Focus on Hyperthyroidism.
Introduction
The recent meeting of the Society at the Royal College of Paediatrics
and Child Health Annual Meeting in York featured a Clinical Practice session
on thyroid disease. Several issues were raised with respect to the use
of radioactive iodine in the treatment of hyperthyroidism.
How safe is radioactive iodine therapy for the treatment of hyperthyroidism?
There are only a few population studies of the long-term effects of
radioactive iodine therapy and these are effectively confined to adults.
As such the role that this modality should play in the management of hyperthyroidism
in children is unclear. A recent publication sheds some light on mortality
in patients with this condition under the age of 50 years (1). This large
cohort study of 7209 subjects treated with 105,028 person-years follow-up
revealed a slight excess of deaths from all causes with a standardised
mortality ratio (SMR) of 1.1. This compares with similar values from USA
(SMR 1.3) (2) and Sweden (SMR women 1.5; men 1.3) (3).
In the under 50 age group deaths were increased in the first year of
therapy from endocrine (effectively thyroid) (SMR 2.5 95%CI 1.4 - 4.1)
disease. Cardiovascular disease mortality was not increased (SMR 1.2 95%CI
0.9 - 1.4).
Treating hyperthyroidism in the presence of eye disease
Eye disease precedes hyperthyroidism in 20%, appears at the same time
in 40% and after diagnosis in the rest. Smoking worsens the risk of eye
problems (Odds Ratio 7.7). An RCT of methimazole versus radioactive iodine
demonstrated increase in problems after radioactive iodine (4). Odds Ratio
for worsening opthalmopathy - Methimazole (n = 148) 1.0 ; Radioactive iodine
(n = 150) 4.3
Absolute risk increase 0.1. Number needed to treat = 10. Can treat 10
individuals with radioactive iodine and expect only one to have worsening
of signs.
Comment
In the under 50 years of age individual radioactive iodine would appear
to be effective and safe. Slight worsening of eye signs can be expected
but these are mild. Prednisolone cover is only necessary in smokers and
those with elevated serum T3 levels (5). Cancer risk is unclear; unchanged
in the Birmingham study) and slightly elevated for respiratory and gastric
lesions in Sweden (6).
The recent Royal College of Physicians Guidelines on the use of radioactive
iodine specifically recommends that children and pregnant women do not
receive treatment. Therapy in paediatric and adolescent practice should
only be conducted within the framework of an ongoing National Audit reporting
system with central tagging within the Cancer and National Deaths Registers.
References
1 Franklyn JA, Maisonneuve R Sheppard MC, Betteridge J Boyle R Mortality
after the treatment of hyperthyroidism with radioactive iodine. New EngI
J Med 1998; 338: 712-8.
2. Goldman MB, Maloof F Monson RR, Aschengrau A, Cooper DS, Ridgeway
EC. Radioactive iodine therapy and breast cancer a follow-up study of hyperthyroid
women. Am J Epidemiol 1988127: 969-80.
3. Hall P, Lundell S, HoIm LE. Mortality in patients treated for hyperthyroidism
with iodine-131. Acta Endocrinol 1993128: 230-4.
4. Bartalena L, Marcocci C, Bogazzi F, et al. Relation between therapy
for hyperthyroidism and the course of Graves' ophthalmopathy. New EngI
J Med 1998; 338: 73-8.
5. Tallstedt L, Lundell G, Torring 0, et al. Occurrence of ophthalmopathy
after treatment for Graves' hyperthyroidism.. New Engl J Med 1992; 326:1733-8.
6. Hall P, Berg G, Bjelkengen et al. Cancer mortality after iodine-137
therapy for hyperthyroidism. Int J Cancer 1992; 50: 886-90.
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