Black thyroid.A finding of a black thyroid gland (figure 1) is unusual and disconcerting. Among the possible causes of black thyroid are minocycline-induced pigmentation, hemochromatosis Hemochromatosis Definition Hemochromatosis is an inherited blood disorder that causes the body to retain excessive amounts of iron. This iron overload can lead to serious health consequences, most notably cirrhosis of the liver. , ochronosis, mucoviscidosis mucoviscidosis /mu·co·vis·ci·do·sis/ (mu?ko-vis?i-do´sis) cystic fibrosis. mu·co·vis·ci·do·sis n. See cystic fibrosis. , ceroid storage disease, bruising, and hemorrhage. In addition, medullary medullary /med·ul·lary/ (med´ah-lar?e) 1. pertaining to a medulla. 2. pertaining to bone marrow. 3. pertaining to the spinal cord. thyroid carcinomas have been reported to produce melanin in rare cases. Minocycline, a derivative of tetracycline, can also cause pigmentation in the skin, nails, oral mucosa, teeth, eyes, bones, cardiac valves, coronary vessels, substantia nigra, and atherosclerotic plaques. In the thyroid, minocycline accumulates in the follicular epithelium and colloid in benign, and even hyperplastic tissue as a result of the oxidative interaction between the drug and the enzyme thyroid peroxidase (figure 2). These black pigment deposits remain in epithelial cells for long periods of time. [FIGURE 1 AND 2 OMITTED] Ultrastructurally, pigment (neuromelanin) is confined to lysosomes lysosomes (līs  sōmz),n the self-contained organelles found inside most cells, which contain hydrolytic enzymes that aid in intracellular digestion. . This granular pigment stains like melanin on Fontana-Masson staining; it can also be bleached. In aspiration cytology specimens, the degenerative changes in follicular epithelial ceils found in black thyroid glands can cause nuclear hyperchromatism and chromatin clumping (figure 3). Pigment present in follicular epithelial cells in fine-needle aspirate can also be mistaken for hemosiderin-laden macrophages. It is interesting that thyroid adenomas and carcinomas fail to incorporate black pigment (figure 1). Although the concentration of minocycline-related pigment can interfere with thyroid function, it appears to be unrelated to tumorigenesis tumorigenesis /tu·mor·i·gen·e·sis/ (-jen´e-sis) oncogenesis. tu·mor·i·gen·e·sis n. Formation or production of tumors. . Pigment-containing follicular epithelium has reduced thyroglobulin thyroglobulin /thy·ro·glob·u·lin/ (thi?ro-glob´u-lin) an iodine-containing glycoprotein of high molecular weight, occurring in the colloid of the follicles of the thyroid gland; the iodinated tyrosine moieties of thyroglobulin form the and ubiquitin u·biq·ui·tin n. A polypeptide found in all eukaryotic cells, including plant cells, that participates in a variety of cellular functions including protein degradation. immunoreactivity. Because of the possible antithyroid effects of minocycline, it seems advisable to monitor thyroid function in patients who are on long-term minocycline therapy. [FIGURE 3 OMITTED] Suggested reading Bell CD, Kovacs K, Horvath E, Rotondo F. Histologic, immunohistochemical, and ultrastructural findings in a case of minocycline associated "black thyroid." Endocr Pathol 2001;12:443-51. Keyhani-Rofagha S, Kooner DS, Landas SK, Keyhani M. Black thyroid: A pitfall for aspiration cytology. Diagn Cytopathol 1991;7:640-3. Thompson AD, Pasieka JL, Kneafsey P, DiFrancesco LM. Hypopigmentation hy·po·pig·men·ta·tion n. Diminished pigmentation, especially of the skin. Hypopigmentation A skin condition that occurs when the body has too little melanin, or pigment. of a papillary carcinoma arising in a black thyroid. Mod Pathol 1999;12:1181-5. From the Department of Pathology, Beth Israel Deaconess Medical Center, Boston. |
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