Man's Nail 'Splinter' Was Really a Tumor

A long, dark streak under a man's fingernail was not a splinter, as originally thought, but a benign nail tumor. (Image credit: Copyright © (2014) American Medical Association. All rights reserved.)

What a man thought was a splinter under his fingernail turned out to be a tumor instead, according to a new report of the case.

The man, in his 40s, noticed a dark line under his nail after an injury, which he assumed was a splinter. But the mark remained in the same place for three years without changing, the report said.

When the patient eventually sought help at a Pennsylvania hospital, doctors observed that he had a 2-millimeter-wide (0.08 inches), black vertical streak in his nail, along with nail thickening that made it appear as though the man had a foreign object lodged underneath his nail. [14 Oddest Medical Cases]

But a biopsy of the object revealed that the man actually had a benign nail tumor known as onychocytic matricoma.

In this case, the tumor affected the tissue beneath the nail, known as the lunula, said Dr. Doris Day, a dermatologist at Lenox Hill Hospital in New York City, who was not involved in the man's case. The lunula is the whitish, half-moon shaped region at the base of the nail, and is where new nail cells are formed.

Anything that affects the lunula will grow out along the entire nail, Day said.

Nail tumors do not always have color, as this man's tumor did, Day said. But inflammation in the skin — resulting from the tumor itself, or from trauma or other factors — can sometimes cause the pigment-forming cells of the skin (known as melanocytes) to make the dark pigment melanin, Day said.

"Tumors of the nail are more common than people realize," Day said, noting that sometimes, these tumors are mistaken for nail fungus. She added that most of these tumors are benign, but malignant tumors (capable of spreading to other parts of the body), such as melanoma, can also occur in the nail.

If people have questions about their nails, they should see a dermatologist, who can perform an examination and tests to understand what's affecting the nail, Day said.

The man had his tumor removed, and there was no recurrence after a year, according to the report, published online Feb. 5 in the journal JAMA Dermatology.

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Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.