Methylene blue has been used to help facilitate parathyroid surgery for over 30 years. Its use has been widely considered both safe and cost effective. Twenty-six cases of a toxic metabolic encephalopathy, however, have been reported with its use. As a result, some surgeons have stopped using this technique altogether. It is now known that methylene blue is a monoamine oxidase inhibitor. When combined with drugs that increase central serotonin neurotransmission, serotonin toxicity results. This is the cause of the encephalopathy described in the literature. A case report, review of the literature, and guidelines as to its proper use are presented so as to allow for safe parathyroid surgery.

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