(0402) Black Thyroid: A Scoping Review

Introduction: The first report of a black thyroid in humans was described in 1976. Since then, many cases of black thyroid discoloration has been associated with tetracycline use presumed due to lipofuscin mixed with drug products in cells. However, our understanding of this discoloration, association with malignancy, and triggering agents remains limited.

Methods: A scoping review was performed utilizing a MEDLINE search, resulting in 73 articles discussing “black thyroid.” A total of 38 case reports, 3 case series, and 2 retrospective institutional reviews were identified. The age, sex, thyroid pathology, and presumed offending agent were recorded in each case. STATA was used for analysis.

Results: A total of 59 cases from single reports and series were compiled. Of them, 64% were female (38 patients), and 36% were male (21 patients). The mean age was 42 (range 18-78). The associated agent for the black thyroid was reported as minocycline alone in 58% of cases (34 patients) and in 29% the trigger was unknown. The remainder included minocycline in addition to doxycycline or tetracycline, tetracycline alone, lithium and tricyclic antidepressants, and intraoperative indocyanine green. Of the black thyroids, 24% were found incidentally on autopsy; 21.7% (13 patients) had black thyroid discovered on surgical removal of papillary thyroid carcinoma (PTC) or of a benign adenoma (11%). Overall a 30% rate of malignancy was reported among surgically removed black thyroids. One institution in the US completed 2 retrospective reviews including one of nearly 1,000 patients, and found statistically significant association of black thyroid with increased risk of malignancy, with 55.4% in black thyroids and 32.8% in non-black thyroids.

Conclusions: Black discoloration of the thyroid gland has been frequently documented in patients with prior prolonged tetracycline use, classically with minocycline. Given the widespread use of this medication for pulmonary and dermatologic indications, it should be considered whether increased suspicion should be raised for thyroid nodules in patients with this medication history given the association with malignancy.