Pseudo-Hutchinson Sign
Author: Sophie Godinho Ramos
Chief Editor: Dr Daniel Keith
What is a pseudo-Hutchinson sign?
Black pigmentation of the nail plate and proximal nail fold due to a benign cause, for example fungal infections, subungual hematomas or benign neoplasms.
It is called a pseudo-Hutchinson sign because it can mimic a Hutchinson sign, which also displays black pigmentation of the nail plate and proximal nail fold, but is associated with malignant melanoma only.
A bit on terminology:
Some of these terms are similar, but they differentiate between causes of the nail change.
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Hutchinson sign: black pigmentation of the nail plate and proximal nail fold caused by malignant melanoma.
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Pseudo-Hutchinson sign: black pigmentation of the nail plate and proximal nail fold due to a benign cause, commonly trauma.
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Pseudo-pseudo-Hutchinson sign: discoloration of the nail plate and proximal nail fold that is not black, for example: red discolouration in a subungual hematoma, or green discolouration in pseudomonas infections.
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Melanonychia: black pigmentation of a nail. It is caused by melanocyte activation or hyperplasia, or by blood under the nail.
Macroscopic Appearance
Irregular black/grey discolouration of the nail plate and entire proximal nail fold, in this case caused by trauma to the nail.
The sudden onset of melanonychia following recent trauma to the nail is consistent with a pseudo-Hutchinson sign.
Weeks later, the discolouration of the nail plate and proximal nail fold has moved with nail growth, revealing a normal section of the proximal nail fold.
Dermoscopic Appearance
Dermoscopy can help identify whether the proximal nail fold is also discoloured.
Black/grey discolouration of the proximal nail fold can clearly be seen in addition to melanonychia.
Again, weeks after the trauma to the nail, a section of healthy proximal nail fold can be seen.
Note: True Hutchinson signs, which are associated with malignant melanomas, almost always present as longitudinal bands extending from the proximal nail fold to the free nail edge. Transverse melanonychia is rare and therefore might be more suggestive of a pseudo-Hutchinson sign.
Sources:
https://dermnetnz.org/topics/melanoma-of-the-nail-unit
https://dermnetnz.org/cme/dermoscopy-course/dermoscopy-of-the-nails
Cohen, P.R., 2024. Trauma-associated pseudo-Hutchinson sign: an autobiographical case report emphasising conditions, pseudo-conditions, and pseudo-pseudo-conditions. Cureus, 16(12).