Résumé
A 14-year-old girl presented with severe headache and grand mal seizure. A magnetic resonance imaging(MRI) of brain showed a pituitary mass(1.0X1.5X1.3cm) incidentally during seizure evaluation. On physical examination, nodular goiter was detected on her anterior neck. The hormone study showed markdly increased basal thyroid stimulating hormone(TSH) level compared to thyroid hormone level, hyperprolactinemia and decreased basal growth hormone level. TSH and prolactin showed exaggerated response to thyrotropin releasing hormone(TRH) and the growth hormone showed delayed and blunted response to insulin-induced hypoglycemia. With the results of thyroid autoantibody and thyroid scan, the diagnosis of Hashimoto's thyroiditis was possible. Thyroid hormone and anticonvulsant drug were started with close observation of clinical status under the impression of pituitary feedback adenoma caused by hypothyroidism. After 3 months replacement therapy of levothyroxine sodium, she achieved euthyroid state with disappearance of headache and nodular goiter. After continuous replacement therapy for 9 months more, the pituitary mass was successfully regressed on follow up MRI with normalization of basal prolactin level. Grand mal seizure was developed after withholding anticonvulsant drug even though continuous admmistration of thyroid hormone. Because of similarity among pituitary adenoma discovered incidentally, careful hormonal study and high index of suspicion should be maintained to achieve correct diagnosis in order to avoid unnecessary pituitary surgery in these patients.