The research article investigates an unusual case of a 21-year-old Quarter Horse that suffered from a type of lameness in its left pelvic limb due to B cell lymphoma. The study underscores that despite its rarity, disseminated lymphoma with direct nerve infiltration should be considered as a diagnosis in horses with peripheral neuropathies.

Investigation and Diagnosis

• When the Quarter Horse was presented, it had been suffering from chronic lameness in the left pelvic limb, which had been worsening over 3 weeks. An initial examination saw a visible lameness at a walk and neurological examination indicated sensory and gait abnormalities, suggesting a problem with the left femoral nerve.
• The horse was unable to fully advance the leg forward and exhibited a shortened stride length. Also, it put less weight on the limb due to the heels of the left hind foot not making full contact with the ground during the stance phase.
• Subsequent diagnostic imaging tests, including ultrasound and nuclear scintigraphy, were unable to pinpoint the cause of the problem. However, a blood test identified severe lymphocytosis (an exceedingly high number of lymphocytes), suggesting a lymphoma issue.

Postmortem Examination and Findings

• Following the horse’s death, a postmortem examination discovered swelling of the left femoral nerve and revealed that multiple masses were present in several locations, such as the stomach, large colon, adrenal gland, mesentery, heart, and meninges.
• A thorough dissection of the entire left pelvic limb struggled to reveal other causes of the gait problems. However, when studying the swollen femoral nerve, the histologic evaluation discovered that B cell lymphoma cells were present. These lymphocytes were differentiated in a way that suggested they had become plasma cells.
• The researchers found that these lymphocytes had infiltrated the femoral nerve at the swelling point and other peripheral nerves. This case, therefore, represents a rare neurolymphomatosis instance, where the femoral nerve paresis is directly caused by neoplastic lymphocyte infiltration resulting from disseminated B cell lymphoma.

Conclusion

• Although it is not a usual cause, the study recommends considering disseminated lymphoma with direct nerve infiltration as a potential diagnosis in horses showing symptoms of peripheral neuropathies. The understanding and awareness of such cases can aid in better diagnosis and treatment of similar future occurrences.