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.