Movement disorders in dogs often indicate that something has compromised the spine's ability to perform its most important function: keeping the nervous system tissue it encloses safe from harm. When breakdown occurs in the communications that are constantly being sent and received by billions of neurons inside the brain and spinal cord, the body can lose the ability to coordinate muscle function in limbs. Several different diseases can present similar symptoms, including weakness leading to paralysis in the hind legs. If you notice any such signs in your dog, consult a veterinarian right away.
Hind Leg Weakness in Dogs
What the Spinal Cord Does
In vertebrates, the central nervous system consists of the brain and spinal cord. Enclosing and protecting the spinal cord is the spinal column, which we usually refer to simply as the spine. It consists of a series of bones -- vertebrae -- separated from each other by shock-absorbing cushions called intervertebral discs. Not only do these discs prevent the vertebrae from rubbing against each other, they're also flexible enough to act as joints, thereby allowing the spine to bend. In a healthy spine, communications between the central nervous system and the rest of the body proceed smoothly to coordinate movement and all other body functions. But if the spine is damaged, injuring the delicate tissue inside, these channels of communication can be disrupted or cut off, isolating parts of the body from the control of the central nervous system. The result can be partial or total limb paralysis.
Degenerative Myelopathy Destroys Spinal Tissue
Degenerative myelopathy, which typically strikes dogs between 8 and 14 years of age, causes progressive deterioration of spinal cord tissue, starting in the thoracic or chest region. Early signs include weakness and loss of coordination, first in one hind leg and then the other, causing the dog to drag his back feet, or "knuckle over," as he walks. An inherited gene mutation -- related to amyotrophic lateral sclerosis, or Lou Gehrig's disease, in humans -- makes some breeds, especially German shepherds, more vulnerable than others; Welsh corgis, boxers, Chesapeake Bay retrievers and Irish setters also have increased susceptibility. DM, which eventually leads to complete paralysis, can progress very rapidly but, according to Canine Genetic Diseases, dogs become paraplegic within six months to a year in most cases. Unfortunately, there's no treatment.
Ruptured Discs Can Cause Paralysis
If the outer covering of the discs between vertebrae break down, the nerves in the corresponding section of the spinal cord may be pinched or crushed, interfering with their ability to send and receive communications. "Slipped discs" can be caused by injury, but when the degeneration is due to chronic weakness, the condition is called intervertebral disk disease. Breeds with long backs and short legs, such as dachshunds and Basset hounds, are especially vulnerable. Other breeds believed to have a genetic predisposition include poodles, Pekingese, Lhasa apsos, German shepherds, Dobermans and cocker spaniels. The location of the ruptured discs determines which parts of the dog's body will be most affected. According to VCA Animal Hospitals, ruptured neck discks may cause weakness and paralysis in the hind legs first, leaving the front legs unaffected. Sometimes ruptured discs heal by themselves; but when paralysis is involved, vets may recommend surgery to relieve pressure on the spinal cord.
Wobbler Syndrome Affects Large Breeds
Wobbler syndrome, an intensely painful condition caused by compression of the spinal cord in the neck area, causes affected dogs to walk with a wobbly, unsteady gait, especially in their hind legs. In large and giant breeds such as Great Danes, Rottweilers, mastiffs, Weimaraners, German shepherds, Irish wolfhounds, Bernese and Swiss mountain dogs, this is usually caused by congenital malformation of neck vertebrae; in Dobermans, by ruptured neck discs. According to veterinarian Karen Becker, affected dogs often hold their heads low, dragging their rear legs as they walk. As the disease progresses, the front legs may also be affected, although usually not as severely. When treating wobbler's, the vet should make his top priority pain reduction and may use medications to reduce inflammation and swelling of the spinal cord. If these don't work, the only other option to improve quality of life is surgery, Becker says.