Endocrine Abstracts

Background: There is controversy about the ideal outcome for radio-active iodine (RAI) treatment in thyrotoxicosis and the optimal dose to be given. Various centres use various doses ranging from 185 mBq to 550 mBq.

Aim: Our aim was to determine the thyroid status post RAI treatment for thyrotoxicosis and in those who became hypothyroid, to assess the time of onset of hypothyroidism from the date of RAI treatment administration.

Methods and results: We audited 32 patients who had RAI treatment between 2003 and 2005 in Glan Clwyd Hospital who were followed up for at least 1 year post RAI treatment. The policy of the hospital is to give 550 MBq to all patients.

The results showed the following:

The mean duration to onset of hypothyroidism was 4 months where 60% were hypothyroid. After 4 months the number of those becoming hypothyroid plateaus reaching 70% at 9 months.

Discussion and conclusion: We compared our results to those in other studies using 550 MBq as well as other doses. We concluded that our data is compatible with other audits done in different parts of the UK. Fixed doses of 550 MBq resulted in low failure rates and obviates the need for long term follow up in secondary care but with a high rate of hypothyroidism. We also found out in our audit that most patients become hypothyroid within the first 4 months following RAI treatment. In a recent study by Franklyn et al. in Birmingham, patients treated with RAI were found to have increased mortality and this was attributed to ischaemic heart disease as a result of subclinical hypothyroidism. This supports treating hyperthyroidism with doses of radioiodine sufficient to induce overt hypothyroidism.