Seborrheic (Seborrhoeic) Keratoses of the Nailbed

Ungual seborrheic keratosis.

Bon-Mardion M, Poulalhon N, Balme B, Thomas L.

J Eur Acad Dermatol Venereol. 2010 Sep;24(9):1102-4.

Seborrheic (seborrhoeic) keratosis (SK) is seen almost daily by dermatologists and is the most common benign tumour (whether it be in the skin or not).

It is a brownish “stuck on papule” initially smooth becoming darker and rough-feeling with time. It can be located anywhere on the body where hair follicles are present (therefore sparing the palms and soles).

Practically, its interest lies not in its pathogenesis but in its differential diagnosis. Pigmented lesions such as malignant melanoma need to be ruled out, often requiring a biospy.

This article from Lyon, France shows just how ubiquitous SK are, including the nailbed. The diagnosis of SK was histologicaly confirmed after displaying compatible dermoscopical features.

Even is this case is of a stable white yellowish nail (leukoxanthonychia) and that the differential diagnosis includes squamous cell carcinoma, onychomatricoma and onychopapilloma (HPV induced) it is important to keep in mind that for physicians not used to seeing nail conditions the differential diagnosis should also include pigmented lesions.

It is also possible that SK presents as longitudinal melanonychia: it can be due to a melanocytic nevus, a malignant melanoma, trauma and now even a SK !

It is quite surprising there are not more reports of SK on the nailbed, but after all there are no hair follicles in the nailbed.

In practice though, it doesn’t change the importance of doing a nail biopsy in a longitudinal discoloration of the nail (brown, yellow, white) (after having excluded a fungal infection), to exclude in case of doubt a malignancy.