A 51-year-old man was diagnosed with promyelocytic acute leukemia and treated by induction therapy with idarubicin and transretinoic acid, followed by a consolidation with mitoxantrone. In 2008 he relapsed and received transretinoic acid and arsenic trioxide therapy; thereafter, he underwent allogeneic transplantation of peripheral blood stem cells (PBSCs) from a sibling donor.
Eighteen months after PBSCs, the patient developed an asymptomatic unilateral eruption (Fig. 1a,b). At the clinical examination, confluent erythematous papules were observed in a whorled configuration following Blaschko lines, involving the whole left part of the trunk (Fig. 1c,d).
At the time of the examination, the patient was in good health with a normal complete blood cell count, metabolic panel, and liver function test. His only medication was prednisone 5 mg every other day.
A 4-mm punch biopsy was taken from the left flank for histopathological examination and revealed an interface dermatitis with a subepidermal, patchy, lymphocytic inflammatory infiltrate, vacuolar changes of the basal layer, melanophages, and scattered dyskeratotic/necrotic cells in the epidermis (Fig. 2a,b).
A diagnosis of lichenoid chronic graft-vs-host disease (GvHD) following Blaschko lines was made, and the patient started treatment with topical steroids (prednicarbate) once daily for four weeks. The erythematous component of the papules healed, and the patient presented with post-inflammatory hyperpigmentation. No further lesions appeared after one year.
GvHD represents a common complication of allogeneic bone marrow/stem cell transplantation, and it is usually divided into an acute and chronic phase, based on clinical and histological features. The skin is one of the most frequently affected target organs, particularly in the chronic stage. Chronic cutaneous GvHD is characterized by lichenoid lesions or sclerodermoid changes, which are usually widespread, but localized forms may also occur.[2, 3]
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. In particular, Freemer et al. and Cohen and Hymes. showed pictures of patients with a Blaschko-linear distribution.[4, 5] Sanli et al. 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 hypothesized 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.
This hypothesis is also supported by Happle, who emphasizes the Blaschko-linear rather than dermatomal arrangement 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.