Spinal Muscular Atrophy (Motor Neuron Disease) in Dogs

The degeneration or death of the motor neurons in the spinal cord and brainstem causes the impulse not to be able to transmit to the muscles.  Therefore, the muscles do not contract, nor move.

Motor neuron disorders are also called hereditary canine spinal muscular atrophy (HCSMA).These disorders are autosomal dominant. The severity and progression of the disease can be different depending on the dog’s breed. Dogs diagnosed with HCSMA should not be bred.

Spinal muscular atrophy (motor neuron disease) causes degeneration and/or death of the motor neurons (motoneurons) in the spinal cord.  A motor neuron is a nerve cell, which is located in the spinal cord.  The axon of the motor neuron extends from the spinal cord and “transmits” impulses to the muscles. These impulses cause the contraction of the muscles, which results in the ability to move.

The severity and progression of the clinical signs will vary between dogs of different breeds.  

• Reduced reflexes
• Abnormal gait
• Loss of muscle mass
• Weakness of hind or front legs
• Poor coordination
• Lack of appetite
• Head tremors
• Difficulties swallowing
• Inability to swallow
• Increased weakness
• Diminished growth
• Inability to hold head up
• Unable to move
• High body temperature 

Types

Spinal muscular atrophy (motor neuron disease) conditions which affect different types of breeds are:

• Spinal muscular atrophy - Brittany Spaniels
• Focal spinal muscular atrophy - German Shepherds
• Motor neuron disease - Rottweilers
• Multisystem chromatolytic neuronal degeneration - Cairn Terrier

Motor neuron diseases are autosomal dominant, which are passed down by inheritance.  Autosomal dominant disorders only need one mutated gene from either the dam or sire for the disorder to be passed on to the litter. 

• The motor neurons degenerate
• Impulses are not transmitted to the muscles
• Movement cannot take place

The veterinarian will want to go over the patient’s medical history.  He will want to know what symptoms you have observed and when they started.  The veterinarian may want to evaluate the gait during walking.  He will then perform a neurological examination, which may include pupillary light reflex, palpate muscles for atrophy, check spinal, pelvic and thoracic limb reflexes. The veterinarian may want to schedule your dog for a muscle biopsy procedure. A small piece of muscle tissue is cut out and sent to a laboratory for testing.

General anesthesia is usually administered for this procedure. The veterinarian may also recommend x-rays of the limbs and an electromyogram. Electromyography (EMG) records electrical activity within the muscles; a small needle electrode is inserted into the muscle. The patient will need to have general anesthesia for this procedure as well. A nerve conduction test may also be suggested.

There is no known treatment or cure for spinal muscular atrophy/motor neuron diseases in dogs.  Most anti-inflammatory medications are unresponsive to the disorders.  There have been improved clinical symptoms using fampridine. Fampridine (4-aminopyridine) increases the release of neurotransmitters.  It can restore conduction to demyelinated axons and improve neurological activity.  

Patients with chronic spinal muscular atrophy may be thin but can live full lives.  The symptoms may be very mild and progress slowly. The veterinarian may also recommend manual physical therapy and acupuncture.  Aquatic therapy may also be helpful. Aquatic therapy may include underwater treadmills and swimming. Being in the water will take pressure off your dog's limbs and may improve muscle tone. The veterinarian may recommend neuromuscular electrical stimulation (NMES).  

NMES gives off low volt electrical stimulation to the motor nerves to cause muscle contractions. Dogs that are not able to use their hind legs may find a lifting dog harness or wheelchair helpful. If the patient is overweight he may be placed on a low calorie diet to help him lose weight.  Nutritional supplements and vitamins may be added to his diet, such as omega-fatty acids, vitamin E, vitamin C, and B-complex.

Dogs and puppies severely affected by motor neuron disease may need to be humanely euthanized. Patients with slow progressive spinal muscular atrophy (motor neuron disease) will need to be monitored for their condition. They can live happy lives with a few modifications. The patient will benefit from attending regular manual and/or aquatic therapy.  If your dog is taking fampridine (4-aminopyridine) he will need to be monitored for any side effect caused by the medication. Side effects may include seizures and atrial fibrillation.