Prolonged coma resulting from massive levothyroxine overdose and the utility of N-terminal prohormone brain natriuretic peptide (NT-proBNP)

Abstract

Introduction: Levothyroxine overdose rarely results in systemic toxicity. We report a case of intentional levothyroxine overdose with a delayed onset coma and delirium lasting two weeks.

Case Summary: A 72-year-old female ingested 12 mg levothyroxine. Initially, she was drowsy but quickly recovered and was well for the following two days. On day-3 post-overdose her mental state gradually deteriorated. She presented to the hospital with agitation, confusion and dyspnoea. Initial vital signs: P128 bpm, BP132/67 mmHg, temperature 38 °C and SpO2 97%RA. Features suggesting thyroid storm were present: fever >38 °C, tachycardia and persistent coma. Serum T4 and T3 were >150 pmol/L (normal: 8–16) and >30.8 pmol/L (normal: 3.2–6.1), respectively. These remained elevated for 11 days. She was treated with propranolol, propylthiouracil and cholestyramine. She remained intubated for two weeks without sedation. Her conscious state improved on day-13, coinciding with normalisation of serum T4. Normal cognition was regained four days later. N-terminal pro-brain natriuretic peptide (NT ProBNP) concentration was increased during coma and peaked 2 days prior to Glasgow Coma Score improving.

Discussion: Our case demonstrates features of thyrotoxicosis and thyroid storm with coma after massive levothyroxine overdose. Coma was associated with an increase in NT-proBNP concentration. This may be a potential marker for brain injury and recovery.

Keywords:

• Thyroxine
• overdose
• coma
• thyroid storm
• encephalopathy

Disclosure statement

The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.

Acknowledgements

We thank Dr Kay Weng Choy for assistance with pathology testing.