Categorization of and comments on isomorphic and isotopic skin reactions

Reverse Koebner phenomenon in erythema nodosum leprosum

BACKGROUND

Erythema nodosum leprosum (ENL) is an immunologically mediated phenomenon complicating the course of leprosy. Reverse Koebner phenomenon is the term used to describe the sparing of previously injured or diseased skin by new skin lesions of the disease.

METHODS

A middle-aged woman with a known case of lepromatous leprosy for the past year presented with an eruption of reddish painful nodules over her body. The lesions were found to characteristically spare the sites of previous scars.

RESULTS

This sparing phenomenon of previous scar sites has been termed reverse Koebner phenomenon, a site of the body that offers greater resistance than the rest of the body to the onset of the disease, seen in various diseases, but it has never been described in ENL.

CONCLUSION

This sparing of scar sites in ENL can be attributed to reverse Koebner phenomenon.

Skin manifestations in patients with coronavirus disease 2019

PURPOSE OF REVIEW

Coronavirus disease 2019 (COVID-19) is a well established respiratory tract illness. Recent studies in adults and children have shown an increasing number of patients reporting polymorphic cutaneous manifestations during COVID-19, including different types of rashes, from maculopapular, vascular, vesicular to atypical forms.

RECENT FINDINGS

Although pathogenesis of skin manifestations is still not fully understood, it has been proposed that cutaneous involvement during COVID-19 may be the results of the activation of the immune response against severe acute respiratory syndrome coronavirus-2, the reactivation or co-infection of herpesviruses or drug hypersensitivity.

SUMMARY

According to available literature, skin manifestations in patients with COVID-19 may be categorized on the basis of their clinical presentations as follows: erythematous rashes, lesions of vascular origin, vesicular rash, urticarial rash and acute generalized exanthematous pustulosis (AGEP), erythema multiforme and other polymorphic erythema/atypical reactions. Prompt recognition of these cutaneous manifestations represents a crucial point to facilitate diagnosis and management of COVID-19 patients.

Synthesis of the Data on COVID-19 Skin Manifestations: Underlying Mechanisms and Potential Outcomes

The incidence of coronavirus disease 2019 (COVID-19)-related skin manifestations has progressively grown, in parallel with the global severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spreading. The available evidence indicates that cutaneous signs are heterogeneous and can be divided as follows: a) erythematous rashes, b) lesions of vascular origin, c) vesicular rashes, d) urticarial rashes, and e) acute generalized exanthematous pustulosis (AGEP), erythema multiforme (EM) and other polymorphic/atypical reactions. Most cutaneous manifestations appear simultaneously or after respiratory and/or systemic symptoms such as fever, even if rarely urticaria has been reported as the first sign of the disease. It has been proposed that erythematous and vesicular rashes, as well as urticaria, are the result of immunological activation against Sars-CoV-2, similarly to other viral exanthems; alternatively, reactivation or co-infection of herpesviruses and drug hypersensitivity represent possible etiologic diagnosis that has to be considered. Regarding lesions of vascular origin, ischemic ones are the result of systemic hypercoagulability established in severe infections, whereas chilblains seem to be linked to the type I-interferon massively produced to halt virus replication. AGEP is triggered by drugs, whereas EM could represent a delayed immune response to the virus or a hypersensitivity reaction to drugs elicited by the inflammatory process built to fight the infection. A further pathogenic hypothesis is that the virus, or its particles detected in the skin (particularly in endothelium and eccrine glands), could be responsible for certain skin reactions, including chilblains and EM. From the available data, it appears that chilblains are correlated with younger age and less severe disease, while ischemic manifestations occur in the elderly with severe infection. In conclusion, larger studies are needed to confirm the suggested pathogenetic mechanisms of COVID-19-related skin reactions and to determine the potential prognostic significance of each one.

A case of bullous pemphigoid showing antigenic competition-like phenomenon

Antigenic competition in the skin is a phenomenon in which the current dermatitis is distributed away from the area of previously existing dermatitis. Bullous pemphigoid may present such phenomenon, even if the responsible antigen was the same.

Immunocompromised cutaneous district, isotopic, and isopathic phenomena-Systematic review

BACKGROUND

Although the development of lesions in skin areas that have undergone injury has long been known, understanding of its pathogenesis is limited. Depending on their peculiarities, those events have been described as isomorphic, reverse isomorphic, pseudoisomorphic, isotopic, and isopathic phenomena. Ruocco's immunocompromised cutaneous district (ICD) concept was proposed to include all those phenomena.

