Lichenoid cutaneous chronic GvHD following Blaschko lines.

Lichenoid chronic GvHD following Blaschko lines is a rare variant of chronic, localized GvHD.Two patterns of distribution of localized chronic GvHD have been reported in the literature: Blaschko-linear and dermatomal; this last one corresponding to the area of previous zoster infection.Sanli et al.3 described a patient who developed lichenoid GvHD after herpes zoster infection involving the right neck, shoulder, chest, and scapular area, corresponding to the C3–C4 dermatomes.
In post-zoster lichenoid GvHD, it has been hypothe- sized that viral proteins could play a role by altering the surface antigenicity of keratinocytes, thus triggering hypersensitivity reactions at these loci minoris resistentiae, as better documented in other dermatoses developed after a previous herpes zoster infection.3,6,7
The linear or whorled distribution following Blaschko lines, as in our case, could be better explained by the unmasking of a genetic mosaicism due to the donor’s lymphocytes and previously tolerated by the patient’s own lymphocytes.8
This hypothesis is also supported by Happle, who emphasizes the Blaschko-linear rather than dermatomalarrangement of localized GvHD and defines this disorder as polygenic, thus suggesting the preferable definition of a superimposed segmental manifestation. This implies that a segmental involvement could precede the appearance of non-segmental lesions, which fortunately did not happen in our reported case.9