Seizure in a child after an acute ingestion of levothyroxine

Abstract

Background: Unintentional ingestion of thyroid hormone preparations is a common occurrence reported to poison control centers. These incidents rarely result in serious outcomes. We report a case of a tonic-clonic seizure occurring in a child after ingestion of a maximum of 3.6 mg of levothyroxine.

Case report: A 3.5-year-old boy ingested up to 41 tablets of 88 microg levothyroxine, which was not discovered until the following day. On the third day after the ingestion, he had a single 5- to 10-minute tonic-clonic seizure. Laboratory results were total thyroxine greater than 24.0 microg/dL; free thyroxine, 5.5 ng/dL; and thyroid-stimulating hormone, 0.03 mU/L. On the following day, the patient had diarrhea and was hyperactive; heart rate was 144 beats per minute, and mild hyperreflexia was noted on neurological examination. Symptoms were resolved 3 days later.

Conclusion: This is the second case report of a seizure occurring in a child after an unintentional ingestion of levothyroxine. The maximum amount possibly ingested is much lower than that previously reported. Pediatric ingestion of less than 5 mg of levothyroxine may result in serious outcomes.