The Sparing Phenomenon. A case series of the inverse Koebner and related phenomena

Introduction: The sparing of the involvement of a cutaneous disease in a site that has been previously subjected to a skin disease, congenital nevus or physical insult has been reported in literature by various names, including the inverse Koebner phenomenon.Objectives: To review cases that we have seen and to document the reported cases and unify them with a single term, the “Sparing phenomenon”. Materials and Methods: We report four new examples of this phenomenon and performed a PubMed literature search on related search terms and summarized the reported cases.Results: We report four new cases of this phenomenon. An additional 16 reported cases of the sparing phenomenon were identified. Herpes zoster was the most reported inflammatory disease site followed by; skin irradiation was the commonly documented physical insult. Drug reactions and psoriasis were the most common diseases that spare these sites. The time gap between first and second insult was highly variable.Conclusions: We proposed the term “Sparing phenomenon” to describe the skin disease sparing on an area which was previously subjected to skin disease or physical insult. By introducing this new term to the dermatology glossary, it would be easy to collect and analysis to understand the immuno-pathophsiology of this skin reaction described in various names.