Narcolepsy is a rare and severe sleep disorder that has been reported in many mammals, writes Lee Benson in the March edition of The Horse
. In humans, it affects approximately one or two in 2,000; in horses, the incidence is probably even lower.
Studies of narcolepsy in humans revealed there are four components of the condition. The first is excessive daytime drowsiness, during which periods of rapid eye movement (REM) sleep might invade waking consciousness. The second is cataplexy, a sudden and temporary loss of muscle tone while conscious. Sleep paralysis is the third, and daytime hallucinations and/or extremely terrifying dreams are the fourth.
Excessive daytime drowsiness and cataplexy have been observed in horses. Because horses are unable to tell us whether they hallucinate, dream, or experience sleep paralysis, we don't know if the other two components play a part or not.
In narcoleptic horses, the sudden onset of REM sleep usually occurs during periods of inactivity--while the horse is in his stall, at pasture, or standing relaxed in a run-in shed. Typically, the horse will drop his head quite low and spread his front legs for balance while his hindquarters sag. The horse's eyes might be closed or half-open, and movement (REM) is visible. Most horses remain standing during attacks, but some, particularly ponies, sit on their haunches and might roll on their sides. Attacks can last from a few seconds to 10 minutes.
Cataplexy is a more problematic and potentially dangerous aspect of narcolepsy in horses because of the size of the animal. Simple actions such as stroking the head and neck, leading a horse out of his stall, hosing or bathing after exercise, or the intake of grain or water at feeding time can cause a narcoleptic horse to buckle suddenly at the knees, stumble, and possibly collapse. The best approach is to stand back and let the episode run its course. Within minutes, even seconds, the horse will regain control and return to normal.
Most literature on equine narcolepsy agrees that episodes associated with narcolepsy, particularly cataplexy, do not occur during exercise. However, reports from horse owners differ.
Imipramine, a tricyclic antidepressant, is used to treat narcoleptic horses with inconsistent results. Atropine sulfate relieves the condition in horses for up to 30 hours. Both drugs can cause colic attacks, so the risk far outweighs the benefit. Sharon Doolittle, a Rhode Island veterinarian, has treated narcoleptic horses successfully with the antidepressant amitriptyline.
With or without drug therapy, narcoleptic horses require a little more monitoring and attention to their environment than normal horses. If you suspect you've got a sleeper on your hands, consider these tips:
- Invest in breakaway snaps for your lead shanks and cross-ties.
- Install rubber padding on the walls and floor of the horse's stall.
- Remove any objects from the paddock, barn, and stall that could injure the horse if he were to collapse on or near them.