The pathogenesis of the postherpetic isotopic response remains unknown, but several mechanisms have been proposed. Some authors have suggested that postzoster dermatoses may represent isomorphic response of Köbner phenomenon.13,15 Although isomorphic and isotopic responses share some similarities, these terms describe 2 different phenomena: the first refers to the appearance of the same cutaneous disorder at a different site favored by trauma, while the second manifests a new and unrelated disease at the same location.38 Local anatomic changes such as altered microcirculation, collagen rearrangement, and an imperfect skin barrier may promote a prolonged local inflammatory response. Moreover, the destruction of nerve fibers by the varicella-zoster virus may indirectly influence the local immune system through the release of specific neuropeptides in the skin.39 It has been speculated that some secondary reactions may be the result of type III and type IV hypersensitivity reactions40 to viral antigens or to tissue antigens modified by the virus, inducing either immune hypersensitivity or local immune suppression.41 Some authors have documented the presence of varicella-zoster DNA within early postzoster lesions6,7 by using polymerase chain reaction in early lesions but not in late-stage and residual lesions.12,22 Nikkels et al42 studied early granulomatous lesions by immunohistochemistry and in situ hybridization techniques and concluded that major viral envelope glycoproteins (glycoproteins I and II) rather than complete viral particles could be responsible for delayed-type hypersensitivity reactions. All these findings suggest that secondary reactions presenting on HZ scars are mainly the result of atypical immune reactions to local antigenic stimuli.
The pathogenesis of our case is unknown. From a theoretical point of view, it is possible that varicella-zoster virus may induce fibroblastic proliferation and mucin production on HZ scars; however, if HZ is a frequent process and the virus may induce mucin production, then focal dermal mucinosis in an HZ scar should be a common finding. In our patient, there was no associated disease favoring the development of the cutaneous mucinosis. These localized variants of primary cutaneous mucinosis usually do not require therapy, and a wait-and-see approach is recommended. Topical applications of corticosteroids, pimecrolimus, or tacrolimus, as well as oral isotretinoin, may have some benefit,43 but spontaneous resolution may occur.44 In our patient, topical corticosteroids were applied 2 months following initial presentation without any benefit and the cutaneous lesions gradually improved without any therapy during the subsequent 6 months. Focal dermal mucinosis should be added to the list of cutaneous reactions that may develop in HZ scars.