Thyroid & parathyroid

Other thyroid nonneoplastic

Black / pigmented thyroid

Topic Completed: 1 June 2015

Minor changes: 31 December 2020

Copyright: 2015-2021,, Inc.

PubMed Search: black thyroid

Andrey Bychkov, M.D., Ph.D.
Page views in 2020: 1,652
Page views in 2021 to date: 1,153
Cite this page: Bychkov A. Black / pigmented thyroid. website. Accessed December 3rd, 2021.
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

Case #98

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

Contributed by Andrey Bychkov, M.D., Ph.D., Mark R. Wick M.D.

Perinuclear brown pigment

Minocycline induced pigmentation

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Pigmented cells and colloid


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
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