Thyroid Flashcards
Around ?% of the UK population has hypothyroidism (an under active thyroid gland) whilst around ?% have thyrotoxicosis (an over active gland).
Around 2% of the UK population has hypothyroidism (an under active thyroid gland) whilst around 1% have thyrotoxicosis (an over active gland).
Both hypothyroidism and hyperthyrodism (also known as thyrotoxicosis) are around 10 times more common in women than men.
true
The thyroid gland is one of the largest endocrine organs in the body.
true
Describe the hypothalamus-pituitary-end organ system in thyroid
hypothalamus secretes thyrotropin-releasing hormone (TRH) which stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH). This then acts on the thyroid gland increasing the production of thyroxine (T4) and triiodothyronine (T3), the two main thyroid hormones. These then act on a wide variety of tissues, helping to regulate the use of energy sources, protein synthesis, and controls the body’s sensitivity to other hormones.
How are hypothyroid problems classified?
primary hypothyroidism: there is a problem with the thyroid gland itself, for example an autoimmune disorder affecting thyroid tissue (see below)
secondary hypothyroidism: usually due to a disorder with the pituitary gland (e.g.pituitary apoplexy) or a lesion compressing the pituitary gland
congenital hypothyroidism: due to a problem with thyroid dysgenesis or thyroid dyshormonogenesis
there are a number of causes thyrotoxicosis the vast majority are primary in nature
true
secondary hyperthyroidism is rare
true
1% of cases
Congenital thyrotoxicosis is common
false
Congenital thyrotoxicosis is not seen
The majority of thyroid problems seen in the developed world are a consequence of
autoimmunity.
Most common cause thyrotoxicosis
Graves’ disease
Most common cause of hypothyroidism?
Hashimoto’s thyroiditis
most common cause in the developed world
What is hashimotos associated with?
autoimmune disease, associated with type 1 diabetes mellitus, Addison’s or pernicious anaemia
What does hashimotos cause in the acute phase?
transient thyrotoxicosis
List causes of hypothyroid
Hashimotos Subacute thyroiditis (de Quervain's) Riedel Thyroiditis Postpartum thyroiditis Drugs Iodine deficiency
Which drugs cause hypothyroid
lithium
amiodarone
the most common cause of hypothyroidism in the developing world
Iodine deficiency
Which drugs cause thyrotoxicosis
amiodarone
Can also cause hypothyroidism?
Toxic multinodular goitre causes which thyroid picture? What causes it
Thyrotoxicosis
autonomously functioning thyroid nodules that secrete excess thyroid hormones
How does Subacute thyroiditis (de Quervain’s) present
associated with a painful goitre and raised ESR
How does Riedel’s thyroiditis present
fibrous tissue replacing the normal thyroid parenchyma
causes a painless goitre
Symptoms of hypothyroidism?
Weight gain, Lethargy, Cold intolerance, Constipation
Menorrhagia
Decreased deep tendon reflexes
Carpal tunnel syndrome
Dry (anhydrosis), cold, yellowish skin
Non-pitting oedema (e.g. hands, face)
Dry, coarse scalp hair, loss of lateral aspect of eyebrows
Symptoms of thyrotoxicosis
Weight loss
‘Manic’, restlessness
Heat intolerance
Palpitations, may even provoke arrhythmias e.g. atrial fibrillation
Increased sweating
Pretibial myxoedema: erythematous, oedematous lesions above the lateral malleoli
Thyroid acropachy: clubbing
Diarrhoea
Oligomenorrhea
Anxiety, Tremor
TFTs - what does this look at ? How useful is this
these primarily look at serum TSH and T4 levels
T3 can be measured but is only useful clinically in a small number of cases
remember that TSH and T4 levels will often be ‘opposite’ in cases of primary hypo- or hyperthyroidism. For example in hypothyroidism the T4 level is low (i.e. not enough thyroxine) but the TSH level is high, because the hypothalamus/pituitary has detected low levels of T4 and is trying to get the thyroid gland to produce more
TSH levels are more sensitive than T4 levels for monitoring patients with existing thyroid problems and are often used to guide treatment
Describe TFTs in Thyrotoxicosis (e.g. Graves’ disease)
TSH Low
Free T4 High
Describe TFTs in Primary hypothyroidism (e.g. Hashimoto’s thyroiditis)
TSH High
Free T4 Low
