Postanesthetic Equine Myopathy Suggestive of Malignant Hyperthermia: A Case Report

Abstract

Signs of malignant hyperthermia, including progressive increases in PaCO2, skin temperature and heart rate, and elevated serum levels of potassium, inorganic phosphate, and creatine kinase, were identified in a halothane-anesthetized horse. Treatment was discontinuing halothane administration, applying ice and cold fluids, and hyperventilating with 100% oxygen. After an initial recovery, bilateral hindlimb myopathy and pigmenturia developed. The myopathy resolved after treatment with oral dantrolene, IV fluids, and hydrocortisone. Results of caffeine-halothane challenge, using semimembranosus muscle collected 2 weeks after the episode, were considered within normal limits for horses. The intraoperative abnormalities were evidently predictive of postanesthetic myopathy but the cause in this horse remained unclear.

Association of a mutation in the ryanodine receptor 1 gene with equine malignant hyperthermia

“…RNA extraction and complementary deoxyribonucleic acid (cDNA) synthesis were performed according to manufacturer's instructions (RNeasy kit, Qiagen Inc., Valencia, California; and SuperScript II, Invitrogen, Carlsbad, California, respectively). Sixteen pairs of primers (forward and reverse, Table 1) were designed from consensus sequences for the human, pig, and rabbit (NCBI: NM_000540, M91451, X15209, respectively) to amplify RyR1 exons containing the mutations reported for the human (exons 2,6,9,11,12,14,15,17,39,40,44,45,46,96,101, and 102), 23,24,38 pig (exon 17), 8 and dog (exon 15). 33 The generated primers were designed to work with both genomic DNA (gDNA) and cDNA.…”

“…26 Since the onset of use of inhalation anesthesia in horses, cases of MH 16 have been suspected but seldom reported. The reported breeds are Quarter Horse, 5,21,32 Thoroughbred,17,21,43 Appaloosa, 21 Arab, 15 and ponies. 13,14 To date, the diagnosis of MH in horses is based on characteristic clinical manifestations triggered by halothane, 16,21,37,43 or abnormalities in the in vitro contracture test using halothane, succinylcholine, and caffeine.…”

Anesthetics, tranquillizers and opioid analgesics

“…Halothane has been reported to trigger a malignant hyperthermia-like reaction in horses infrequently, often in association with the use of the depolarizing neuromuscular blocking agent succinylcholine (suxamethonium) (Hildebrand & Howitt 1983,Hildebrand et a11990, Klein et al 1989, Manley et al 1983, Riedesel & Hildebrand 1985, Waldron-Mease et aI1981). Halothane has been reported to trigger a malignant hyperthermia-like reaction in horses infrequently, often in association with the use of the depolarizing neuromuscular blocking agent succinylcholine (suxamethonium) (Hildebrand & Howitt 1983,Hildebrand et a11990, Klein et al 1989, Manley et al 1983, Riedesel & Hildebrand 1985, Waldron-Mease et aI1981).…”

Pathological Findings of the Skeletal Muscles in a Racehorse Presenting with Malignant Hyperthermia-Like Symptoms after Halothane Anesthesia

“…The myopathy induced by metabolic abnormalities is involved with the use of anesthetics and muscle relaxants containing halothane and succinylcholine [2]. Several cases of myopathy induced by halothane anesthesia in equines have been reported in the United States [3,4,11]. Few studies, however, have described the details of the morphological changes in muscles, similar to those reported in humans [7,9,12].…”

“…It has been well-known that horses may develop astasia after anesthesia, and many such cases have been reported [3,5,11]. A typical equine-muscle disease causes astasia after anesthesia.…”