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Horse - Thoroughbred 7-year-old Thoroughbred mare
Lame in left thoracic limb
This mare was pastured with other horses. She was normal the day prior to presentation. That morning, she was found walking with an abnormal gait. No trauma had been observed. The referring veterinarian diagnosed a generalized ataxia and treated her with 0.1 mg/kg IV dexamethasone, 1gm/kg IV DMSO and 1.1mg/kg IV banamine. She was referred 12 hours later
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Left suprascapular nerve
The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. These muscles act to help support the shoulder joint. The loss of their function results in a lateral buckling of the shoulder joint on weight bearing causing it to "pop out". The infraspinatus muscle normally inhibits medial rotation of this joint on weight bearing. The loss of this function results in excessive medial rotation of the humerus which is observed as a lateral movement of the olecranon at the elbow. This nerve has no cutaneous somatic afferent branches for clinical testing. By 10 to 14 days after denervation, these muscles will atrophy which is referred to as "Sweeney".
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Left suprascapular nerve injury
A common site for injury of the suprascapular nerve is where it crosses the scapular notch on the cranial surface of the neck of the scapula to innervate the supraspinatus and infraspinatus muscles. Many horses with this suprascapular nerve injury will exhibit a spontaneous improvement of their gait in a few weeks. The atrophy often persists. Chronic cases may be improved by surgical removal of the fascial band associated with the supraspinatus muscle that crosses over this nerve at the level of the scapular notch.
A standing EMG was performed under xyalzine. There was increased insertional activity and abnormal spontaneous activity (fibrillation potentials) in the supraspinatus and infraspinatus muscles in the left thoracic limb. No abnormal spontaneous activity was observed in the triceps brachii, biceps brachii and antebrachial muscles of the left thoracic limb nor any muscles of the right thoracic limb.
No treatment was recommended and significant spontaneous improvement was observed by 3 weeks after the onset of the lameness.
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