HPT Flashcards
TSH and T3/T4 in hyperthyroidism
TSH is suppressed by high thyroid hormones resulting in low TSH
Exception is pituitary adenoma that secretes TSH in which case it is high
What is primary hyperthyroidism
Due to thyroid pathology producing excessive thyroid hormone
What is secondary hyperthyroidism
Thyroid is producing excessive thyroid hormone as a result of overstimulation by thyroid stimulating hormone.
The pathology is in the hypothalamus or pituitary.
What is grave’s disease
Autoimmune condition where TSH receptor antibodies cause a primary hyperthyroidism.
These TSH receptor antibodies are abnormal antibodies produced by the immune system that mimic TSH and stimulate the TSH receptors on the thyroid
What is the most common cause of hyperthyroidism
Grave’s disease
What is a toxic multinodular goitre
Condition where nodules develop on the thyroid gland that act independently of the normal feedback system and continuously produce excessive thyroid hormone.
What is exophthalmos
Term used to describe bulging of eyeball out of the socket caused by Graves Disease.
This is due to inflammation, swelling and hypertrophy of the tissue behind the eyeball that forces the eyeball forward.
What is pretibial myxoedema
Dermatological condition where there are deposits of mucin under the skin on the anterior aspect of the leg (the pre-tibial area). This gives a discoloured, waxy, oedematous appearance to the skin over this area.
What is pretibial myxoedema specific to
Specific to Grave’d disease and is a reaction to TSH receptor antibodies
Causes of hyperthyroidism
Grave’s disease
Toxic multinodular goitre
Solitary toxic thyroid nodule
Thyroiditis (e.g. De Quervain’s, Hashimoto’s, postpartum and drug-induced thyroiditis)
General features of hyperthyroidism
Anxiety and irritability Sweating and heat intolerance Tachycardia Weight loss Fatigue Frequent loose stools Sexual dysfunction
Features specific to Grave’s disease
Diffuse goitre (without nodules)
Graves eye disease
Bilateral exophthalmos
Pretibial myxoedema
Unique features of toxic multi nodular goitre
Goitre with firm nodules
Most patients are aged over 50
Second most common cause of thyrotoxicosis (after Grave’s)
What is a solitary toxic thyroid nodule and how are they managed normally
where a single abnormal thyroid nodule is acting alone to release thyroid hormone.
The nodules are usually benign adenomas. They are treated with surgical removal of the nodule.
What is de quervain’s thyroiditis
Presentation of a viral infection with fever, neck pain and tenderness, dysphagia and features of hyperthyroidism.
There is a hyperthyroid phase followed by a hypothyroid phase as the TSH level falls due to negative feedback.
Management of de quervain’s thyroiditis
Self-limiting condition and supportive treatment with NSAIDs for pain and inflammation and beta-blockers for symptomatic relief of hyperthyroidism is usually all that is necessary.
What is a thyroid storm
It is also known as “thyrotoxic crisis”. It is a more severe presentation of hyperthyroidism with pyrexia, tachycardia and delirium.
1st line anti-thyroid drug for hyperthyroidism
Carbimazole
2nd line anti-thyroid drug for hyperthyroidism
Propylthiouracil
Why is carbimazole preferred over propylthiouracil in hyperthyroidism
Small risk of severe hepatic reactions
How does radioactive iodine work in hyperthyroidism
This is taken up by the thyroid gland and the emitted radiation destroys a proportion of the thyroid cells. This reduction in functioning cells results in a decrease of thyroid hormone production and thus remission from the hyperthyroidism.
What do patients taking radioactive iodine as part of hyperthyroidism treatment require
Remission can take 6 months and patients can be left hypothyroid afterwards and require levothyroxine replacement.
Rules for patients taking radioactive iodine
Must not be pregnant and are not allowed to get pregnant within 6 months
Must avoid close contact with children and pregnant women for 3 weeks (depending on the dose)
Limit contact with anyone for several days after receiving the dose
Use of beta-blockers in hyperthyrodism
Block the adrenalin related symptoms of hyperthyroidism.
Propranolol is a good choice because it non-selectively blocks adrenergic activity
They do not actually treat the underlying problem but control the symptoms whilst the definitive treatment takes time to work. They are particularly useful in patients with thyroid storm.
Definitive management of hyperthyroidism
Surgically remove the whole thyroid or toxic nodules. This effectively stops the production of thyroid hormone, however the patient will be left hypothyroid post thyroidectomy and require levothyroxine replacement for life.
Most common cause of hypothyroidism in the developed world
Hashimoto’s thyroiditis
What is hashimoto’s thyroiditis
Caused by autoimmune inflammation of the thyroid gland. It is associated with antithyroid peroxidase (anti-TPO) antibodies and antithyroglobulin antibodies.
Initially it causes a goitre after which there is atrophy of the thyroid gland.
