Narcolepsy is a rare sleep disorder that has been recognised in many species. The condition affects around 1 in every 2000 humans, however the true incidence of narcolepsy in horses is unknown.
Narcolepsy in horses, and many other mammals, is characterised by periodic episodes of “cataplexy”. Muscle function is temporarily affected resulting in mild weakness to complete collapse. During most attacks horses will regain strength and stand without falling, but occasionally horses may fall completely.
Horses suffering from narcolepsy may show unexplained abrasions or injuries associated with weakness or collapse, especially over the fetlocks and hocks.
In humans, emotions can be triggers for narcoleptic attacks. However, in horses, attacks can occur during routine activities such as leading a horse out of their stable, hosing off after exercise, or during the first mouthful of water or feed. There is even the potential for a horse to suffer a narcoleptic attack during riding.
The exact cause of narcolepsy is not known. Diagnosis can be challenging as episodes can be difficult to observe, although video recording of a horse in his stall can be helpful. It is very important to rule out other conditions that may cause sudden collapse, such as heart conditions, seizures and other neurological diseases.
Unfortunately, there is no cure for narcolepsy in horses or humans. One of the more common drugs used in human patients, imipramine, has been used in horses with inconsistent results. The negative side effects of such medications should also be considered.
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