title: Ultrasonography of the equine triceps muscle before and after general anaesthesia and in post anaesthetic myopathy.
abstract: The ultrasonographic appearance of the equine triceps muscle of clinically normal horses, before and after general anaesthesia, was investigated and compared with 5 cases of post anaesthetic myopathy. The triceps muscle areas were examined bilaterally using a 7.5 MHz linear array probe in 2 different planes, with each limb both weightbearing and nonweightbearing. The triceps muscles of 4 unanaesthetised horses were scanned twice, 24 h apart. Six horses underwent general anaesthesia and were scanned pre-anaesthesia and at 1 and 24 h intervals after recovery. Blood samples were obtained in the unanaesthetised group at each scan time and, in the anaesthetised group, pre-anaesthesia and at 10 min, 5 and 24 h after recovery. Creatine kinase (CK) and aspartate aminotransferase (AST) concentrations were measured. Anaesthetic details and recovery were related to the ultrasonographic and muscle enzyme findings. Five horses with post anaesthetic myopathy were scanned at intervals after the onset of clinical signs. In normal horses, the triceps muscle appeared ultrasonographically as echoic striations separated by anechoic areas. The fascia dividing muscle bellies was visible as an echoic line. Ultrasonographs obtained with the limb nonweightbearing had no change or a slight overall increase in echogenicity. The scans of control unanaesthetised horses were unchanged on successive days. All anaesthetised horses had uncomplicated anaesthesia and recoveries and did not exhibit any clinical signs of post anaesthetic myopathy. Elevated CK and AST values were found up to 342 and 195%, respectively, of the pre-anaesthetic values but no significant alterations in the ultrasonographic appearance of the muscles were detected. Clinical cases of post anaesthetic myopathy had disruption of the normal ultrasonographic pattern. There was an overall increase in echogenicity with a loss of the normal striated pattern. In 3 cases, there was localised increased echogenicity within the muscle. One of these horses was humanely destroyed for other reasons and histological examination of the affected muscle revealed a necrotic area correlating with the hyperechoic region. Two horses had bilateral involvement of the triceps musculature. Four horses recovered clinically from the myopathy and the ultrasonographic appearance returned to normal except in 1 horse where focal hyperechoic regions remained 10 weeks after the onset of the clinical signs.
authors.affiliation: Department of Farm Animal, Royal Veterinary College, Hatfield, UK.
authors.forename: R K
authors.initials: RK
authors.lastname: Smith
authors.forename: S J
authors.initials: SJ
authors.lastname: Dyson
authors.forename: M J
authors.initials: MJ
authors.lastname: Head
authors.forename: R J
authors.initials: RJ
authors.lastname: Butson
mesh_terms: D000762:Anesthesia Recovery Period; D000768:Anesthesia, General / Q000662:veterinary*; D018681:Anesthetics, General / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001219:Aspartate Aminotransferases / Q000032:analysis / Q000097:blood; D001835:Body Weight / Q000502:physiology; D003402:Creatine Kinase / Q000032:analysis / Q000097:blood; D005260:Female; D006736:Horses / Q000033:anatomy & histology* / Q000378:metabolism / Q000502:physiology; D007275:Injections, Intravenous; D007649:Ketamine / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000201:enzymology / Q000473:pathology*; D013874:Thiopental / Q000008:administration & dosage / Q000494:pharmacology; D014463:Ultrasonography
chemical_list: D018681:Anesthetics, General; D007649:Ketamine; D001219:Aspartate Aminotransferases; D003402:Creatine Kinase; D013874:Thiopental