Forelimb tic in a horse.
An 18-month-old male Quarter Horse was referred for evaluation of a tic that had started after injury to the right forelimb 4 weeks earlier. The right forelimb appeared paretic and had constant regular twitches of variable intensity that were usually sufficiently forceful to move the trunk, neck, and head. The horse frequently threw the limb forward. The twitch persisted during sleep but disappeared during general anesthesia and following sedation with xylazine. It was unaffected by acetylpromazine, diphenylhydantoin, diazepam, carbamazepine, trimethadione, procainamide, quinidine, propranolol, dantrolene, methocarbamol, dimethyl sulfoxide mixed with xylocaine, or by low volar nerve anesthesia. It remained unchanged during 21 days of hospitalization but had stopped 10 weeks after discharge. Electromyographic tracings of the limb and neck and radiographs of the cervical and proximal thoracic spine, scapulohumeral joints, and adjacent ribs were normal. A localized spinal cord lesion or peripheral neuropathy and neuralgia secondary to trauma were suspected.
D000818:Animals; D005552:Forelimb; D006734:Horse Diseases / Q000175:diagnosis*; D006736:Horses; D006801:Humans; D013981:Tic Disorders / Q000662:veterinary*