ULTRASONOGRAPHY OF THE EQUINE TRICEPS MUSCLE BEFORE AND AFTER GENERAL-ANESTHESIA AND IN POST-ANESTHETIC MYOPATHY

The ultrasonographic appearance of the equine triceps muscle of clinic ally normal horses, before and after general anaesthesia, was investig ated and compared with 5 cases of post anaesthetic myopathy, The trice ps muscle areas were examined bilaterally using a 7.5 MHz linear array probe in 2 different planes, with each limb both weightbearing and no nweightbearing, The triceps muscles of 4 unanaesthetised horses were s canned twice, 24 h apart. Six horses underwent general anaesthesis and were scanned pre-anaesthesia and at 1 and 24 h intervals after recove ry. Blood samples were obtained in the unanaesthetised group at each s can time and, in the anaesthetised group, pre-anaesthesia and at 10 mi n, 5 and 24 h after recovery. Creatine kinase (CK) and aspartate amino transferase (AST) concentrations were measured, Anaesthetic details an d recovery were related to the ultrasonographic and muscle enzyme find ings. Five horses with post anaesthetic myopathy were scanned at inter vals 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 h ad no change or a slight overall increase in echogenicity. The scans o f control unanaesthetised horses were unchanged on successive days, Al l anaesthetised horses had uncomplicated anaesthesis and recoveries an d did not exhibit any clinical signs of post anaesthetic myopathy, Ele vated CK and AST values were found up to 342 and 195%, respectively, o f the pre-anaesthetic values but no significant alterations in the ult rasonographic appearance of the muscles were detected, Clinical cases of post anaesthetic myopathy had disruption of the normal ultrasonogra phic pattern. There was an overall increase in echogenicity with a los s of the normal striated pattern, In 3 cases, there was localised incr eased echogenicity within the muscle, One of these horses was humanely destroyed for other reasons and histological examination of the affec ted muscle revealed a necrotic area correlating with the hyperechoic r egion, Two horses had bilateral involvement of the triceps musculature . Four horses recovered clinically from the myopathy and the ultrasono graphic appearance returned to normal except in 1 horse where focal hy perechoic regions remained 10 weeks after the onset of the clinical si gns.