Describe TFTs in Secondary hypothyroidism? What is required in addition to main tx
TSH Low
Free T4 Low
Replacement steroid therapy is required prior to thyroxine
Describe TFTs in Sick euthyroid syndrome
TSH Low
Free T4 Low
Common in hospital inpatients. Changes are reversible upon recovery from the systemic illness and no treatment is usually needed
T3 is particularly low in these patients
Describe TFTs in Subclinical hypothyroidism
TSH High
Free T4 Normal
This is a common finding and represents patients who are ‘on the way’ to developing hypothyroidism but still have normal thyroxine levels. Note how the TSH levels, as mentioned above, are a more sensitive and early marker of thyroid problems
Describe TFTs in Poor compliance with thyroxine
TSH High
Free T4 Normal
Patients who are poorly compliant may only take their thyroxine in the days before a routine blood test. The thyroxine levels are hence normal but the TSH ‘lags’ and reflects longer term low thyroxine levels
A number of thyroid autoantibodies can be tested for (remember the majority of thyroid disorders are autoimmune). The 3 main types are:
Anti-thyroid peroxidase (anti-TPO) antibodies
TSH receptor antibodies
Thyroglobulin antibodies
There is significant overlap between the type of antibodies present and particular diseases
true
but generally speaking TSH receptor antibodies are present in around 90-100% of patients with Graves’ disease and anti-TPO antibodies are seen in around 90% of patients with Hashimoto’s thyroiditis.
Other tests (other than TFTs)
nuclear scintigraphy; toxic multinodular goitre reveals patchy uptake
In T3 thyrotoxicosis the free T4 will be
normal
Graves’ disease is the most common cause of thyrotoxicosis. It is typically seen in women aged
30-50 years
Specific signs seen in Grave’s but not in other causes of thyrotoxicosis
eye signs (30% of patients)
pretibial myxoedema
thyroid acropachy, a triad of: digital clubbing, soft tissue swelling of the hands and feet, periosteal new bone formation
Autoantibodies in Grave;s
TSH receptor stimulating antibodies (90%)
anti-thyroid peroxidase antibodies (75%)
Graves’ disease accounts for around 50-60% of cases of thyrotoxicosis. Other
Causes
Graves’ disease
toxic nodular goitre
acute phase of subacute (de Quervain’s) thyroiditis
acute phase of post-partum thyroiditis
acute phase of Hashimoto’s thyroiditis (later results in hypothyroidism)
amiodarone therapy
Thyroid eye disease affects between ?% of patients with Graves’ disease.
25-50%
Pathophysiology of thyroid eye disease
it is thought to be caused by an autoimmune response against an autoantigen, possibly the TSH receptor → retro-orbital inflammation
the inflammation results in glycosaminoglycan and collagen deposition in the muscles
Prevention of thyroid eye disease?
smoking is the most important modifiable risk factor for the development of thyroid eye disease
radioiodine treatment may increase the inflammatory symptoms seen in thyroid eye disease. In a recent study of patients with Graves’ disease around 15% developed, or had worsening of, eye disease.
Prednisolone may help reduce the risk
Features of thyroid eye disease?
the patient may be eu-, hypo- or hyperthyroid at the time of presentation
exophthalmos
conjunctival oedema
optic disc swelling
ophthalmoplegia
inability to close the eyelids may lead to sore, dry eyes. If severe and untreated patients can be at risk of exposure keratopathy
Management thyroid eye disease?
topical lubricants may be needed to help prevent corneal inflammation caused by exposure
steroids
radiotherapy
surgery
Monitoring patients with established thyroid eye disease the following symptoms/signs should indicate the need for urgent review by an ophthalmologist?
unexplained deterioration in vision
awareness of change in intensity or quality of colour vision in one or both eyes
history of eye suddenly ‘popping out’ (globe subluxation)
obvious corneal opacity
cornea still visible when the eyelids are closed
disc swelling
What is thyroid storm?
Thyroid storm is a rare but life-threatening complication of thyrotoxicosis. It is typically seen in patients with established thyrotoxicosis and is rarely seen as the presenting feature. Iatrogenic thyroxine excess does not usually result in thyroid storm.
