Histopathological assessment for opportunistic infections in the iatrogenically immunosuppressed

Abstract

The use of medication to alter the normal function of the immune system treads the fine balance between the body’s ability to fend off foreign or aberrant antigens and increased susceptibility to opportunistic infections as well as decreased cancer immunosurveillance. The expanding array of immunosuppressive drugs, targeting specific mediators or pathways in the immune system, has improved patient outcome both for transplantation and autoimmune disease, but opportunistic infections remain a serious risk. Whilst many of these infections are successfully treated without any histopathological input, pathology plays a significant role by excluding mimics of infection, identifying viral, bacterial, fungal and parasitic infection even before their clinical suspicion, and in the diagnosis of malignancy. In a field which spans all pathogens and every organ system, this paper addresses the more commonly encountered organisms at their usual site of infection with emphasis on establishing a diagnosis and highlighting potential diagnostic traps. Malignancy is also discussed, including recently described lymphoproliferative processes. In recent years immune therapy for the treatment of a range of cancers is becoming routine practice. This too is associated with an increased risk of infection which needs to be differentiated from the spectrum of changes seen in immune therapy related disease.