Thyroid disease basics Flashcards
What is meant by thyroid disease?
Thyroid diseases are conditions characterised by a change in thyroid hormone function
What are the two categories of thyroid disease?
Primary
Secondary
What is meant by primary thyroid disease?
Disease affecting the thyroid gland itself
What is meant by secondary thyroid disease?
Disease affecting the hypothalamus or pituitary gland, which causes a resulting change in thyroid function
What are some hormones that can be measured in thyroid disease?
Thyroid Stimulating Hormone (TSH)
Free T4
Free T3
Binding proteins
Where is TSH released from?
Thyrotroph cells in the anterior pituitary gland
What is hypothyroidism?
Insufficient secretion of thyroid hormones from the thyroid gland (Underactive thyroid)
What is myxoedema?
Severe hypothyroidism
What is pre-tibial myxoedema?
A rare clinical sign of Grave’s disease, an autoimmune thyroid disease which results in hyperthyroidism, causing erythematous plaque formation on the legs
What is sub-clinical hypothyroidism?
A condition in which there is high TSH levels, with no clinical symptoms and T3/T4 at normal range
What is thyrotoxicosis?
The clincial, physiological and biochemical state arising when tissues are exposed to excess thyroid hormone
What is hyperthyroidism?
Refers specifically to conditions in which overactivity of the thyroid gland leads to thyrotoxicosis (Overactive thyroid)
What is a goitre?
A goitre is any enlargement of the thyroid gland, caused by impaired synthesis of thyroid hormone
What is the most common cause of goitre formation?
This is most commonly due to lack of dietary iodine or lack of bio-availability of iodine
How does iodine deficiency lead to goitre formation?
Reduced iodine levels mean there is less iodide present to synthesise T3 and T4
Reduced T3/4 production causes rise in TSH, stimulating gland enlargement, in order to maintain a euthyroid state
What are the 2 types of goitre?
- Diffuse (Non-toxic)
- Multi-nodular (Toxic)
What are diffuse goitres?
Diffuse goitres are an enlargement of entire thyroid gland, without formation of nodules
What are the 2 types of cause of diffuse goitres?
They can be endemic, meaning they occur in >10% of a population, or they can be sporadic
What causes endemic diffuse goitre formation?
Endemic diffuse goitres are usually caused by iodine deficiency or goitrogenic substances
What are goitrogenic substances?
Goitrogenic substances are those with a very high iodine content such as smoking, disulphides and lithium
Where are endemic diffuse goitres most commonly found?
In mountainous regions
What are some causes or risk factors of sporadic diffuse goitre formation?
Sporadic diffuse goitres most commonly occur in females and are thought to be associated with puberty
They may also be caused by ingestion of substances limiting T3/4 production or inborn errors of metabolism (Dyshormonogenesis)
What is a possible complication of dyshormonogenesis in children?
Cretinism
How do diffuse goitres usually present?
Diffuse goitres usually don’t cause changes in thyroid hormone levels, but instead present with mass effects
What is the main cause of multi-nodular goitre formation?
Multi-nodular goitres usually evolve from longstanding, simple goitres via recurrent hyperplasia and involution
Describe the pathology of multi-nodular goitre formation
Mutations of TSH signalling pathways in the thyroid lead to variation of response of follicular cells to external stimuli, as well as formation of fibrous bands, causing nodule formation
What are some possible complications of multi-nodular goitre?
This can lead to follicular rupture, haemorrhage, scarring and calcification, as well as mass effects
They may also develop into an autonomous nodule, leading to hyperthyroidism
What are some examples of mass effects caused by goitre formation?
- Cosmetic changes
- Airway obstruction
- Vessel compression
How can thyroid disease affect conception?
Hypothyroidism and hyperthyroidism causes anovulatory cycles which can reduce fertility
Anovulatory cycles are menstrual cycles in which there is no luteal phase or ovulation
Why does pregnancy increase demand on the thyroid?
Maternal thyroxine is important for neonatal development, especially of the CNS
This means that during pregnancy, there is an increased demand on the thyroid during pregnancy
