Thyroid Peer Support 2014

What hormones are secreted by the thyroid gland? T4 (thyroxine) T3 (tri-iodothyronine) These are referred to as the thyroid hormones and are derivatives of tyrosine Calcitonin (don’t worry about this for now, it will reappear in Block 4!)

What are the 6 steps of thyroid hormone synthesis? Thyroglobulin synthesis Uptake and concentration of iodide (I-) Oxidation of iodide (I-) to iodine (Io) Iodination of thyroglobulin Coupling of 2 iodinated tyrosine molecules to form T4 or T3 Secretion

Hypothalamus TRH Anterior pituitary TSH Thyroid T3 T4

Transport of thyroid hormones Are lipophilic so hard to dissolve in blood and so are transported bound to proteins 70% by TBG (thyroxine binding globulin) 30% by albumin Transported as T4 Converted by deiodinases to T3 to effect on the cells.

Hyperthyroidism Caused by thyrotoxicosis (high T3T4) Signs and symptoms link to HIGH metabolic rate Weight and muscle loss Increased appetite Heat intolerance and sweating Anxiety/irritability

Grave’s Disease Autoimmune disease Body’s immune system produces Thyroid Stimulating Antibodies that act on the thyroid to increase T3/T4. Exopthalmos

TSH T3 T4 TRH Hypothalamus High T3T4 levels result in inhibition of TSH and TRH TRH Anterior pituitary TSH Thyroid T3 T4

Hypothyroidism Low T3/T4 Signs and symptoms relate to a lowered metabolic rate Weight gain Lethargy Alopecia Sensitive to cold Slow movements

Causes of hypothyroidism Autoimmune disease: Hashimoto’s Disease Iodine deficiency Previous surgery/treatment that have damaged the thyroid Radioactive iodine therapy Thyroidectomy

Goitre Enlarged thyroid gland Causes: Tumour Graves disease Hashimoto’s disease Iodine deficiency Will result in hypothyroidism

Thyroid function quiz Peer support

Question 1 A woman, 43, presents with: weight loss of a stone over the last few weeks associated with an increase in appetite sweating, exophthalmus and goitre What type of thyroid disease might you be expecting (hyper or hypo)? Hyperthyroidism

Question 1b What would you want to measure to diagnose the hyperthyroidism? TSH, T3 and T4 levels in the circulating blood (called a Thyroid Function Test (TFT)).

TSH T3 T4 TRH This patient has: Hypothalamus Low TSH, high T3 and T4 A history of autoimmune diseases What is your primary differential? Hypothalamus TRH Anterior pituitary TSH Grave’s – autoimmune hyperthroidism Thyroid T3 T4

TSH Antibodies T3 T4 TRH Hypothalamus High T3T4 levels result in inhibition of TSH and TRH TRH Anterior pituitary TSH Antibodies Grave’s where Thyroid stimulating immunoglobulin (TSI) stimulates the thyroid to produce T4 and 3 – these feedback to the hypothalamus and pituitary to suppress TSH Thyroid T3 T4

TSH T3 T4 TRH TUMOUR If instead the TFTs showed: Hypothalamus high T4 and T3 elevated TSH where might the issue in the hormone axis be? Hypothalamus TRH Anterior pituitary TUMOUR TSH Hypothalamus or pituitary Thyroid T3 T4

Question 2 A 37 year old man presents with: Weight gain (with poor appetite) Slow and lethargic Feeling cold What type of thyroid disease would you expect from these symptoms? Hypothyroidism

TSH T3 T4 TRH Hypothalamus You find: The patient had throat cancer 1yr ago that was successfully treated with external beam radiation High TSH, low T3 and T4 What has caused the hypothyroidism? TRH Anterior pituitary TSH Thyroid Damage from radiation to the thyroid gland T3 T4

Any questions? D.white.1@warwick.ac.uk