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Understanding LS disease

Q: I recently brought my dog Alice to the vet because she was limping on one of her back legs. She got diagnosed with LS disease. Can you please help me understand what this disease is and what my treatment options are?

A: Lumbosacral disease, or LS disease, refers to a disease of the lower back. Let me start by explaining the anatomy of the lumbar spine, as that will help you better understand what is happening with your dog.

The vertebrae are the bones that surround and protect the spinal cord. Dogs and cats have 7 cervical (neck) vertebrae, 13 thoracic (chest) vertebrae, 7 lumbar (lower back) vertebrae, a sacrum (tail bone) and then a varying number of vertebrae that make up their tail. (Humans differ from dogs and cats in that they only have 12 thoracic vertebrae, 5 lumbar vertebrae, and only a small number of “tail vertebrae” called the coccyx).

Each vertebra is named by the segment of spine it is in. For example, the cervical vertebrae are named C1 through C7, the thoracic vertebrae are named T1 through T13 and the lumbar vertebrae are named L1 through L7.

The spinal cord extends from the brain and passes through a canal in the vertebrae. The spinal cord does not extend all the way to the tailbone, however. In humans, the spinal cord stops at the end of the chest (at about T12). In dogs, the spinal cord extends into the lumbar vertebrae and ends around L6, but it varies from dog to dog.

This is an important anatomical fact. Once the spinal cord ends, the structure beyond that is called the “cauda equina” (which means “horse’s tail” in Latin). The cauda equina is not one thick spinal cord, but rather it is composed of many small nerves that run through the rest of the spinal canal.

This end of the spinal cord is appropriately named because when the spinal cord diverges out it looks like a horse’s tail. For people, the fact that the lumbar vertebrae do not have a large spinal cord running through them is protective against severe injuries such as paralysis, because there is more “play” in the spinal canal.

In dogs, the space between the last lumbar vertebra (L7) and the tailbone (sacrum) is called the LS space, and in most dogs the cauda equina is running through the vertebral canal in this area.

The sacrum is the part of the body that the pelvis connects up to. The pelvis moves the sacrum and this creates a lot of movement in the LS area. The LS area experiences the most movement of all of the lumbar vertebrae, which makes it a common area to get injured.

All sorts of problems can occur at this joint space. For example: the disk in between the joints can herniate up into the cauda equina; arthritis can occur around the vertebrae and tail bone irritating the nerves that come off the cauda equine; or the ligaments that hold the vertebrae and tail bone in alignment can overgrow and scar from repetitive injury, which can narrow the space through which the cauda equina passes through.

All of these diseases processes can “pinch” the nerves causing pain and injury to the nerves. The nerves that pass through this area help move the back legs and also help with urinating and defecating. When those nerves are damaged, sometimes symptoms such as dragging of the feet, difficulty urinating and defecating or, rarely, paralysis of the back legs can occur.

Pain from LS disease is common, but it is often confused with other diseases. This disease can mimic symptoms of hip or even knee arthritis, so careful examination of the patient is necessary to determine the true cause of the lameness. X-rays are also very useful to look at the bony structures in this area.

When evaluating a patient with LS disease and lameness, it is important to ascertain if the lameness is from pain alone or if there is also compromise of nerve function. Pain alone can make a patient not want to use a limb and lead to lameness. However, if the injury to this joint is severe, sometimes the nerve function is impaired so much that the limbs literally cannot move properly.

Your veterinarian can determine this by checking the patient’s reflexes. One simple reflex test is called the Conscious Proprioceptive (CP) Reflex. To test this reflex, you flip the foot under so the patient is standing on their “knuckles.” A normal patient will flip the foot back right away.

In a patient with a nerve deficit, they won’t be able to feel that their foot is out of place or won’t be able to respond quickly to replace the foot.

For patients with pain alone, medical management is started. Anti-inflammatories (like Rimadyl) and often gabapentin (used most commonly for nerve pain) are prescribed. Acupuncture can also be helpful in aiding in pain relief.

After an acute injury, it is important to rest the patient by not allowing them to jump or run. Slow, short walks are still acceptable. For patients that respond to medical management, a slow reintroduction to normal activity can occur typically in 4–6 weeks.

However, it is important to note that sometimes repetitive injury to the LS area is what weakened this part of the back to begin with. The most common movement that can cause repetitive injury is jumping, particularly in dogs that jump to catch a Frisbee or jump as part of rough play.

It is important to examine the lifestyle of your dog and determine if you can alter the type of play you do with them to help prevent further injury. For example, if your dog loves to jump for the ball, try throwing the ball in a way so that they don’t jump for it but rather pick the ball up off the ground to retrieve it.

For patients whose pain is not well controlled or who have associated nerve deficits, more aggressive therapy is indicated. Your veterinarian can refer you to a veterinary neurologist for a further work-up. The neurologist will likely want to perform an MRI to better assess the degree of injury to that area. Once that information is ascertained, treatment options, including steroid injections around the nerves and sometimes surgery to decompress this area of the spinal canal, can be performed.

Not all clients want to see a neurologist with their dog. Cost concerns, the pet’s age and individual philosophy about pet health care all factor into the decision-making process.

For pets that are weak from LS disease, managing their pain medically is important, as this can sometimes improve their weakness. Other mobility aids can also be beneficial.

I recommend Power Paws (traction socks) and Dr. Buzby’s ToeGrips (rubber nail covers) for pets that are slipping from weakness or have a hard time getting up, especially on hardwood or tile.

I also recommend the chest and pelvis harness system called Help ’Em Up. This durable harness set has handles on it so you can help your pet during times when she has hard time walking, like stairs, getting into the car or getting up from laying down.

Dr. Teresa Hershey is a veterinarian at Westgate Pet Clinic in Linden Hills. Email her your pet questions at drhershey@westgatepetclinicmn.com.