Reliable identification of parathyroid glands is critical to the success of thyroid and parathyroid surgery. In thyroid surgery, inadvertent injury to parathyroid glands may cause temporary or permanent hypoparathyroidism (low calcium levels needing long term treatment). In parathyroid surgery, early identification of normal and/or enlarged parathyroid glands helps in deciding on the extent of surgery and increases the chances of postoperative normal calcium levels.

Methylene Blue (Methylthioninium chloride, MB) is a dye that when given intravenously in high doses, is taken up differently by thyroid and parathyroid tissue. It is currently used during parathyroid surgery by some surgeons to help identify enlarged parathyroid glands by visual examination alone. Such visual examination is unhelpful in the identification of 'normal' parathyroid tissue. MB exhibits fluorescent properties in the near-infrared range (light just beyond the visible spectrum). This can be picked up by an appropriate imaging system. This has potential to identify and differentiate between 'normal' parathyroid, 'abnormal' parathyroid and thyroid tissue during surgery.

The investigators have established the feasibility of the intra-operative use of a near infra-red fluorescent imaging device called Fluobeam® and demonstrated the ability of this device to pick up near infra-red fluorescence from human tissue after administration of intravenous MB. Animal experiments have shown that doses as low as 0.1mg/kg of MB given intravenously enable fluorescent visualisation of thyroid and parathyroid glands.

This study will aim to optimise the dose and timing of administration of MB in human thyroid and parathyroid surgery and to develop a protocol which would then subsequently be assessed for effectiveness in a multi-centred randomized controlled setting.

Around 13,000 thyroid and parathyroid operations are performed per year in England for both benign and malignant disease. Reliable identification of parathyroid glands is critical to the success of thyroid and parathyroid surgery. In thyroid surgery, inadvertent injury to parathyroid glands may cause temporary or permanent hypoparathyroidism (low calcium levels needing long term treatment); the latter is associated with significant long term problems. In parathyroid surgery, early identification of normal and/or enlarged parathyroid glands helps in deciding on the extent of surgery and increases the chances of postoperative normal calcium levels.

Methylene Blue (Methylthioninium chloride, MB) is a dye that when given intravenously in high doses, is taken up differently by thyroid and parathyroid tissue. It is currently used during parathyroid surgery by some surgeons to help identify enlarged parathyroid glands by visual examination alone. At these doses, there is a risk of adverse effects from administration of MB. Such visual examination is unhelpful in the identification of 'normal' parathyroid tissue. MB is not currently used in surgery for thyroid pathologies. MB exhibits fluorescent properties in the near-infrared range (light just beyond the visible spectrum). This can be picked up by an appropriate imaging system. This has potential to identify and differentiate between 'normal' parathyroid, 'abnormal' parathyroid and thyroid tissue during surgery.

The investigators have established the feasibility of the intra-operative use of a near infra-red fluorescent imaging device called Fluobeam® and demonstrated the ability of this device to pick up near infra-red fluorescence from human tissue after administration of intravenous MB. Animal experiments have shown that doses as low as 0.1mg/kg of MB given intravenously enable fluorescent visualisation of thyroid and parathyroid glands.

This study will aim to optimise the dose and timing of administration of MB in human thyroid and parathyroid surgery and to develop a protocol which would then subsequently be assessed for effectiveness in a multi-centred randomized controlled setting.

Inclusion Criteria:

-All patients undergoing either a total thyroidectomy or bilateral neck exploration for PHPT in Sheffield Teaching Hospitals NHS Foundation Trust

Exclusion Criteria:

• Patients undergoing re-do procedures
• Patients unable to understand spoken and written English
• Patients unable to give adequate informed consent
• Patients with a history of intolerance or sensitivity to MB
• Patients with known G6PD deficiency
• Patients on serotonin reuptake inhibitors
• Patients undergoing surgery for thyroglossal cyst and
• Patients undergoing thoracic exploration; either alone or in combination with a neck exploration