Anyone who has studied dermatology will have come across the term Koebner phenomenon (KP). It is an effect characterised by the appearance of new lesions in patients with active skin disease on previously unaffected skin, secondary to trauma. It is also termed the “isomorphic reaction” - “Iso” – meaning the same, “morphic” - meaning shape, referring to the new lesions appearing after the trauma being identical in form to the original disease.
Latterly, clinicians have expanded the definition to include both physical and damage from many other forms of skin insults (including burns, friction, radiotherapy, laser treatment, tattoos, burns, surgical scars and even surgical mask wearing (1)).
The term pseudo-koebnerisation was added later and is used to describe the spread of an infection in an area of traumatised skin. For example, the spread of a wart as it seeds itself along a scratch on the skin. Reverse Koebnerisation is the opposite – where existing skin lesions disappear following trauma (2, 3) and is much rarer.
Wolf’s isotopic response is like KP but not quite the same. It was first discussed in 1995 (4) and describes a describes the appearance of an altogether different skin disease at the site of an already healed skin disease or lesion.
Heinrich Koebner
Who was Koebner?
KP was named after Heinrich Koebner (Köbner) [1838-1904] who was German dermatologist trained in Berlin and Breslau, and latterly became head of the Breslau School of Dermatology and a professor at the University of Breslau. During his career he made many contributions researching psoriasis, mycosis fungoides, leprosy, syphilis and drug eruptions(5). He was also the first to describe the genetic blistering disorder epidermolysis bullosa. He first described the isomorphic response in a paper in 1872 demonstrating the effect in patients with psoriasis after horse bites, tattoos and wounding (5). The paper was finally published 4 years later.
The Phenomenon
Psoriasis perhaps typifies classic KP. When a patient has active disease, trauma to unaffected (non-lesional) skin usually results in new lesions appearing there within 14 days of the injury. Around 75% of patients with psoriasis will develop koebnerisation at some point in their disease. As well as physical trauma, sunburn can have a similar effect in patients with psoriasis. Vitiligo and Lichen planus are two other diseases which frequently exhibit the effect. There are other diseases which exhibit koebnerisation (see table 1).
Table 1: Selected skin conditions which may exhibit KP or Pseudo-KP
Interestingly, KP tends to arise more readily in areas of the body with repeated friction or pressure where other areas like the scalp and palm are less often affected. KP has been categorised into 4 grades of severity (6):
1. Maximum - KP that develops throughout the trauma site,
2. Minimum - KP that appears as small foci in the trauma area
3. Abortive KP wherein the secondary lesions initially appear as primary lesions but subside naturally within 12–20 days and
4. Lack of response indicating normalization of the trauma site.
Various theories have been put forward to explain KP including immunological disorders and enhanced oxidative stress but there is currently no consensus.
References
1. Mutalik SD, Inamdar AC. Mask-induced psoriasis lesions as Köebner phenomenon during COVID-19 pandemic. Dermatol Ther. 2020;33(6):e14323.
2. Panta P, Andhavarapu A, Sarode SC, Sarode G, Patil S. Reverse Koebnerization in a linear oral lichenoid lesion: A case report. Clin Pract. 2019;9(2):1144.
3. Mohapatra L, Samal K, Mohanty P, Dash S. Reverse Koebner Phenomenon in Bullous Pemphigoid - A Case Report. Indian dermatology online journal. 2019;10(6):692-4.
4. Wolf R, Wolf D, Ruocco V, Ruocco E. Wolf's isotopic response: The first attempt to introduce the concept of vulnerable areas in dermatology. Clin Dermatol. 2014;32(5):557-60.
5. Diani M, Cozzi C, Altomare G. Heinrich Koebner and His Phenomenon. JAMA Dermatology. 2016;152(8):919-.
6. Sagi L, Trau H. The Koebner phenomenon. Clin Dermatol. 2011;29(2):231-6.