Extreme lymphocytosis with myelomonocytic morphology in a horse with diffuse large B‐cell lymphoma

Abstract

An 11-year-old, 443-kg Haflinger mare was presented to the North Carolina State University Veterinary Teaching Hospital with a 2-week history of lethargy and a 3-day duration of anorexia, pyrexia, tachycardia, and ventral edema. Severe pitting edema, peripheral lymphadenopathy, and a caudal abdominal mass were noted on physical examination. An extreme leukocytosis (154.3 × 10 /μL) and microscopic hematologic findings suggestive of myelomonocytic leukemia were observed. Serum protein electrophoresis revealed a monoclonal gammopathy and urine protein electrophoresis revealed a monoclonal light chain proteinuria. Necropsy and histopathology confirmed widespread neoplastic infiltration in many organs with a heterogenous population of cells; there was no apparent evidence of bone marrow involvement. Immunohistochemistry confirmed presence of a majority of B cells with a limited antigen expression, admixed with a lower number of T cells. Molecular clonality analysis of IgH2, IgH3, and kappa-deleting element (KDE, B cell) on whole blood and KDE on infiltrated tissues revealed clonal rearrangements, and the KDE intron clones that amplified in blood and in infiltrated tissue were identical. In contrast, the clonality analysis of T-cell receptor γ revealed no clonality on blood cells and infiltrated tissues. In conjunction with the histopathologic changes, the lesion was interpreted to be composed of neoplastic B cells with a reactive T-cell population. Polymerase chain reaction testing for equine herpes virus 5 was negative. The final diagnosis was diffuse large B-cell lymphoma with a marked hematogenous component.

PCRfor antigen receptor rearrangement (PARR) clonality testing in a horse with a solitary retropharyngeal lymphoma

“…), and has recently been described for lymphoma in horses (Meichner et al . ). Briefly, PARR testing assesses DNA from cells to ascertain if they come from the same cell line, termed monoclonal (typically neoplastic), or from different cell lines, termed polyclonal (typically reactive) (Avery ).…”

“…Additionally, PARR has been used to successfully identify diffuse intermediate to large B cell lymphoma with a robust haematogenous phase (TCRLBCL) in both blood and infiltrative tissue from a horse with multicentric disease (Meichner et al . ). To the authors’ knowledge, this is the first documented use of PARR in equine solitary extranodal lymphoma.…”

PCR for antigen receptor rearrangement (PARR) in equine veterinary medicine

“…), and it has also been used to aid the diagnosis of a diffuse large cell lymphoma (Meichner et al . ) and for characterisation of B cell neoplasms (Badial et al . ).…”

Diagnostic Tools and Dilemmas With Equine Leukemias

“…A significant difference between the case series was the presence of left-shifted neutrophils with toxic change in 1 study, which suggested bone marrow damage; however, this finding was not supported in the current study, as toxicity was rarely noted, a finding that agrees with other reports of equine leukemia. [1][2][3][4][5][6] The rapid release of maturing neutrophils that results in toxicity is typically related to infectious or toxic insults to the bone marrow, but under some conditions, leukemia (especially with severe neutropenia) may result in a similar finding.…”

“…The 1 lymphoid leukemic case that was unclassified as either B or T could have been further evaluated by molecular analysis to determine which population was clonal and which was reactive, as previously demonstrated in a case report. 3,5 Note that a panel of B and T immunomarkers is better than single lineagespecific markers. Furthermore, some cell types require >1 antibody for identification; for example, CD20 and CD79a are often used concurrently to identify B-cell lineage.…”