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Myotonia is a condition that results in constant contraction or delayed relaxation of voluntary muscles. It may be congenital, meaning that it is present before or at birth, or it can be an acquired condition later in life. A handful of dog breeds are known to be affected, and the condition is rare in cats. Pets with myotonia have a stiff gait and trouble getting up. They might have difficulty swallowing. Although there is no specific treatment for the disease, there is a drug that can reduce some signs in pets, but many pets with this condition are euthanized.
The congenital form of this disease, more aptly termed myotonia congenita, is caused by a defect in the muscle membrane. Chloride channels within the membrane (which allow complex electrical impulses to pass from nerves to muscles) do not function properly, resulting in constant contraction or delayed relaxation of voluntary muscles (like that of most of the skeletal system).
In some cases, myotonia has been found to be acquired; that is, dogs with certain conditions may also experience chloride channel disturbances by virtue of their primary disease. Cushing’s disease has been associated with myotonia in dogs, and some infectious or immune-mediated conditions may also result in similar signs.
Dogs with myotonia exhibit a stiff gait, have trouble rising, and may have an abnormal bark and difficulty swallowing. Young dogs start to show signs as early as a few weeks old, although the acquired form may occur at any age.
A DNA test pioneered by the University of Pennsylvania is currently available to screen for both carriers and diseased Miniature Schnauzers. Muscle biopsy and electromyography (or EMG, a study of electrical impulses in the muscles) have also been shown to be helpful in diagnosing the problem.
Chow Chows and Miniature Schnauzers have been documented as affected breeds.
Procainamide, a drug usually used to treat heart arrhythmias, has been found to reduce the signs in many affected dogs. Apart from this approach, nothing is known to be effective, including (to date) treatment of the underlying disease in those who have acquired (noncongenital) forms of myotonia. Few dogs will ever be free of symptoms altogether and many are euthanized.
Prevention of congenital myotonia is achieved primarily through testing of affected breeds and removing carriers or affected patients from the breeding pool through spay and neuter. A campaign is currently underway by the University of Pennsylvania to test all Miniature Schnauzers intended for breeding to completely eliminate the problem in this breed.
This article has been reviewed by a Veterinarian.
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