On May 2, 2012, an alert was issued to the University of Liege in Belgium and to the RESPE that 23 clinical cases compatible with the diagnosis of atypical myopathy have been recorded so far this year. In France, there have been 18 cases, in Great-Britain 4 cases have been reported and 1 case has been reported in New Zealand.
Generalized weakness a symptom of atypical myopathy
Twenty-three clinical cases compatible with the diagnosis of atypical myopathy in horses have been recorded so far this year.
Horses with atypical myopathy suffer from severe, generalized weakness and are frequently found in lateral recumbency. Sometimes, they are found dead in the pasture without showing any earlier signs of the disease.
The emission of dark colored urine is probably the most specific clinical sign of atypical myopathy. If possible, collect a urine sample to show your vet to help him make a correct diagnosis.
Signs of colic can be present, most probably due to the difficulty to urinate. The distension of the bladder could indeed explain the signs of colic that usually disappear once the veterinarian empties the bladder. However, colic sign unresponsive to bladder emptying may indicate coexistence of abdominal colic and atypical myopathy.
Horses still able to walk exhibit stiffness, particularly visible at the hindquarter. It is important also to check other horses present on the same pasture for stiffness, because it can be an announcing sign of atypical myopathy.
In general, horses suffering from atypical myopathy are depressed. Often, they show difficulty or even inability to get on their feet and/or to stay standing. Muscular tremor and localized or generalized sudation can be observed. In spite of the severity of the clinical signs, often affected horses still want to eat (try to grasp any hay or grass that is near their mouth).
No clinical signs have been reported related to troubles of the central nervous system. Occasionally some paddling has been observed. This might be interpreted as a sign of suffering or/and anxiousness and/or desire to get up. It is important to mention that compared to the intense suffering of exertional myopathy, atypical myopathy seems less painful.