Drug hypersensitivity reactions during hematopoietic stem cell transplantation.

Drugs may elicit a considerable variety of clinical signs, often affecting the skin and the mucous membranes. The most common are maculopapular exanthema, urticaria and angioedema. More rarely pustular, vesiculobullous, vasculitic and lichenoid lesions may be observed. Apart from the morphology, also the chronology of the occurrence and the evolution of the single skin lesions and the exanthema are paramount in the clinical diagnosis. Often, the skin is the only affected organ; however, it may herald a systemic involvement of internal organs, such as in severe drug-induced hypersensitivity syndromes or anaphylaxis. Cutaneous manifestations, particularly maculopapular exanthemas have a high incidence among patients treated with hematopoietic stem cell transplantation. In many cases, a virus- or drug-induced origin or a combination of both is responsible. However, the transplantation itself may also induce similar skin changes. These exanthemas include most often graft-versus-host disease, and rarely engraftment syndrome or eruption of lymphocyte recovery. The elucidation of the underlying cause of the exanthemas occurring in immune compromised patients and the determination of the correct diagnosis remain challenging. An extensive differential diagnosis has to be put forward. This includes several groups of disorders with sometimes very similar cutaneous manifestations. Manifestations form the underlying disease, complications from therapy, infections and drug reactions are the most common differential diagnoses.