Femoral B-cell neurolymphomatosis in a horse with multicentric lymphoma

An 18-year-old Freiberger gelding was presented with a history of intermittent left hindlimb lameness after an acute onset 2 weeks prior to referral. The lameness had not responded to anti-inflammatory therapy prescribed by the referring veterinarian. Physical, orthopaedic and neurological examinations revealed signs compatible with ipsilateral femoral nerve dysfunction. Transrectal sonographic examination showed a marked increase in the diameter of the left femoral nerve. The results of electromyography of the left hind quadriceps muscle were compatible with denervation attributable to neuropathy. Evaluation of cerebral spinal fluid (CSF) revealed pleocytosis consisting of medium-sized lymphocytes, 5%-10% of which were positive for CD3 and CD79a. Neoplasia was suspected and steroid therapy was started. However, exacerbation of the clinical signs occurred and the horse was euthanised. Histopathological evaluation showed neurolymphomatosis of the left femoral nerve as the cause of the lameness. Infiltration of tumour cells was also seen to a lesser extent in the right femoral nerve, spinal cord, various parts of the cardiovascular system, renal capsules, an abdominal lymph node and the subcutis of the left stifle and upper lip. Histochemical evaluation revealed 60%-70% of the neoplastic lymphocytes were positive for CD20 and CD79a and up to 40% were positive for CD3. This report describes the uniqueness of a femoral mononeuropathy as the main clinical finding of B-cell neurolymphomatosis and multicentric lymphoma.