ELECTROMYOGRAPHY IN ACQUIRED EQUINE MOTOR-NEURON DISEASE

A systematic study of the electromyographic (EMG) changes in horses wi th histopathologically confirmed equine motor neuron disease (EMND) wa s performed in 20 horses. Needle EMG of a select group of distal and p roximal thoracic and pelvic limb and epaxial muscles were recorded fro m horses under general anesthesia. Quarter Horses (10; 50%) were the m ost common horse in this study. Clinical signs of weight loss, muscle atrophy and generalized weakness were present in all horses at the tim e of the study. Muscle fasciculations occurred in 12 (60%) horses. The presence of muscle fasciculations and elevated serum creatine kinase activity was significantly dependent on the duration of clinical signs , with both seen more frequently in horses with clinical signs for les s than 6 months. Prolonged insertional activity was present in all hor ses. Distal limb spontaneous activity (SA; presence of electrical acti vity recorded from muscles without voluntary contraction) was independ ent of limb being tested. Proximal limb SA, however, was significantly dependent on limb location. All horses were identified to have SA in the proximal thoracic limb compared to only 11 (55%) of horses with SA in the proximal pelvic limb. An almost equal distribution of epaxial muscle SA was found in the cervical region compared to the remaining e paxial musculature. Positive sharp waves were the most common waveform of SA recorded. No consistent pattern of muscle histologic changes wa s associated with EMG abnormalities. Overall, this study demonstrated that horses with EMND have a high prevalence of EMG changes (100% of c ases studied), with multiple areas affected (two or more), and a predi lection for the proximal thoracic appendicular muscles to be involved. The results of this study indicate that the antemortem diagnosis of E MND can be enhanced with needle EMG studies of horses under general an esthesia.