Isomorphic cutaneous graft-versus-host disease reaction after ultraviolet exposure: clinical, histological and direct immunofluorescence studies of four allo-transplanted patients.

Acute and chronic graft-versus-host disease (GVHD) continues to be a major limitation to successful haematopoietic stem cell transplantation. If experimental studies and clinical observations could partially elucidate the pathophysiology of acute GVHD, the biology of chronic GVHD is still much less well understood.
The aim of this study is to describe a peculiar photoinduced rash which triggered acute and then chronic lesions of GVHD in four allogenic haematopoietic-transplated patients and discuss the possible aetiology and treatment.

Four patients, two children and two adults affected by either mild or severe chronic GVHD,
developed an erythematous rash on sun- or narrow-band ultraviolet B-exposed area, which triggered the onset of acute
lesions of GVHD. Any of the patients presented neither a history of photosensitivity nor circulating autoantibodies nor
urinary/fecal porphyrine. The histopathologic findings were characterized by an interface dermatitis with sparse perivascular infiltrate of
lymphocytes and scattered necrotic keratinocytes, especially in the upper part of epidermis. Direct immunofluorescence
studies excluded lupus-like pattern, revealing nests of fluorescent bodies at the dermal–epidermal junction and in
papillary dermis. This peculiar isomorphic reaction of cutaneous GVHD after sun or narrow-band ultraviolet B exposures is
described, and the possible mechanism involved is discussed. It may represent an interesting model of progression of
chronic GVHD, starting with an acute stage and ending up with chronic clinical and histological findings, especially
considering that there is no animal model that fully replicates all of the features of chronic GVHD in humans.