3.0 Discussion
Lymphoma affecting the spinal cord, meninges, or vertebrae is reported to be a rare cause of ataxia in the horse (Morrison et al. 2008). The colt presented in this case report is younger than the typical 4–10-year-old age range often diagnosed with multicentric lymphoma (Taintor and Schleis 2011). He was examined by a veterinarian nine days prior to presentation and no neurologic deficits were noted at that time, thus the ataxia was acute and had progressed significantly by the time of presentation. An antemortem diagnosis of lymphoma was not obtained in this horse. For safety reasons the neurologic examination was not completed and the horse was humanely euthanized. Gross examination of the spinal vertebrae revealed changes in the articular facets multifocally was consistent with a diagnosis of vertebral osteochondrosis dissecans (OCD). The OCD was initially thought to be a cause for the ataxia, however histology and immunohistochemistry confirmed a diagnosis of multicentric diffuse large B cell lymphoma. Microscopic examination of the spinal epidural tissues in this case revealed extensive local infiltration by neoplastic B lymphocytes. In this case, both the epidural lymphoma and the vertebral OCD may have contributed to the horse’s neurologic presentation. However, the lack of histologic evidence of axonal Wallerian degeneration within the spinal cord at the time of death suggests that the neoplastic infiltrates are more likely to be the cause of the clinically noted ataxia than the vertebral OCD.
Neurologic signs including ataxia and paresis may be present if the central nervous system is affected, however lymphoma involving the brain, spinal cord and meninges causing ataxia is rarely reported (Morrison et al. 2008). Achieving an antemortem diagnosis of lymphoma is a significant challenge for veterinarians and horses are often diagnosed during post- mortem examination (Sheard and McGovern 2021). Spinal cord compression due to neoplasia in horses has been diagnosed ante mortem with myelography (Hirsch et al. 2009). Two cases of spinal lymphoma have been diagnosed ante mortem with one miniature horse surviving to 16 months with treatment until the time of the case report being written (Hirsch et al. 2009; Finding et al. 2014). In the present case there was no evidence of spinal cord compression and myelography would not have been helpful in achieving an ante mortem diagnosis of meningeal lymphoma. It has been suggested that lymphoma should be considered as a differential diagnosis in horses presenting with non-specific clinical signs or those horses who are unresponsive to treatment (Sheard and McGovern 2021).