Koebner Phenomenon in Psoriasis

The Isomorphic Response

Jan 8, 2009 Hanish Babu

Koebner phenomenon in psoriasis, also known as isomorphic response, refers to the induction of new psoriasis skin lesions following local trauma or injury to the skin.

Koebner phenomenon is named after Dr. Koebner who in the 19th century observed that a patient developed new lesions in areas where his horse bit him.

Superficial trauma to the epidermis alone will not induce the new lesions; injury to the upper part of dermis (papillary dermis) is necessary for the Koebner's to occur. Insult to the skin may be of any kind, e.g. physical (cuts), chemical (burns), mechanical (rubbing), allergic (contact dermatitis) etc.

The following conditions which cause skin trauma or inflammation can cause Koebner phenomenon and act as Psoriasis Triggers:

Physical Trauma Causing Koebner Phenomenon

• Insect Bites
• Cuts
• Bruises
• Scrapes
• Shaving
• Acupuncture
• Burns
• Constant pressure and rubbing
• Sun Burns
• Adhesive Tapes
• Tattoos
• Injections
• Surgical Wounds

Chemical Trauma Causing Koebner Phenomenon

• Chemical burns
• Chemical irritation
• Vaccinations
• Drug Reactions

Biological Trauma (Disease Conditions) Causing Koebner Phenomenon

• Acne
• Dermatitis
• Herpes blisters
• Miliaria
• Lichen planus
• Chickenpox
• Contact dermatitis
• Pityriasis rosea
• Syphilis
• Scabies
• Pruritus
• Leprosy
• Neurodermatitis

There have been many case reports of Koebner phenomenon developing at sites of surgical wounds, sunburn, chickenpox scars, vaccination ulcers and other skin eruptions.

It usually occurs within 7 to 14 days of injury to the dermis, the interval may vary from 3 days to 3 weeks. Koebner phenomenon has also been reported at sites of bites (insects, animals), drug reactions, herpes zoster and skin prick tests.

Studies have shown that about 50% of people with psoriasis experience the Koebner phenomenon. About 10% of psoriasis patients develop a new psoriatic lesion each time the skin is injured. The likelihood of developing the Koebner phenomenon increases when psoriasis skin rashes are already present.

How Does Koebner Phenomenon Cause New Psoriasis Lesions?

It has been postulated that the local trauma may be exposing the surface receptors on the keratinocytes to activated T lymphocytes and other cytokines like TNF-α and triggering the immunological and inflammatory cascade resulting in psoriatic lesions in the injured skin.

Is Koebner Phenomenon Specific to Psoriasis?

No, Koebner phenomenon is not specific to psoriasis only. Here is a list of conditions causing Koebner phenomenon:

• Lichen planus
• Vitiligo
• Warts
• Lichen nitidus
• Keratosis follicularis
• Molluscum contagiosum
• Erythema multiforme
• Pityriasis rubra pilaris
• Reactive perforating collagenosis
• Pyoderma gangrenosum
• Keloids

Infections like warts and molluscum contagiosum showing the Koebner phenomenon mostly do so through auto-inoculation of the viral particles rather than the dermal injury response. All other inflammatory disorders cause koebner phenomenon as a secondary response to the dermal injury. Dermographism seen in urticaria can also be considered a form of Koebner phenomenon.

What is Koebnerization?

Koebnerization means formation of new skin lesions (e.g. psoriasis plaques) following deep skin injury.

How to Avoid Koebnerization?

• Taking care not to cause conscious injury is the first precaution.
• The psoriasis plaques should not be rubbed, scrubbed or picked upon.
• Any injury should be treated fast, so as not to cause any secondary infection or inflammation that could increase the chances of koebnerization
• Patients with scalp psoriasis should avoid removing the scales with sharp combs or nails.
• Patients with viral infections like wart or molluscum should cleanse the local skin injury with spirit and give clean dressing to the wound till it heals so that auto-innoculations can be prevented.

Reference

• Psoriasis, in Rook’s Textbook of Dermatology, 7th Edition, 2004

The copyright of the article Koebner Phenomenon in Psoriasis in General Medicine is owned by Hanish Babu. Permission to republish Koebner Phenomenon in Psoriasis in print or online must be granted by the author in writing.

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