Therapeutic Plasma Exchange for Severe Exogenous Thyrotoxicosis Following Massive Levothyroxine Ingestion: A Case Report

Levothyroxine is among the most commonly prescribed medications worldwide and is generally safe at therapeutic doses; however, massive ingestion can result in severe exogenous thyrotoxicosis and delayed progression to thyroid storm. Management is challenging because clinical deterioration may occur days after ingestion due to the peripheral conversion of thyroxine (T4) to triiodothyronine (T3) and standard medical therapies do not directly remove circulating hormone. We report the case of a 70-year-old male patient with a massive levothyroxine overdose involving the ingestion of approximately 8,000 mcg, leading to worsening thyrotoxicosis with features concerning impending thyroid storm treated with beta-blockade, corticosteroids, and cholestyramine. Given the large intravascular burden of protein-bound T4 and clinical deterioration, therapeutic plasma exchange (TPE) was initiated. Serial TPE resulted in rapid biochemical improvement with marked reductions in free T4 levels and corresponding clinical stabilization. This case highlights the delayed and potentially misleading presentation of massive levothyroxine ingestion and demonstrates the effectiveness of TPE as a rescue therapy in severe exogenous thyrotoxicosis. Early recognition, prolonged monitoring, and consideration of TPE are essential when life-threatening symptoms emerge following massive levothyroxine overdose.