1. Why does intervertebral disk disease happen?
There are two general types of IVDD, Types I and II. Type I IVDD typically affects younger to middle aged chondrodysplastic dogs (smaller dogs with short legs) such as the Dachshund, and usually results in an acute onset of clinical signs. Type I IVD degeneration begins early in life in predisposed breeds. Over time, the center of the disk (called the nucleus pulposus) loses water content and undergoes calcification. As a result, the disk is prone to herniation and extrusion of disk material into the spinal canal causing compression of the spinal cord.
2. What are the signs to watch for?
Disc herniation results in varying degrees of pain and neurologic deficits depending on the site of disk herniation, degree of spinal cord compression, and amount of concussive injury or bruising to the spinal cord. Common signs may include reluctance to move or jump, holding the nose pointed to the ground (common in neck injuries), holding the head arched backwards (common in back injuries), screaming or crying when touched or picked up, trembling, an ataxic (wobbly or uncoordinated) gait, and dragging one or more legs (often both back legs).
3. Why aren’t x-rays sufficient to diagnose IVDD?
Radiographs (or X-rays) are an excellent diagnostic tool, and can be used to rule out other processes such as broken bones, cancer of the bone or infection of the bone. Radiographs can also suggest intervertebral disk disease, but do not provide enough information to allow for surgical planning. A myelogram can demonstrate cord compression, but is not specific for IVDD. This test is more invasive and involves injection of a contrast agent into the spinal canal. Computed tomography (CT) can also be used with or without a myelogram to identify the site of disk herniation. A CT does provide more detailed images of the bone and spinal cord than radiographs. However, Magnetic Resonance Imaging (MRI) provides the best imaging of the spinal cord and intervertebral disks. MRI allows detailed evaluation of the spinal cord and offers superior images for diagnosis and surgical planning.
4. I had a friend who’s dog recovered with steroids. Can’t we give my dog steroids?
Medical and surgical options are available for treatment of IVDD. Dogs that are more severely affected (pain that does not respond to medications and rest, and dogs that are showing neurologic signs such as wobbliness or dragging the back legs) are candidates for surgical management. Dogs that are less severely affected (first-time with pain only, or dogs that can still walk but are wobbly) may be treated with medical management. Medical management consists of strict cage confinement and medications to relieve pain. Anti-inflammatory drugs (ex. Rimadyl) or steroids (ex. Prednisone) can be used to reduce inflammation and pain associated with disk herniation, but should not be used in combination. Additionally, other pain medications may be used to keep pets comfortable. Typically, it takes dogs longer to recover if they are managed conservatively, their degree of recovery is less than with surgery, and the risk of recurrence is higher than with surgery.
“Mega-dose” steroids such as large amounts of dexamethasone or Solu-medrol (methylprednisolone sodium succinate) have fallen out of favor with most veterinary neurologists. There are several studies that support this. In one study, dogs treated with surgery alone had as high of a chance of recovery as those treated with surgery and steroids. In several other studies, dogs that received steroids had a higher likelihood of side effects such as stomach upset and urinary tract infections. Recently, a multi-institutional, placebo-controlled, double-blinded study comparing solu-medrol, polyethylene glycol and placebo was completed. While the results have not yet been published, the researchers have reported that there is no beneficial effect of solu-medrol OR polyethylene glycol over surgery alone.
5. What are the chances of fixing my dog?
Prognosis depends on the degree and duration of neurological signs and type of treatment. Many dogs treated conservatively can improve; however, time to recover is longer, completeness of recovery is less, and recurrence of clinical signs is higher. Many dogs with mild neurological signs (can walk, but are mildly incoordinated) can have a functional recovery with medical therapy. Dogs who are unable to walk, but can still move their legs, have a worse prognosis (50-60% chance) fore returning to normal function with medical management. The prognosis for paralyzed dogs treated conservatively is guarded with only 50% of dogs returning to an ambulatory status with fecal and urinary continence.
Dogs that are managed with surgery have a good prognosis for walking again even if they have severe neurologic deficits. Additionally, these dogs recover faster and have less chance of recurrence. Even paralyzed dogs have about a 95% chance of walking again with surgical treatment if they can still perceive pain in their affected limbs.
Prognosis declines if dogs lose the ability to perceive pain and is dependent on time. Dogs without pain perception have about a 50-60% chance of walking again with surgery if it is performed within the first 24 hours. However, the chance of walking is low (5%) if treated conservatively.
6. What are the chances of this happening again?
Recurrence of disk herniation occurs but is less common in dogs treated surgically. About 10-20% of dogs will herniate another disk at another point in their lifetime and may require surgery. Recurrence rates tend to be higher (40-50%) in dogs that are managed medically.