Central nervous system lymphoma and neurolymphomatosis in equids

Lymphoma affecting the central and peripheral nervous systems in equids is rarely reported.

To describe the clinical presentation, neuroanatomical localization, laboratory and pathologic features, type of lymphoma, and outcome to further current knowledge.

Fourteen equids (13 horses, 1 mule).

Retrospective study. Medical records from a veterinary teaching hospital were reviewed (1993-2025). The inclusion criteria consisted of a definitive diagnosis of lymphoma of the nervous system. Data collected included signalment, neurologic findings, laboratory results, imaging, cerebrospinal fluid (CSF) analysis, immunophenotyping, and necropsy examination. Descriptive statistics were used.

Nervous system lymphoma, either primary or concurrent with multicentric lymphoma, accounted for 11.6% of lymphoma cases. Multifocal neurologic disease was the most common presentation. Common hematologic findings included leukocytosis with neutrophilia, normal plasma fibrinogen concentration, high neutrophil-to-lymphocyte and red cell distribution width-to-platelet ratios, and hypocalcemia. Cytology of the CSF provided a definitive diagnosis in 56% of sampled cases. Prognosis was poor with a median survival time of 4.5 days from diagnosis. All lymphomas were of B-cell origin, including diffuse large B-cell lymphoma, small lymphocytic lymphoma, and T-cell-rich large B-cell lymphoma.

Nervous system lymphoma in equids might be more common than previously reported. Primary nervous system small lymphocytic B-cell lymphoma in a horse and multifocal nervous system lymphoma in a mule have not been reported previously. Analysis of CSF is useful in the antemortem diagnosis of central nervous system lymphoma. Neurologic examination, CSF analysis, and necropsy should be routinely performed in cases of multicentric lymphoma to rule out neurologic involvement.