Thyrotoxicosis Quiz

Well done

Thyroid hormone synthesis is comprised of a number of steps, all of which are TSH dependent

• Iodine taken up by the thyroid
• Iodine is oxidised and organified
• The iodine is then bound to thyroglobulin.

The last 2 steps are controlled by thyroid peroxidase

Next, Thyroid Hormone (TH) is released, and circulating TH is 99% bound to thyroxine binding globulin

There are 2 forms of TH, T3 and T4.  T3 is more potent than T4, and about 10-20% of circulating T3 is released from the thyroid, the rest is converted from T4 by peripheral deiodonases.

Well Done

Anti-TPO antibodies are typical in Hashimoto’s disease but also present in 50-80% of Grave’s patients.  Exopthalmos is diagnostic of Grave’s disease.  TSH levels are typically supressed in Grave’s disease due to negative feedback to the pituitary.  Hashimotos can also cause hyperthyroidism due to transient increase in release of preformed thyroid hormone early in the illness.

Well Done.

PTU is the preferred drug in pregnancy because Carbimazole is teratogenic.  Carbimazole is dosed once a day, whilst PT needs to be dosed three times a day.  While carbimazole is often started in patients with undifferentiated hyperthyroidism, it is of no use in patients whose hyperthyroidism is due to release of preformed thyroid hormone – viral thyroiditis, de Quervain’s, Hashimoto’s.  It is however of great value in patients whose hyperthyroidism is due to oversynthesis of new TH (Grave’s, toxic adenomas, toxic multinodular goitre).  Propanolol is the preferred beta blocker for thyrotoxic patients due to its poor selectivity (β-1 and β-2 activity and ability to cross the blood brain barrier, and so treat the broad range of sympathetic symptoms associated with thyrotoxicosis (anxiety, tremor, tachycardia, hypertension, etc).