Methylene blue toxicity following infusion to localize parathyroid adenoma.
The parathyroid glands are small, inconspicuous, and variable in number, colour and position. Their identification is vital for excision of hyper-functioning glands and for preservation of normally functioning ones in patients undergoing thyroidectomy. Intravenous infusion of methylene blue at a dose of 7.5 mg/kg is commonly used to aid visualization of the parathyroid glands intra-operatively. Methylene blue is generally considered benign, and there are only two cases published in the literature reporting toxicity following intravenous infusion--such toxicity is a diagnosis of exclusion. We report a case of methylene blue toxicity resulting in expressive aphasia, confusion and disinhibition following infusion for parathyroid adenoma localization. The patient made a complete recovery over 48 hours. Methaemoglobinaemia was excluded as a cause. We suggest that the mechanism of toxicity was a direct effect of methylene blue, although an adverse interaction with serotonin re-uptake inhibitors could not be excluded. In keeping with the UK National Poisons Information Service recommendations, we have altered our practice and now use methylene blue at a dose not exceeding 4 mg/kg. This has not affected our success rate for identification of parathyroid glands. We report this case to highlight the rare occurrence of methylene blue toxicity when used at a dose of 7.5 mg/kg.
Majithia
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Department of Otolaryngology, Royal Free Hospital, London, UK. anoojmajithia@hotmail.com
Stearns
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MP
D000236:Adenoma / Q000175:diagnosis / Q000601:surgery*; D004396:Coloring Agents / Q000008:administration & dosage / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008751:Methylene Blue / Q000008:administration & dosage / Q000009:adverse effects*; D008875:Middle Aged; D010282:Parathyroid Neoplasms / Q000175:diagnosis / Q000601:surgery*; D011183:Postoperative Complications / Q000139:chemically induced*; D012075:Remission, Spontaneous
D004396:Coloring Agents; D008751:Methylene Blue