Black Thyroid, also sometimes called Black Thyroid Syndrome or Black Thyroid Disease is a rare pigmented change of the thyroid gland seen almost exclusively in people taking minocycline, an antibiotic used to treat a number of bacterial infections such as pneumonia, as well as in the treatment of acne and rheumatoid arthritis.
It is recognised that when the antibiotic minocycline reacts with thyroid peroxidase it can form a black pigment to the thyroid gland. People with Black Thyroid Disease often also have hypothyroidism, hyperthyroidism, neck swelling, thyroid cancer, a nodule or no symptoms at all, but it is a very rare condition, with just sixty-one cases reported to date. 
A fine needle biopsy does not seem to be a reliable way to find and diagnose Black Thyroid Disease , but it is often discovered incidentally during surgery on the thyroid gland, surgery to remove the thyroid gland – a thyroidectomy – (often due to thyroid cancer) or during an autopsy. 
Despite several case reports of thyroid cancer occurring alongside Black Thyroid Disease, there are no current recommendations that patients taking the antibiotic minocycline undergo additional screening for thyroid cancer. Further research is needed to establish whether a true link exists between black thyroid disease and thyroid cancer.
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