Oil dropL60.8

The term "psoriatic oil spot" goes back to the Wroclaw/Tübingen dermatologist HA Gottron.

Psoriatic nail bed change: Reddish to yellow-brown focal point of psoriasis shining through the nail plate, which does not push forward with the growing nail. See also Nail changes in psoriasis vulgaris.

To understand psoriatic onychodystrophies of the distal nail matrix, one must be aware of dichotomous nail growth. Pathologic changes of the distal nail matrix and nail bed may proceed without altering growth and structure of the dorsal nail plate.

Oil spot is rarely encountered in its localized pure form; it usually occurs in combination with other psoriatic nail phenomena. Its development is announced by a circumscribed, rather low-intensity, dark pressure pain. It then becomes visible as an initially reddish, later as a reddish-brown, usually oval, well-bordered spot. Various examiners found a white-blanched mass over which the nail plate is unchanged.

An oil stain may also gradually disappear without displacement. It does not grow out distally with nail growth (unlike spots).

Since the proximal nail matrix is unchanged in a solitary oil spot, due to the dichotomous growth of the nail plate, the superficial, unaffected portion of the nail pushes over the oil spot. An oil spot can grow areally. Its areal progression is indicated by a reddish-brown halo around the oil spot.

Histopathologically, the oil patch represents a subungual psoriatic focus of the distal matrix. Here, the matrix epithelium is acanthotically widened, with papillary capillary dilation, parakeratotic keratinization, Munro microabscesses, and focal erythocyte extravasations between the nail bed and nail plate.

No special therapy required; local therapy is not successful.

A systemic treatment corresponding to the usual systemic treatment of psoriasis vulgaris would be possible. This decision has to be carefully considered also with regard to other psoriatic involvement of the integument.