Most common cause of hypothyroidism in the developing world
Iodine deficiency
Medications which can cause hypothyroidism
Lithium
Amiodarone(usually causes hypothyroidism but can also cause thyrotoxicosis)
All of the pharmacological treatments for hyperthyroidism have the potential to cause hypothyroidism
What is secondary hypothyroidism
where the pituitary gland is failing to produce enough TSH. This is often associated with a lack of other pituitary hormones such as ACTH. This is called hypopituitarism
Causes of secondary hypothyroidism
Tumours
Infection
Vascular (e.g. Sheehan Syndrome)
Radiation
Presentation of hypothyroidism
Weight gain Fatigue Dry skin Coarse hair and hair loss Fluid retention (oedema, pleural effusions, ascites) Heavy or irregular periods Constipation
What is primary hypothyroidism
Caused by thyroid gland insufficiency.
Thyroid hormones (i.e. free T3 and T4) will be low. TSH will be high because there is no negative feedback to the brain, so the pituitary produces lots of TSH to try and get the thyroid working.
TSH and T3/T4 in secondary hypothyroidism
Both are low
Management of hypothyroidism
Replacement of thyroid hormone with oral levothyroxine is the treatment of hypothyroidism
What is levothyroxine
Synthetic T4 which metabolises to T3 in the body
Most common type of thyroid tumour
Papillary tumour(often young females)
Features of papillary carcinoma
Mixture of papillary and colloidal filled follicles
Histologically tumour has papillary projections and pale empty nuclei
Seldom encapsulated
Lymph node metastasis predominate
Haematogenous metastasis rare
Features of follicular adenoma
Usually present as a solitary thyroid nodule
Malignancy can only be excluded on formal histological assessment
Features of follicular carcinoma
May appear macroscopically encapsulated, microscopically capsular invasion is seen. Without this finding the lesion is a follicular adenoma.
Vascular invasion predominates
Multifocal disease rare
Features of medullary carcinoma
C cells derived from neural crest and not thyroid tissue
Familial genetic disease accounts for up to 20% cases
Both lymphatic and haematogenous metastasis are recognised, nodal disease is associated with a very poor prognosis.
Which blood parameter is often raised in medullary carcinoma
Serum calcitonin
Features of anaplastic carcinoma
Most common in elderly females
Local invasion is a common feature
Can cause pressure symptoms
Management of anaplastic carcinoma
Treatment is by resection where possible, palliation may be achieved through isthmusectomy and radiotherapy.
Chemotherapy is ineffective.
What are thyroid lymphomas associated with
Hashimoto’s thyroiditis
Management of papillary and follicular cancer
Total thyroidectomy
followed by radioiodine (I-131) to kill residual cells
yearly thyroglobulin levels to detect early recurrent disease
Which syndrome are medullary thyroid tumours part of
MEN-2
Which antibodies are usually present in grave’s disease and Hashimoto’s thyroiditis
Antithyroid peroxidase(anti-TPO) antibodies which are antibodies against the thyroid gland itself
Antithyroglobulin antibodies
In which conditions are antithyroglobulin antibodies present
Grave’s disease
Hashimoto’s thyroiditis
Thyroid cancer
Limitation of measuring antithyroglobulin antibodies
Antithyroglobulin Antibodies are antibodies against thyroglobulin, a protein produced and extensively present in the thyroid gland.
Measuring them is of limited use as they can be present in normal individuals.
Purpose of ultrasound in thyroid dysfunction
Useful in diagnosing thyroid nodules and distinguishing between cystic (fluid filled) and solid nodules. Ultrasound can also be used to guide biopsy of a thyroid lesion.
When are radioisotope thyroid scans used
Hyperthyroidism and thyroid cancers
What does diffuse high uptake of radioactive iodine indicate
Grave’s disease
What does focal high uptake of radioactive iodine indicate
Toxic multi nodular goitre
Adenomas
What do cold areas in radioisotope thyroid scans indicate
“Cold” areas (i.e. abnormally low uptake) can indicate thyroid cancer
Notable adverse effect of carbimazole
Agranulocytosis
What is subclinical hypothyroidism
TSH raised but T3, T4 normal
no obvious symptoms
Significance of subclinical hypothyroidism
risk of progressing to overt hypothyroidism
risk increased by the presence of thyroid autoantibodies
When should treatment be started for subclinical hypothyroidism
start treatment (even if asymptomatic) with levothyroxine if <= 70 years
‘in older people (especially those aged over 80 years) follow a ‘watch and wait’ strategy, generally avoiding hormonal treatment’
What is thyroid acropachy
Specific graves’ triad of:
digital clubbing
soft tissue swelling of the hands and feet
periosteal new bone formation
Contraindications for radio iodine treatment
Contraindications include pregnancy (should be avoided for 4-6 months following treatment) and age < 16 years.
Thyroid eye disease is a relative contraindication, as it may worsen the condition
What is a branchial cyst
Developmental defect of the branchial arches.
The cyst is filled with acellular fluid with cholesterol crystals and encapsulated by stratified squamous epithelium
What is myxoedema coma
defined as severe hypothyroidism leading to decreased mental status, hypothermia, and other symptoms related to slowing of function in multiple organs
Mx of myxoedema coma
IV thyroid replacement IV fluid IV corticosteroids (until the possibility of coexisting adrenal insufficiency has been excluded) electrolyte imbalance correction sometimes rewarming
