Novel Cause of ‘Black Thyroid’: Intraoperative Use of Indocyanine Green

The antibiotic minocycline is virtually pathognomonic for brown-black discoloration of the thyroid gland referred to as ‘black thyroid’. Black thyroid’ is an incidental finding in patients taking the drug who undergo thyroid surgery for another indication and is not of known clinical significance. However, its recognition is important so as not to raise concern for a disease process. Here, we present the first case of ‘black thyroid’ attributable to the iodine-containing compound indocyanine green. Intraoperative indocyanine green was administered as part of a research protocol transoral robotic-assisted surgery for a base of tongue cancer in a 44-year-old man. Hemithyroidectomy was subsequently performed during the same operation for further evaluation of an indeterminate thyroid nodule. The resected thyroid lobe was dark, nearly black in color, and histologically showed extensive brown pigment deposition in the follicular epithelial cells and colloid, mimicking minocycline-induced ‘black thyroid’. In this case, however, the patient was not taking minocycline; instead the ‘black thyroid’ was attributed to the iodine-containing compound indocyanine green. Indocyanine green is a hereto unreported cause of ‘black thyroid’ with histopathologic features that are remarkably similar to that induced by minocycline. Indocyanine green should be included the differential diagnosis of ‘black thyroid’. Clinical history is important so as not to raise concern for a disease process.