Myelin is the fatty protective sheath that covers every nerve in the body. This includes the nerves in the central nervous system and the nerves in the brain. When this protective covering becomes too thin the electrical impulses are lost between nerves; this is called hypomyelination. There are a few disorders that can cause this sheath to either decline or to not develop properly initially. The disorders relating to hypomyelination are genetic in nature and although the conditions can be managed, there is no cure at this time.

Hypomyelination is a disorder that causes a disruption in the electrical impulses between nerves due to a deficiency in the myelin sheath covering the nerves.

In early onset disorders:  

In adult onset disorders:

The causes of hypomyelination disorders are most often genetic in nature. Certain breeds are more likely to develop specific varieties of hypomyelination. 

Hypomyelinating Neuropathy 

Your veterinarian will want a full history for your pet, including when the symptoms began and under what circumstances. Your dog or puppy will undergo a thorough physical exam, and tests will be run to analyze blood chemistry and check for imbalances or toxins in the system. The physical exam may also include a neurologic examination to determine if any portions of the spinal cord are damaged, and where any damage is located. X-rays of the chest and back area will be examined to screen for tumors along the spinal cord or other evidence of cancers, and a sample of the patient’s cerebrospinal fluid may also be analyzed. Tests may be run to detect the genetic mutation responsible for the disorders, although some dogs may carry the mutation without ever developing the actual condition.

Procedures that may be used to rule out other disorders:

Diagnosis is considered a diagnosis of exclusion as the only definitive way to diagnose these disorders is to microscopically examine the spinal cord of the animal during necropsy. The technique used to make this diagnosis is called histopathology.

With the early onset disorder of hypomyelinating neuropathy there is no treatment. Many of the affected pups will outgrow at least the most obvious of symptoms, although there is a good chance that they will retain minor hind leg trembles throughout their lives. Some breeds will have a better prognosis than others. The form of genetic transfer is different in the Springer Spaniel breed. Females as well as males may be affected, although the male pups have much more pronounced symptoms. While the tremors that are present in female Springer Spaniel pups generally fade out by the time they reach four to six weeks old, it is almost always fatal for the male pups within the first six months. 

There is no cure for adult onset disorders either, but there are supportive measures that can be taken to improve your pet’s quality of life. Exercise and physical therapy are encouraged in many cases to delay the wasting of the muscles as well as to maintain flexibility and strength in the pelvic area. Water-based therapy techniques such as underwater treadmills and swimming may provide additional postponement of muscle deterioration. Manual “range of motion” exercises are notably beneficial.

Puppies that are affected by hypomyelinating neuropathy may require hand-feeding as the shaking makes it difficult to compete with siblings for food. Using the dam of an affected puppy for subsequent breeding is not suggested, nor is it recommended that the sisters be allowed to produce any litters. This is particularly important in the Springer Spaniel breed due to the disorder’s lethality. 

Dogs that develop hypomyelination disorders later in life benefit greatly from careful supportive care. Exercise is endorsed, including “range of motion” exercises and water-based physical therapy. Mobility devices such as special harnesses and wheel-carts can also be used to help keep your dog active longer. Well-padded bedding and soft, comfortable things should be available for your pet to rest on. These disorders can cause some incontinence in dogs as well, so removable covers and washable bedding are vital. As dogs may find have difficulty turning over in bed owners may need to turn them to avoid bedsores or lung collapse.