Thyroid Gland, Follicle - Pigment
comment:Thyroid pigmentation can occur as a result of iron and/or lipofuscin deposition in follicular epithelium or colloid. Dark black pigment with resemblance to melanin is seen in rodents and other species following exposure to minocycline, a semisynthetic derivative of tetracycline ( Figure 1 and Figure 2 ). At least 4 chemicals tested by the NTP have caused thyroid pigmentation. Subtle pigmentation can be seen as a background change in both control and treated rats ( Figure 3 and Figure 4 ).
recommendation:Definitive pigment identification is often difficult in histological sections, even with a battery of special stains. Therefore, it is recommended that a diagnosis of pigment (as opposed to diagnosing the type of pigment, e.g., hemosiderin or lipofuscin) is most appropriate. The pathology narrative should describe the morphological features of the pigment. Not all pigments have to be diagnosed, as some are ubiquitous in aging animals or related to some other disease process and not toxicologically meaningful. The pathologist should use his or her judgment in deciding whether or not secondary deposits of pigment are prominent enough to warrant a separate diagnosis.
Greaves P. 2007. Histopathology of Preclinical Toxicity Studies: Interpretation and Relevance in Drug Safety Evaluation, 3rd ed. Academic Press, Amsterdam, 819-839. Abstract: http://www.sciencedirect.com/science/book/9780444527714
Hardisty JF, Boorman GA. 1990. Thyroid gland. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, 519–536. Abstract: http://www.ncbi.nlm.nih.gov/nlmcatalog/9002563
Hardisty JF, Boorman GA. 1999. Thyroid and parathyroid glands. In: Pathology of the Mouse: Reference and Atlas (Maronpot RR, Boorman GA, Gaul BW, eds). Cache River Press, Vienna, IL, 537–554. Abstract: http://www.cacheriverpress.com/books/pathmouse.htm
Tajima K, Miyagawa J, Nakajima H, Shimizu M, Katayama S, Mashita K, Tarui S. 1985. Morphological and biochemical studies on minocycline-induced black thyroid in rats. Toxicol Appl Pharmacol 81:393-400. Abstract: http://www.ncbi.nlm.nih.gov/pubmed/3001973
Ward JM, Stinson SF, Hardisty JF, Cockrell BY, Hayden DW. 1979. Neoplasms and pigmentation of thyroid glands in F344 rats exposed to 2,4-diaminoanisole sulfate, a hair dye component. J Natl Cancer Inst 62:1067-1073. Abstract: http://www.ncbi.nlm.nih.gov/pubmed/285280
Web page last updated on: August 08, 2014