AIMS

We performed a systematic review and critically evaluated the current understanding about ICD and its relationship with the isotopic and isopathic phenomena.

METHODS

To illustrate the complexity of the theme, we present a case of subclinical leprosy, whose manifestation was brisk in an old tattoo. The possible interaction between the approached phenomena, acting in the genesis of the disease, made this a pertinent study. The research was conducted under the PRISMA-P guidelines, in seven biomedical databases between 1996 and 2018. The eligibility criteria were systematic reviews, meta-analyses, clinical studies, and case series, written in English, French, Italian, Portuguese, or Spanish.

RESULTS

Using standardized keywords, 1220 articles were identified. After applying the eligibility criteria, 53 studies were selected.

CONCLUSION

This review ratifies that all these phenomena are aspects of one single condition. They can be integrated into the ICD concept with the pathogenesis including: (a) neural damage (peripheral or central) and (b) chronic lymphedema. Both may change the local neuroimmune interaction. The identification of these phenomena and the understanding of their pathogenesis are of paramount importance, to define the diagnosis and choose the therapeutic strategy.

Koebner's sheep in Wolf's clothing: does the isotopic response exist as a distinct phenomenon?

Until 1995, a case of psoriasis developing within the dermatome of a healed herpes zoster was taken as a Koebner phenomenon. In this year, however, the term 'isotopic response' was introduced by Wolf et al. to describe 'the occurrence of a new skin disorder at the site of another, unrelated and already healed skin disease', thus appearing 'on apparently unaffected and healthy skin'. Initially, the term was mainly related to herpes zoster, but today the name 'Wolf's isotopic response' is used to include a plethora of other triggering factors such as healed cutaneous leishmaniasis, tinea or varicella. For obvious reasons, such triggering factors cannot be taken as examples of 'unaffected and healthy skin'. Notably, the authors themselves have categorized the dermatome of a healed herpes zoster as a 'vulnerable area'. In a recent commentary, Wolf et al. have expanded the definition of healed skin diseases triggering an 'isotopic response'. They now included 'scars, pigment changes, color changes or various other minimal changes by the first disease'. Hence, there is no clear-cut criterion to distinguish the isotopic response from a Koebner reaction. Wolf et al. even argue that, if the triggered disorder precedes the appearance of generalized skin lesions, then it is not a Koebner reaction but 'Wolf's isotopic response'. In our view, such definition is unacceptable. All reactions of this kind represent examples of a Koebner phenomenon. Accordingly, the 'isotopic response' should today be taken as a historical error.

Mycobacterium tuberculosis found at both skin lesions and Mantoux testing site in a patient with erythema induratum of Bazin

Mycobacterium tuberculosis is very rarely found in erythema induratum of Bazin; recently, we found an unusual case with positive acid‐fast bacilli and polymerase chain reaction for detecting M. tuberculosis in both skin lesions of the extremities and the site of Mantoux test.

Loco-regional immune default: The immunocompromised district in human and comparative dermatology

Lately, the innovative concept of an immunocompromised cutaneous district (ICD) has been introduced to explain why a previously injured cutaneous site may become in time a privileged location for the onset of opportunistic infections, tumors, and immune reactions. The injuring events capable of rendering a skin region a potential ICD are various, numerous, and most of the time identifiable by means of a careful clinical history. The reason that only a small minority of injured skin areas actually becomes ICDs, with subsequent opportunistic localization of a second and unrelated skin disorder, is presently unknown. The ICD is a conceptual entity that is not limited to human dermatology. It can also apply to veterinary medicine. Development of sarcomas at the injection site in cats after routine vaccination and, occasionally, administration of pharmaceutical products, as well as insertion of any foreign body, is a repeatedly documented event. Antigen load, persistent inflammation, and fibroblastic proliferation are thought to be important factors predisposing to the onset of fibrosarcoma in cats. Recently, it has been hypothesized that a local immunosuppression caused by inhalant glucocorticoids may have favored the development of regional demodicosis in cats. In our opinion, injection-site sarcomas and feline localized demodicosis can be considered examples of veterinary ICDs.