Central nervous system lymphoma and neurolymphomatosis in equids.

CSF cytology is essential for antemortem diagnosis of equine CNS lymphoma, which carries a grave prognosis.

This retrospective study from a veterinary teaching hospital (1993–2025) characterizes central nervous system (CNS) lymphoma and neurolymphomatosis in 14 equids (13 horses, 1 mule), representing 11.6% of all lymphoma cases at the institution. Multifocal neurologic disease was the predominant clinical presentation. Key hematologic findings included leukocytosis with neutrophilia, normal plasma fibrinogen, elevated neutrophil-to-lymphocyte ratio, elevated red cell distribution width-to-platelet ratio, and hypocalcemia. CSF cytology yielded a definitive antemortem diagnosis in 56% of sampled cases, underscoring its diagnostic utility. Prognosis was grave, with a median survival of only 4.5 days from diagnosis. All lymphomas identified were of B-cell origin, encompassing diffuse large B-cell lymphoma (DLBCL), small lymphocytic lymphoma (SLL), and T-cell-rich large B-cell lymphoma (TRLBCL). Notable firsts include the description of primary CNS small lymphocytic B-cell lymphoma in a horse and multifocal CNS lymphoma in a mule. The authors advocate for routine neurologic examination, CSF analysis, and necropsy in equids with multicentric lymphoma to detect neurologic involvement. This study expands understanding of an underrecognized condition and highlights that nervous system lymphoma in equids may be more prevalent than previously appreciated, with CSF analysis serving as a critical diagnostic tool in clinical practice.

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