Thyroid gland
Miscellaneous non-neoplastic disorders
Black / pigmented thyroid

Author: Andrey Bychkov, M.D., Ph.D. (see Authors page)

Revised: 25 January 2017, last major update June 2015

Copyright: (c) 2015-2017,, Inc.

PubMed Search: black thyroid
Cite this page: Black / pigmented thyroid. website. Accessed March 18th, 2018.
Definition / general
  • Rare side effect of minocycline therapy, ~ 100 cases reported
  • Pigment deposition in thyroid gland in patients on minocycline (often prescribed for chronic acne) or related tetracyclines
  • Pigment also deposited in bone, teeth, skin, nails and oral mucosa (Diagn Cytopathol 1991;7:640)
  • Pigment may be lipofuscin, melanin / neuromelanin or an oxidation product of minocycline; however, lipofuscin is a predominant fraction (Diagn Cytopathol 2006;34:106)
  • Thyroid discoloration (dark red tissue) may also be due to psychotropic drugs such as doxepin, lithium carbonate or tricyclic antidepressants (Arch Pathol Lab Med 1994;118:79)
Clinical features
Case reports
Gross description
  • Normal size, uniformly dark brown to jet black on surface and on cut section
  • Coexisting tumor tissue, if present, is frequently hypopigmented compared to rest of the gland, due to altered function of thyroid peroxidase in neoplastic cells
Gross images

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Thyroid gland with black pigment

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Black thyroid and follicular adenoma

Cut surface

Coal black coloration

Microscopic (histologic) description
Microscopic (histologic) images

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Minocycline induced pigmentation,
contributed by Dr. Mark R. Wick

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Pigmented cells and colloid


Fig 1: nodule uninvolved by pigmentation represents carcinoma
Fig 2: tumor (no pigment) and pigmented nontumorous follicles (arrow)
Fig 3: pigmented follicular epithelial cells and macrophages
Fig 4: pigment is negative for iron stain

Cytology description
  • Dark brown, finely granular intracytoplasmic pigment in follicular cells and macrophages on Papanicolaou stain
  • Small round granules are darker and more regular in size and shape than hemosiderin
  • On Diff-Quik stain, granules are dark blue (Diagn Cytopathol 2010;38:579)
  • Often no specific findings when FNA is done for a thyroid nodule - neoplasms likely do not contain pigment (Diagn Cytopathol 2007;35:135)
Positive stains
Negative stains
Electron microscopy description
  • Numerous electron dense granular structures in lysosomes, with leakage into cytoplasm and exocytosis into follicular lumina
Electron microscopy images

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Pigment granules in cytoplasm and colloid space

Pigment deposits and Xray spectrogram

Experimental black thyroid, dog

Experimental black thyroid, monkey

Differential diagnosis