The study
A study was undertaken to find any association between ‘hypothyroxinaemia’ (low T4 + normal TSH) and ADHD. Thyroxinaemia is a state where pregnant women with generally normal thyroid function have a transient reduction in thyroxine levels with a normal TSH.
This was a population-based cohort study in Holland of 3,873 mother-baby pairs, of which 127 had mothers with hypothyroxinaemia.
Thyroxine (T4) levels were measured at the first antenatal visit (on average at 13.6 weeks). Symptoms of ADHD were assessed in the eight-year-olds using the Conners’ Parent Rating Scale (range = 0-36, where higher scores mean more symptoms). TPO levels were also measured.
The findings
1 Maternal hypothyroxinaemia in early pregnancy was associated with 7% higher ADHD scores in children (at eight years-old).
2 This association persisted even after adjustments were made for potential confounding factors (eg. ethnicity, sex of child, ethnicity, age of mother, co-existing autism and other factors), and after mothers with raised TPO antibody levels were removed from the data analysis.
3 Interestingly, the omission of mothers who took thyroxine medication had a minimal impact on this association.
4 There was no association between maternal subclinical hypothyroidism and ADHD symptoms in the children.
What this means for GPs
GPs should be aware of the association (albeit modest) between hypothyroxinaemia and ADHD.
We should be aware of hypothyroxinaemia as a condition where T4 levels are low, but TSH levels are normal. Hence in patients in the early stages of their pregnancy, with symptoms of or a history of hypothyroidism, it is important to check T4 levels and not rely solely on TSH levels.
Hypothyroxinaemia should be treated promptly and effectively. Considering the finding that there was minimal impact on the association even after mothers who took thyroxine were removed, I would personally strongly consider consulting with an endocrinologist before initiating treatment.
The paper
JAMA (Journal of the American Medical Association), July 2015
Dr Hamed Khan is a GP in the emergency department of St George’s, London, and a clinical lecturer. He tweets as @drhamedkhan
