What is the difference between a primary and secondary thyroid disease?
Primary thyroid disease affects the thyroid gland itself. Can occur with or without goitre, and is most commonly autoimmune in origin
Secondary thyroid disease affects the hypothalamus or the pituitary gland, without thyroid involvement.
Describe the Hypothalamic-Pituitary-Thyroid Axis
Thyrotrophin Releasing Hormone (TRH) is released from the Hypothalamus, and acts on Pituitary gland.
This causes release of Thyroid Stimulating Hormone (TSH), aka Thyrotropin, from the Anterior Pituitary, which acts on the Thyroid gland to release T4 (Thyroxin, 80% of hormone secreted) and T3 (Levothyroxine, remaining 20%)
Only T3 is active, T4 needs to be de-iodinated in the Liver to T3
T4 and T3 then have a negative feedback effect on the Pituitary and the Hypothalamus

How would TSH and T3/T4 levels appear in Primary Hypo/Hyperthyroidism?
Primary Hypothyroidism
Primary Hyperthyroidism
How would TSH and T3/T4 levels appear in Secondary Hypo/Hyperthyroidism?
Secondary Hypothyroidism
Secondary Hyperthyroidism
What is myxoedema?
In what condition is Pretibial myxoedema (rarely) seen?
Myxoedema, or myxoedema coma, is a severe hypothyroidism and is a medical emergency
Pretibial myxoedema is a rare clinical sign of Grave’s Disease (i.e. autoimmune hyperthyroidism)
What are some of the causes of Primary Hypothyroidism? Both goitrous and non-goitrous, be sure to get the most common causes!
Goitrous
Non-goitrous
Self-limiting
Generally, what could cause Secondary Hypothyroidism?
Any disease of the Hypothalamus or Pituitary, of which there are many
What is Hashimoto’s Thyroiditis? What is it characterised by?
Most common cause of hypothyroidism in the Western World
Autoimmune destruction of the thyroid gland and reduced hormone production
Often a family history, women more affected than men
Characterised by:
What are some of the clinical features of Hypothyroidism?
Hair and Skin
Thermogenesis
Fluid retention
Cardiac
Metabolic
GI
Respiratory
Neurological
Gynae/reproductive
What does the thyroid auto-antibody profile look like for…
Grave’s
Autoimmune Hypothyroidism
Hypothyroidism - treatment
Normal metabolic rate should be restored gradually, rapid restoration could lead to cardiac arrythmias
Main treatment is levothyroxine (T4)
When is levothyroxine best taken?
What are the benefits of taking both T4 and T3?
How does the dosing change in pregnancy?
T4 is preferrably taken prior to breakfast.
No benefit seen in combining treatments of T4 and T3
Dose requirements may increase by 25-50% during pregnancy
(Calcium supplements and PPIs should also be avoided as these can interfere with the action of levothyroxine)
Myxoedema coma - findings and treatment
Findings
Treatment
What is the difference between Thyrotoxicosis and Hyperthyroidism?
Thyrotoxicosis - the clinical state of the body’s tissues being exposed to excessive amounts of thyroxin
Hyperthyroidism - refers specifically to conditions of overactivity in the thyroid, resulting in thyrotoxicosis
Thyrotoxicosis (hyperthyroidism) - signs and symptoms
Cardiac
Sympathetic
CNS
GI
Vision
Hair and Skin
Reproductive
Muscles
Metabolism
Thermogenesis
What are some of the causes of Thyrotoxicosis associated with Hyperthyroidism?
Excessive thyroid stimulation
Thyroid nodules with autonomous function
What are some of the causes of Thyrotoxicosis not associated with Hyperthyroidism?
Thyroid inflammation
Exogenous thyroid hormones
Ectopic thyroid tissue
Who gets Graves’ disease? What are the TSH and free T3/T4 profiles like?
Women more commonly than men (2:1)
Younger people (age 20-50)
Genetic susceptibility. Sisters and children of women with Graves’ have a 5-8% risk of developing an autoimmune thyroid disease
Smokers - makes Graves’ harder to treat and the disease is a worse form
TSH is low, free T3/T4 is high
What antibody test can be done if Graves’ is suspected?
TSH Receptor Antibody (TRAb) - 70-100% are positive
No need to image thyroid if TRAb is positive
What obvious clinical signs may be seen on inspection in patients with Graves’?
And on auscultation?
What other condition is very noticeable on inspection and could feature in Graves’?
Pretibial myxoedema
Finger clubbing
Thyroid bruits (very rare), only heard in very large goitres
Graves’ Eye Disease (aka thyroid eye disease) - seen in 20% of Graves’ patients
How is Thyroid Eye Disease graded and treated?
Graded with a clinical activity score (CAS, Mourits)
Mild disease is treated with topical lubricants
More severe disease is treated with steroids or radiotherapy. Surgery to decompress can also be used
In which group does nodular thyroid disease more commonly occur? How does it present?
What tests are done to confirm the diagnosis?
Typically presents in older patients
Thyroid may feel nodular, and an asymmetric goitre may be apparent
Tests
Thyroid storm is a medical emergency! What might you see?
How do you treat it?
Severe hyperthyroidism
Respiratory and cardiac collapse - may require mechanical ventilation
Hyperthermia
Exaggerated reflexes
Typically seen in hyperthyroid patients with an acute infection/illness, or recent thyroid surgery
Treatment
Name some anti-thyroid drugs (ATDs).
What is their mechanism of action?
Carbimazole
Propylthiouracil (PTU)