Multiparameter flow cytometry in the differential diagnosis of aberrant T-cell clones of unclear significance

Flow immunophenotyping of benign lymph nodes sampled by FNA: Representative with diagnostic pitfalls

Background

Fine‐needle aspiration with flow cytometry (FNA‐FC) is routinely used in the evaluation of lymph nodes suspicious for lymphoma, yet data comparing immunophenotype distributions and outliers in benign lymph nodes sampled by fine‐needle aspiration (FNA) versus excision are lacking.

Methods

Flow cytometry data from 289 benign lymph node FNA cases were assessed for the overall antigen distribution, with a focus on outliers relevant to the diagnosis of lymphoma. Distributions and outlier proportions were compared with those of a separate cohort of 298 excisional biopsies.

Results

Compared with excisional biopsies, FNA specimens overrepresented CD3+ events (72% vs 63%), underrepresented CD19+ events (22% vs 29%), and had 25% fewer large cell–gated events. Normalized antigen distributions in FNA were equivalent to those in excisional biopsy. Twenty‐three percent of FNA‐FC cases exhibited an outlier, including a skewed kappa:lambda light‐chain ratio, increased CD5+ or CD10+ B‐cell events, a skewed CD4:CD8 ratio, and increased CD7 loss on T cells, with no significant differences in frequency or type in comparison with excisional specimens. Outliers for the light‐chain ratio and T‐cell antigens were enriched among older patients and included patients with a variety of autoimmune/rheumatologic conditions.

Conclusions

Benign lymph node FNA yields flow immunophenotypes remarkably similar to those from excisional biopsies. Outlier flow immunophenotypes are identified in benign lymph nodes sampled by FNA at a frequency similar to that with excisional biopsies. Older patients, who have a higher baseline risk of lymphoma, are more likely to exhibit lymphoma‐mimicking outliers such as a light‐chain predominance on B cells and skewed CD4:CD8 ratios or increased CD7 loss on T cells, and they warrant additional diagnostic caution.

Fine‐needle aspiration–based flow cytometry of lymph nodes is comparable to excisional biopsy and exhibits similar outliers. The reference ranges provided in this study can aid pathologists and contribute in the long term to computational flow analysis and biomedical research.

Normative data for flow cytometry immunophenotyping of benign lymph nodes sampled by surgical biopsy

Aims

To create clinically relevant normative flow cytometry data for understudied benign lymph nodes and characterise outliers.

Methods

Clinical, histological and flow cytometry data were collected and distributions summarised for 380 benign lymph node excisional biopsies. Outliers for kappa:lambda light chain ratio, CD10:CD19 coexpression, CD5:CD19 coexpression, CD4:CD8 ratios and CD7 loss were summarised for histological pattern, concomitant diseases and follow-up course.

Results

We generated the largest data set of benign lymph node immunophenotypes by an order of magnitude. B and T cell antigen outliers often had background immunosuppression or inflammatory disease but did not subsequently develop lymphoma.

Conclusions

Diagnostic immunophenotyping data from benign lymph nodes provide normative ranges for clinical use. Outliers raising suspicion for B or T cell lymphoma are not infrequent (26% of benign lymph nodes). Caution is indicated when interpreting outliers in the absence of excisional biopsy or clinical history, particularly in patients with concomitant immunosuppression or inflammatory disease.

Human herpesvirus 6 lymphadenitis in drug rash with eosinophilia and systemic symptoms syndrome: a lymphoma mimic

AIMS

Lymphadenopathy, haematological abnormalities and constitutional symptoms are among the non-specific manifestations seen in drug rash with eosinophilia and systemic symptoms (DRESS), an uncommon but potentially fatal cutaneous adverse drug reaction. The ubiquitous human herpesvirus 6 (HHV-6) plays a unique role in the pathogenesis of DRESS, with emerging data suggesting that reactivation occurs in most cases and contributes to the clinical manifestations, including lymphadenopathy. Further, in the appropriate clinical context, demonstration of HHV-6 reactivation may lend support to a diagnosis of DRESS. The histopathology of DRESS-associated HHV-6 lymphadenitis is reported rarely, with morphologic and immunophenotypic characteristics concerning for T cell lymphoma. The aim is to characterize the histopathology of HHV-6 lymphadenitis in the context of DRESS and to highlight this as an important cause of lymphadenopathy that may be a clinical, morphologic and immunophenotypic mimic of lymphoma.

METHODS AND RESULTS

We describe a case of lymphoma-mimicking lymphadenitis in which the histopathological demonstration of reactivation of HHV-6 infection lent support to the clinical diagnosis of DRESS.

CONCLUSION

Lymph node biopsies concerning for T cell lymphoma should be evaluated for HHV-6 involvement in a clinical context suggestive of DRESS.