Are you having Koebner phenomenon?
What is the Koebner phenomenon?
The Koebner phenomenon is perhaps one of the most widely known phenomena in dermatology. It was described for the first time in 1872 by Heinrich Koebner, a well-known 19th century dermatologist, who gave it his name. Some of his patients had developed psoriasis on the site of an excoriation (an abrasion of the skin due to scratching), a bite by a horse or a tattoo.
The term is used to describe the response whereby new lesions appear and develop in patients suffering from skin conditions on healthy skin which has suffered a trauma. A trauma to a "normal" area of skin in a patient with psoriasis can hence lead to new lesions that are identical to those caused by the condition. This is why the Koebner phenomenon is also known as an "isomorphic reaction" (meaning a reaction in the same form).
Is the Koebner phenomenon common in psoriasis?
The Koebner phenomenon is associated with several dermatological conditions, and most frequently with psoriasis, lichen planus and vitiligo. People with psoriasis are hence particularly vulnerable, and those with unstable or erythematic psoriasis, characterised by dark red patches all over the body, are especially at risk.
It should be noted that local traumas do not necessarily trigger this response.
The Koebner phenomenon usually appears between 10 and 14 days after a trauma to the skin, but it can appear up to several years afterwards. Other characteristics are that it does not affect any area in particular, appears most commonly in winter and especially affects children.
What traumas can trigger the Koebner phenomenon?
Various traumas can trigger this response. It has been observed at the site of bites by dogs and insects, abrasions, gunshot wounds, lacerations, burns, scars, friction, contact dermatitis, in the area rubbed by the elastic of a sock and also after the skin has been shaved, exfoliated or waxed.
Here is shown a Koebner phenomenon caused by the scratching of a cat:
Here's shown a Koebner phenomenon in a post-operative scar:
The arms of glasses can cause a Koebner response behind the ears. Filing or manicuring the nails can exacerbate psoriasis of the nails. In one case friction by a tennis racket caused a Koebner phenomenon to appear in the right hand palm of a tennis player. Even when someone has psoriatic arthritis, friction by a wedding ring can lead to psoriatic lesions appearing solely on the ring finger.
In the case of palmoplantar psoriasis, lesions due to the Koebner phenomenon may be concentrated on pressure areas, and not be present on the arch of the foot. Sunburn can also lead to psoriasis spreading massively over the body, known as the photo Koebner phenomenon.
Many dermatoses can cause the Koebner phenomenon, including psoriasis, dermatitis, eczema, herpes, lichen planus, chickenpox and vitiligo. Eczema may therefore trigger psoriatic lesions. Finally, an allergic reaction to flu or tuberculosis vaccination, certain drugs, hair spray or hair dye, a tattoo, urticaria and some therapies such as UV therapy can also lead to a Koebner response.
Here is a picture of a Koebner phenomenon after sun exposure:
Doctors sometimes talk about a reverse Koebner phenomenon when a psoriatic plaque clears after a trauma as may occur after rubella, a cold, acute pharyngitis or an operation.
Although external occurrences of the Koebner phenomenon are most well known, it can also be invisible and located on a nerve in close proximity with the site of an eruption. For example, a wrist fracture or isolated arthrosis can lead to psoriatic lesions on the nails. This is known as a deep Koebner phenomenon which is a rare phenomenon that should not be ignored.
What precautions can be taken?
You should avoid disturbing scale and scratching plaques and, as far as possible, try to avoid friction and minor trauma. Care should be taken when combing or brushing the hair and shaving. Nails should be cut short and not filed. You should limit exposure to the sun, and use sunscreen and hypoallergenic skin care products to avoid any irritation. These should be applied carefully.
If the doctor diagnoses a Koebner phenomenon, any physical or chemical irritant, laser treatments and surgical operations should be avoided. Treatment should be sought as soon as possible in order to maximise its effectiveness.
- Psoriatic lesions may appear on traumatised areas of the skin. This is known as the Koebner phenomenon.
- Various types of trauma can trigger the Koebner phenomenon, including friction, sunburn and tattoos.
- The Koebner phenomenon aggravates psoriasis.
- Le psoriasis en médecine générale, edited by M. Le Maître, published by Arnette
- The isomorphic phenomenon of Koebner, Thappa Devinder Mohan, Indian Journal of Dermatology, Venereology and Leprology, 2004
With thanks to Dr Patrick Brun, dermatologist attached to Cannes University Hospital.