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Onychocytic Matricoma: A New, Important Nail-Unit Tumor Mistaken for a Foreign Body

Karolyn A. Wanat, MD1; Erika Reid, MD1; Adam I. Rubin, MD1
[+] Author Affiliations
1Department of Dermatology at the Hospital of the University of Pennsylvania, Philadelphia
JAMA Dermatol. 2014;150(3):335-337. doi:10.1001/jamadermatol.2013.6358.
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Onychocytic matricoma (OCM) is a benign acanthoma of the nail unit that presents with localized thickening of the nail plate and melanonychia.1 This newly described entity has suggestive clinical features and distinctive histopathologic changes.

Article InformationCorresponding Author: Adam I. Rubin, MD, Department of Dermatology, Hospital of the University of Pennsylvania, 3600 Spruce St, 2 Maloney, Philadelphia, PA 19104 (Adam.Rubin@uphs.upenn.edu).

Published Online: February 5, 2014. doi:10.1001/jamadermatol.2013.6358.

Conflict of Interest Disclosures: None reported.

Additional Information: Dr Wanat is now with the Department of Dermatology, University of Iowa, Iowa City.

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Figure 1.
Clinical and Dermatoscopic Findings

A, On the right second digit, there was a black longitudinal streak that involved almost the entire length of the nail unit, but stopped at the proximal nail fold. B, Localized nail-plate thickening also was observed. C, Dermatoscopic findings highlighted the pigmentation. D, The localized thickening simulated a foreign body.

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Figure 2.
Histopathologic Findings

Excisional biopsy highlighted a proliferation of the nail matrix epithelium with pigmented cells and a thickened keratogenous zone on high power (hematoxylin-eosin, original magnification ×200).

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