Vertebral lymphosarcoma as the cause of hind limb paresis in a horse.

This research describes a case of lymphosarcoma, a type of cancer, in a horse that caused leg weakness leading to the inability to stand. The cancer was unique as it led to a mass developing within the vertebral bone, which has not been previously documented in horses.

Patient Presentation

• A 23-month-old female quarterhorse was brought to the Louisiana State University Veterinary Teaching Hospital for an inability to stand due to leg weakness.
• The owner had noticed abnormal head and neck posture 11 days prior and the horse became unable to stand 3 days prior to referral.
• On physical examination, the horse was found to be alert with normal reactions of the cranial nerves, reflexes and sensations of the forelimbs. The horse suffered from weakness of the rear legs, yet had intact patellar and withdrawal reflexes and sensory perception.

Initial Treatment and Findings

• A thoracolumbar spinal cord lesion was suspected and the horse was treated accordingly.
• After no improvement in 24 hours, the horse was euthanized.
• Autopsy findings revealed a mass within the vertebral canal of the lumbar spine. The mass was elongated, tan-white in appearance, and was compressing the spinal cord. A large round mass was also found in the spleen.

Microscopy and histological analysis

• A microscopic view of the vertebral, spleen, and lymph node nodules showed neoplastic round cells being the same in all tissues examined.
• The neoplastic cells had replaced the existing bone marrow and collected beneath the periosteum, leading to a protrusion into the vertebral canal.
• Within the spleen, multiple lobules of tissues composed of the same neoplastic cells were found.
• The nodules in mesenteric lymph nodes consisted of neoplastic cells that were identical to those in the vertebra and spleen.
• In certain lymph nodes, there were several large multinucleated giant cells in the medullary cords. These cells contained between 10 and 20 nuclei and abundant eosinophilic cytoplasm.

Discussion and Conclusion

• Lymphosarcoma in horses is generally rare and is usually diagnosed in middle-aged horses. This particular case was unique due to the uncommon involvement of vertebral bone.
• The cause of the horse’s symptoms was pressure on the spinal cord from the vertebral mass and associated degeneration in the cord.
• This case was multicentric in origin and the cell type was categorized as histiocytic.
• Despite the severe nature of the disease, there were no definitive clinical signs that could have allowed a diagnosis of lymphosarcoma in the horse before death.
• In conclusion, while vertebral involvement is rare in horses, instances of lymphosarcoma can result in severe spinal cord disease with significant clinical symptoms. Thus, uncommon manifestations of diseases, such as the vertebral involvement seen in this horse, should be considered when diagnosing animals presenting similar symptoms.