Additional stains and immunohistochemistry: what else can the pathologist tell us?

Abstract

Background: For the veterinary pathologist, the ‘bread and butter’ of our work is the tissue slide stained with haematoxylin and eosin (H&E). This has long become globally recognised as the ‘standard’ stain, with haematoxylin highlighting the nuclei of cells dark blue and eosin staining the cytoplasm pink. With experience, the pathologist can recognise and interpret many subtle changes in intensity, saturation and distribution of staining with H&E for example, histopathological changes of degeneration or necrosis within cells can be identified and reported with H&E alone. Indeed, H&E is perhaps underappreciated as a highly valuable tool by pathologists and clinicians alike. The vast majority of routine cases, particularly those that are non-neoplastic or of infectious aetiology, will not require more than H&E staining for making a complete histopathological diagnosis; however, there are times when microscopic changes or structures, recognised on H&E, either cannot be definitively diagnosed without an additional stain or, considering the clinical history and possible differentials, may be missed without one or more additional stains. Aim of the article: This article discusses the veterinary pathologist's approach to using special histochemical stains and immunohistochemistry to reach or confirm a histopathological diagnosis. It covers some of the common stains and antibodies and how and when they might be used.