The incidence of febrile convulsions (FCs) among 63 children with congenital hypothyroidism (CH) was compared to that of control children and patient’s siblings in a study at Niigata University, Japan. Patients had been treated with L-thyroxine from 1 month of age. FCs had occurred in only one child with CH (1.6%) compared to 8.2% of control children, 9.5% of the patient’s siblings, and 6.4% of the patient’s parents. 
COMMENT. Children with congenital hypothyroidism who have been treated regularly with thyroid hormone are less prone to have febrile convulsions. A review of systemic electrolyte and neuroendocrine mechanisms of epilepsy  found that Timiras PS and Woodbury DM conducted much of the early experimental work on thyroid imbalance and seizures. Timiras showed that thyroxine increased brain excitability in rats, and Woodbury found that an increased seizure threshold in thyroidectomized rats was lowered by giving thyroid hormone. These alterations in brain excitability were correlated with changes in brain electrolytes. Clinical studies have demonstrated that seizures that accompany myxoema coma respond to thyroid treatment. Further studies of the influence of thyroid function on childhood seizures are needed.