Equine ATYPICAL MYOPATHY, also called ATYPICAL MYOGLOBINURIA, is a frequently fatal condition affecting grazing horses in autumn and/or spring. The clinical signs of this myopathy seem to appear after typical climatic conditions. The condition has been recognised for the first time in 1984 and since several clinical cases have been described in different countries in Europe. Belgium was confronted with the disease for the first time during the year 2000. In France the first cases have been described in the autumn of 2002.
Up to recently, the scientific literature about the clinical signs, diagnostic tools and epidemiology of this condition was sparse. Seen the acute appearance of atypical myopathy in previously not-affected countries, the scientific community was rarely prepared to manage ten and sometimes even a hundred cases of atypical myopathy in a couple of days. Thus, the first part of the research performed at the Veterinary Faculty of Liege consisted of collecting available information about Belgium cases and to resume this in order to communicate it to owners and equine practitioners (see “literature”). Now, epidemiological studies have enlarged to all European cases owing to the collaboration many Veterinary Faculties and members of the AMAG.
Thanks to the collected information, the knowledge concerning clinical signs, diagnostic tools and preventive measures has improved enormously. Unfortunately, no curative treatment is available at this time, but supportive therapy, partially based on the recently identified pathological process in muscular mitochondria from affected horses, may be recommended.
The cause (aetiology) of atypical myopathy remains unknown. Nevertheless, it remains possible to prevent her apparition by using prevention techniques .
Treatment:In face of a horse suspected to suffer from atypical myopathy, a symptomatic treatment can be installed. This will not fight the causal agent (since it is not recognized yet), but will fight and decrease the symptoms. The objectives of this treatment consist of limiting the suffering of the horse, give a stop to muscular destruction, correcting electrolytic imbalances, reassuring the hydration status of the horse, supporting renal function and preventing complications. In addition to this supportive treatment that may be recommended for any rhabdomyolysis (i.e. muscle destruction), a specific treatment for atypical myopathy may be recommended based on samples such as blood, muscle or urine
Facing a case of atypical myopathy, somes measures has to be taken by the veterinarian. The owner has also a great role to play to help its horse affected by atypical myopathy (see the heading: “Alert: facing a case of atypical myopathy, measures to be taken by the horse’s owner).
Prognosis: According to the literature prior to the autumn 2006, atypical myopathy has a mortality rate above 85%. However, the last clinical series have been less devastating with a lower mortality rate (around 70%). This rate differs significantly among countries and clinical series. In France, this rate dropped to 40% during the autumn 2006 (vs. 70% in other countries).
Preliminary analysis of these European cases indicates that administrating a medical treatment (see “Alert: facing a case, the veterinarian”) increases the chance to survive. Nevertheless, in regard to the high fatality rate, any treatment should be attempted only when the horse’s suffering appears limited. Prognostic factors for survival are: normal mucosae, no sign of respiratory distress and remaining standing most of the time. It is worth noting that survivors had an uneventful recovery and surprisingly only showed minimal muscle wastage.