Gravesí thyrotoxicosis and pregnancy: a case of resistant thyrotoxicosis with Propylthiouracil treatment

M Reddy, R Ratnasabapathy, D Papadopoulou, E Hatfield

Charing Cross Hospital, Imperial College.

A 34 year old woman was referred to the endocrinology clinic in September 2013 with symptoms suggestive of thyrotoxicosis. The initial thyroid function tests showed a TSH of <0.05mU/L and a T4 of 33.9pmol/L. She was commenced Carbimazole 30mg. The TSH receptor antibodies were positive confirming a diagnosis of Gravesí Disease. In January 2014 she was euthyroid on 10mg of Carbimazole and decided she wanted to try for a 3rd pregnancy. She had two young children (aged 3 years and 21 months) at home and therefore radioiodine was not an option. As per guidelines she was switched to Propylthiouracil (PTU) 50mg and started on Folic Acid 5mg.† In July 2014 her TSH became suppressed and her PTU dose was increased to 50mg tds and she was advised to use contraception until normal thyroid function achieved. Between July 2014 and April 2015 the TSH remained suppressed on the PTU and she was therefore switched back to Carbimazole (20mg od). In mid-September 2015 she was seen in clinic at which point she was 5-6 weeks pregnant with TFT as follows: TSH 0.01mU/L, T3 9.3pmol/L and T4 21.7pmol/L. We increased the Carbimazole to 25mg od but this was then decreased to 15mg daily in view of blood tests performed in clinic on 9th November 2015 (TSH 0.06, T4 9.1, T3 4.4). She has been referred to the joint antenatal clinic for ongoing care during pregnancy.

Points for discussion:

  1. What is a safe dose of Carbimazole in early pregnancy?
  2. When planning pregnancy in Gravesí Disease should Carbimazole always be switched to PTU if they are well-controlled on Carbimazole?
  3. Is compliance an issue?