The effectiveness of spinal accessory nerve branch biopsy evaluation as a means to confirm the diagnosis of equine motor neuron disease (EMND) was investigated. Sixteen horses with histories and clinical signs suggestive of EMND and 16 control horses with neither histories nor clinical signs of any neurological disorder, were subjects of the study. Biopsy samples of the ventral branch of the spinal accessory nerve were obtained either surgically, under general anaesthesia or post mortem immediately after euthanasia. Evaluation was done on the spinal cord of all horses to serve as the definitive diagnostic indicator of EMND.
Results indicate that biopsy of the ventral branch of the spinal accessory nerve is a reliable ante mortem diagnostic test for EMND. Histological evidence of the degeneration of myelinated axons is present in both acute and arrested cases. The ventral branch of the spinal accessory nerve is easy to approach surgically and biopsy of the nerve causes no disfigurement of the sternocephalicus muscle. The use of semi-thin Epon sections is an excellent method of sample preparation. Formalin fixation and routine paraffin embedment may prove more accessible and provide good quality preparations for reliable interpretation. In the hands of an experienced pathologist, the sensitivity and specificity reliability coefficients for spinal accessory nerve branch biopsy are 94%, making this technique an extremely valuable diagnostic tool for the ante mortem diagnosis of EMND.