelium
What are the features of an anapaestic tumour?
- Very undifferentiated and arise from thyroid epithelium
- Aggressive, local spread but poor prognosis
What are the features of a medullary cells tumour?
- Arise from calcitonin C cells of the thyroid gland
What is the presentation of a thyroid carcinoma?
- Thyroid nodule is present in 90% of cases
- Cervical Lymphadenopathy
- If thyroid gland increases in size, it becomes hard and is an irregular shape
What investigations would you perform in a suspected thyroid carcinoma?
- Fine needle aspiration cytology biopsy - used to distinguish between benign or malignant nodules
- TFTs - to check for hyper/hypo
- Ultrasounds of thyroid
What is the treatment for a thyroid carcinoma?
Radioactive iodine effective as the thyroid loves iodine so takes it up and will destroy the cancer providing little damage to surrounding structures
Which type of thyroid carcinoma does not respond to radioactive iodine?
Anaplastic
Why should levothyroxine by administered alongside other treatments?
To keep TSH levels reduced as this is a growth factor for the cancer
What can chemo be used for?
To help reduce the risk of spread and treats micro-metastases
