An Unusual Cause of Femoral Nerve Paresis in a Horse: Disseminated B Cell Lymphoma With Plasmacytoid Differentiation and Direct Neuronal Invasion.
Authors: Barton Charlotte K, Hughes Kelly L, Cowan Catharine, Nout-Lomas Yvette S, Nelson Brad B
Journal: Journal of equine veterinary science
Summary
# Editorial Summary A 21-year-old Quarter Horse presented with progressive left hind limb lameness and neurological signs consistent with femoral nerve dysfunction—reduced cranial advancement, shortened stride, and failure of heel ground contact—yet standard diagnostic imaging proved unrevealing. Marked lymphocytosis (69,600 cells/µL, versus the normal range of 1,500–4,000) prompted investigation into haematological causes, leading to a postmortem diagnosis of disseminated B cell lymphoma with plasmacytoid differentiation that had directly infiltrated the femoral nerve and multiple organ systems including the stomach, colon, adrenal gland, mesentery, heart, and meninges. This case represents neurolymphomatosis—a rare manifestation of disseminated lymphoma characterised by neoplastic lymphocyte invasion of peripheral nerves—as the underlying mechanism of peripheral neuropathy, rather than the more typical mechanical or inflammatory aetiologies clinicians typically encounter. Whilst uncommon in equine practice, disseminated lymphoma with direct nerve infiltration warrants consideration in horses presenting with otherwise unexplained peripheral neuropathies, particularly when concurrent haematological abnormalities are documented; awareness of this differential may prompt earlier recognition and appropriate staging investigations before advanced multisystem involvement occurs.
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Practical Takeaways
- •Disseminated lymphoma with direct nerve infiltration (neurolymphomatosis) should be included in the differential diagnosis for horses presenting with peripheral neuropathies and unexplained lameness, particularly when imaging fails to identify a cause
- •Severe lymphocytosis on blood work warrants investigation for systemic lymphoma; this case demonstrates that lymphoma can present atypically as neurological dysfunction rather than obvious systemic signs
- •When lameness investigations including ultrasound and scintigraphy are unrewarding, hematology abnormalities should prompt consideration of neoplastic disease affecting peripheral nerves
Key Findings
- •A 21-year-old Quarter Horse presented with progressive left pelvic limb lameness caused by direct neoplastic lymphocyte infiltration of the femoral nerve
- •Severe lymphocytosis (69,600 cells/µL; reference 1,500-4,000) was identified on complete blood cell count
- •Postmortem examination revealed disseminated B cell lymphoma with plasmacytoid differentiation affecting multiple organs including stomach, colon, adrenal gland, heart, and meninges
- •Histologic examination confirmed intermediate cell size B cell lymphoma directly infiltrating the femoral nerve at the site of focal swelling, representing neurolymphomatosis