P24 immunohistochemistry on lymphoid tissue: the histopathologist's role in HIV diagnosis

Pathology of infectious diseases: what does the future hold?

The demand for expertise in pathology for the diagnosis of infectious diseases (ID) is continually growing, due to an increase in ID in immunocompromised patients and in the (re)-emergence of common and uncommon diseases, including tropical infections and infections with newly identified microbes. The microbiology laboratory plays a crucial role in diagnosing infections, identifying the responsible infectious agents and establishing sensitivity of pathogens to drug therapy. Pathology, however, is the only way to correlate the presence of an infectious agent with the reaction it evokes at cell and tissue level. For pathologists working in the field of ID pathology, it is essential to dispose of competence in cell and tissue pathology as well as in microbiology. Expertise in ID includes understanding of taxonomy and classification of pathogens as well as morphological criteria supporting their identification. Moreover, ID pathologists must master the methods used to detect pathogens in fixed cell and tissue samples, notably immunohistochemistry, in situ hybridization and the polymerase chain reaction. Paradoxically, the increasing frequency of lesions caused by pathogens and diagnosed in a pathology laboratory appears to be paralleled by a gradual loss of expertise of pathologists in the field of infectious and tropical diseases. We contend that this may be due at least in part to the continuously increasing number of samples of tumor tissue pathologists deal with and the rapidly expanding number of tissue based biomarkers with predictive value for new anti-cancer therapies. In this review, we highlight current and future issues pertaining to ID pathology, in order to increase awareness of its importance for surgical and molecular pathology. The intention is to contribute to the development of best practice in ID pathology.

Surgical Pathologic Diagnosis

Surgical pathology results can play a crucial role in the management of immunocompromised patients. Here we highlight factors that differ between immunocompromised and immunocompetent hosts, such as variation in inflammatory response. Conditions that are covered include drug reactions, disease within solid organ allografts, immune reconstitution inflammatory syndrome, specific immunodeficiency syndromes, neoplasms related to viral infections, and viral, bacterial, fungal, and parasitic infections. Special techniques including immunohistochemistry, in situ hybridization and molecular detection of pathogen nucleic acid from formalin-fixed, paraffin-embedded tissue are discussed.

[What place and what future for the pathology of infectious and tropical diseases in France?]

The management of tissues and cellular samples by the pathologists in the infectious and tropical diseases pathology field in 2014 needs a strong knowledge of both morphological and molecular domains which includes the good control: (i) of the taxonomy of infectious and tropical diseases pathology leading to the pathogens identification and (ii) of the ancillary methods which can be used in fixed samples in order to detect or better identify these pathogens. There is a recent paradox in France concerning the frequency of infectious diseases to be diagnosed in pathology laboratories and the progressive loss of pathologist's expertise in this domain. Different reasons could explain this statement including the omnipresence of the tumour lesions to be managed in a pathology laboratory as well as the recent constraints associated with the different biomarkers that are mandatory to be detected by immunohistochemistry and/or by molecular biology. Even if the microbiologists play a pivotal role for identifying the different pathogens as well as for the assessment of their sensitivity to the anti-microbial drugs, a large number of infectious diseases can be diagnosed only on fixed tissue and/or cells by the pathologists. The purpose of this review is to describe the current and future issues of infectious and tropical diseases diagnoses in pathology laboratories, in particular in France.

The incidence of human herpes virus-8 expression in lymph node biopsies from human immunodeficiency virus-positive patients

AIMS

Human immunodeficiency virus (HIV)-related lymphadenopathy is characterized by a wide spectrum of histological changes. Three patterns have been described which correspond to clinical stages of HIV/acquired immune deficiency syndrome (AIDS). Castleman disease is a heterogeneous group of disorders. A recently described variant, multicentric Castleman disease (MCD), of which some cases are associated with human herpes virus-8 (HHV-8), has been reported in both HIV-seropositive and -negative patients. Considerable morphological overlap occurs between one of the patterns of HIV lymphadenopathy and this variant.

METHODS AND RESULTS

This retrospective histopathological study on 95 cases of HIV-reactive lymphadenopathy assessed the incidence of the different patterns and HHV-8 on immunohistochemistry (IHC). Of the 95 cases, 78 (82.1%) were HHV-8-negative, of which 46 (59.0%) were classified as pattern A, 20 (25.6%) as pattern B and 12 (15.4%) as pattern C. Nine (31.0%) of 29 cases with pattern B and 8 (40.0%) of 20 cases with pattern C were HHV-8 positive. In total 15 cases of MCD were diagnosed in this series.

CONCLUSION

This study draws attention to the overlap between HIV lymphadenopathy and MCD. We recommend that cases of HHV-8-associated MCD should be investigated for HIV infection.