Churg-Strauss syndrome presenting as scar reactivation: histopathologic features and an illustration of 'locus minoris resistentiae'

Appearance of Verruca Over Linear Verrucous Epidermal Nevus - An Example of Locus Minoris Resistentiae: A Report of Three Cases

Locus minoris resistentiae (LMR) is a site of the body that offers lesser resistance than the rest of the body to the onset of disease. It can be congenital or acquired. Areas of cutaneous mosaicism such as epidermal nevi can act as congenital LMR, leading to the development of inflammatory skin conditions or skin tumors on these. The occurrence of an infectious condition such as warts over nevi is rare. We report three cases of verrucous epidermal nevi (VENs) with the development of verrruca overlying the nevus later in life. The three patients had VEN on forehead, preauricular, and presternal area, respectively, since birth, with development of a warty lesion overlying these a few months before presenting to us. Skin biopsy and histopathological examination of the linear verrucous lesion were suggestive of VEN with hyperkeratosis, thickened epidermis, and papillomatosis. There was no evidence of epidermolytic hyperkeratosis or increased sebaceous glands in the dermis. Biopsy of the new warty lesion showed findings of verruca in all the patients. With the above findings, a diagnosis of verruca superimposed on linear VEN was made in all the three cases. The warts were removed by electrofulguration. Several acquired skin disorders, including inflammatory dermatoses, adnexal disorders, and neoplasms, have been shown to occur superimposed on epidermal or sebaceous nevus. Ours is probably the first ever description of a wart occurring on VEN.

Granulomatous dysimmune reactions (sarcoidosis, granuloma annulare, and others) on differently injured skin areas

Granulomatous disorders are chronic cell-mediated immune responses histologically characterized by collections of macrophages, epithelioid cells, and multinucleated giant cells. This disease spectrum often has an infectious origin, but sometimes neither an infective agent nor an inciting antigenic stimulus can be identified. The skin may be a preferential target for these disorders, especially in the areas that have been damaged by various forms of skin injury (eg, herpetic infections, trauma, thermal or solar burns, vaccinations, tattoos). These damaged skin sites frame the new concept of an immunocompromised cutaneous district (ICD), which defines a skin area with acquired immune dysregulation that can pave the way for the local onset of opportunistic disorders, such as infections, tumors, and granulomatous disorders. Sarcoidosis, granuloma annulare (GA), and forms of granulomatous vasculitis, such as Churg-Strauss syndrome (CSS) and Wegener's granulomatosis (WG), are the most common granulomatous disorders that occur in an ICD and may share common pathogenic mechanisms. Recent studies have found clinical and pathologic overlapping features across noninfectious granulomas. Although no unifying etiology exists, the development of granulomatous processes in the ICD has often been reported and the literature contains various hypotheses to explain it: (1) overactive immune response in a previously injured region with or without loss of immune tolerance; (2) overall reduced immune response; (3) retention of an exogeneous antigen or foreign body; (4) altered neural signaling; and (5) a combination of all the aforementioned processes. T helper cells, T regulatory cells, and macrophages, as well as a number of antigenic proteins, have been identified as potential contributing factors. In addition, a genetic predisposition and an intact systemic immune system are both instrumental for the persistence of local granuloma formation in the ICD.

The immunocompromised district in dermatology: A unifying pathogenic view of the regional immune dysregulation

Besides the systemic immune deficiency, a sectorial default in immune control may occur in immunocompetent subjects. This regional immune defect can appear and remain confined to differently damaged skin areas, lately labeled immunocompromised districts (ICDs). An ICD is a skin area more vulnerable than the rest of the body for genetic or acquired reasons. Its vulnerability mainly consists in a local dysregulation of the immune control, which often facilitates (but sometimes hinders) the local onset of immunity-related eruptions or skin disorders. The factors responsible for localized immune dysregulation are multifarious, being represented by chronic lymphatic stasis, herpetic infections, ionizing or ultraviolet (UV) radiations, burns, all sorts of trauma (especially amputation), tattooing, intradermal vaccinations, and others of disparate nature (eg, paralytic stroke, poliomyelitis). Whatever the cause, in time an ICD may become a vulnerable site, prone to developing opportunistic infections, tumors, or dysimmune reactions (often of granulomatous type), strictly confined to the district itself; however, the opposite may also occur with systemic immune disorders or malignancies that selectively spare the district. In any case, the immunologic behavior of an ICD is different from that of the rest of the body. The pathomechanisms involved in this sectorial immune destabilization may reside in locally hampered lymph drainage that hinders the normal trafficking of immunocompetent cells (eg, chronic lymphedema, posttraumatic lymph stasis) or in a damage to sensory nerve fibers that release immunity-related peptides (eg, herpetic infections, carpal tunnel syndrome), or in both conditions (eg, amputation stump, radiation dermatitis). The ICD is a conceptual entity with no definite shape or dimension. It may take an extremely variable form and extent depending on the causative agent, ranging from a minimal area (eg, intradermal vaccination) or a small area (eg, herpes simplex infection), through a wide area (eg, radiotherapy), a bandlike segment (eg, skin mosaicism, herpes zoster infection), or an acral area (eg, carpal tunnel syndrome), up to a whole limb (eg, Stewart-Treves syndrome) or even an entire half body (eg, brain stroke). Varied newly coined terminology can be used to indicate the specific cause each time that it is responsible for a regional immune dysregulation. The advantage of the umbrella term ICD is that it encompasses all the possible causes involved in a local immune destabilization. An ICD may have a congenital or a postnatal origin, and interesting similarities between the two forms exist. An ICD may also take place in patients with a preexisting systemic immune deficiency, thus creating a more vulnerable site in an already vulnerable patient. Identifying a cutaneous ICD in a given patient is an important standpoint for both diagnostic and prevention purposes. This can be proven by the educative clinical examples that are reported here.