A case of post-anesthetic myopathy in a draft horse

Abstract

A 19-year-old Percheron mare was referred to the Cornell University Equine Hospital for colic of approximately eight-hour’s duration. Relevant history included a familial history of equine polysaccharide storage myopathy (EPSM). On presentation the patient was severely painful, tachycardic, and abdominal distention was appreciated. Surgical intervention was recommended based on clinical signs, a serosanguinous abdominocentesis, and marked lactic acidosis. Exploratory celiotomy revealed a large colon volvulus and mesojejunal rent, which were corrected without surgical complications. However, maintenance under general anesthesia during surgery was challenging, as the patient remained severely hypotensive and hypoxemic throughout the entire procedure. Upon post-operative recovery from general anesthesia, the patient was unable to stand. She was painful and anxious, and had severe muscle fasciculations, which were refractory to treatment with analgesics, anxiolytics and muscle relaxants. Her lactic acidosis had worsened significantly. Despite aggressive fluid therapy, she was oliguric and urinary catheterization produced a relatively small volume of red-brown urine. A presumptive diagnosis of post-anesthetic myopathy with a possible polysaccharide storage disease component was made based on the patient’s signalment, history, clinical signs, and complications under general anesthesia. The owners elected to euthanize based on her lack of response to treatment and poor prognosis. Discussion of the pathogenesis, predisposing factors, treatment and prevention of post-anesthetic myopathies in horses will follow case presentation.