What is discospondylitis?
Discospondylitis is a bacterial or fungal infection of the intervertebral disks and the adjacent vertebral bones. Intervertebral disks lie between vertebrae in the vertebral column (spine or backbone). Discospondylitis may occur at one particular location within the spinal column, or it may occur at multiple sites.
Discospondylitis is primarily a disease of dogs. It is very rare in cats; only a few reported cases have occurred.
What causes discospondylitis?
Discospondylitis occurs when bacteria or fungi reach the intervertebral disks.
There are several ways that this can happen:
- Hematogenous (blood-borne) spread. In this situation, bacteria or fungi enter the bloodstream through a wound or infection. Blood flows through the intervertebral disk space and this can allow the bacteria or fungi to be deposited in this area, leading to infection. This is the most common source of discospondylitis.
- Direct contamination. This can occur when bacteria or fungi are deposited directly adjacent to the disk. This is typically associated with a deep bite or puncture wound directly over the spinal column, although direct contamination may also result from surgical procedures involving the spine.
- Migrating foreign body. In this situation, foreign material (such as a grass awn) within the body may migrate towards the spinal cord. These foreign bodies may enter the body through inhalation, ingestion, or a penetrating wound. If they contain bacterial or fungal contamination, discospondylitis may result.
Some dogs are more likely to get discospondylitis than others. Chronic infections (such as chronic skin disease) and immunosuppression (due to steroids, chemotherapy, or other underlying conditions) may predispose a dog to discospondylitis. Discospondylitis is most common in large-breed dogs, with Great Danes, German Shepherds, Boxers, Rottweilers, Doberman Pinschers, and English Bulldogs appearing to be at higher risk than other breeds.
What are the clinical signs of discospondylitis?
The signs of discospondylitis often begin gradually and slowly progress over time. In many cases, the first sign of discospondylitis is back pain. Your dog may act stiff, reluctant to jump on or off furniture, or may act painful when he turns a certain way or is touched in a certain location. As the condition progresses, additional signs may include stiffness and muscle weakness in the limbs. In severe cases, a dog may become paralyzed.
Many affected dogs, though not all, also show nonspecific signs such as decreased appetite, weight loss, and lethargy.
How is discospondylitis diagnosed?
Discospondylitis is often diagnosed using spinal X-rays. Although the disk itself cannot be seen on X-rays, discospondylitis causes changes in the bony vertebrae adjacent to the affected disk. These changes become visible on X-rays two to six weeks after the initial onset of clinical signs. Because of this delay, your veterinarian may need to repeat X-rays multiple times if your pet has back pain that does not respond to symptomatic treatment.
"Discospondylitis is often diagnosed using spinal X-rays."
In some cases, advanced imaging may be required. These tests include myelography (imaging involving dyes), CT scan, MRI, or bone scintigraphy (imaging involving radioactive tracers). Although these tests are expensive, typically requiring referral to a specialist, they are far more sensitive for discospondylitis than X-rays.
If testing suggests discospondylitis, your veterinarian may perform additional tests in an effort to confirm the type of infection. This allows your veterinarian to prescribe the most appropriate treatment. These tests may include blood cultures, urine cultures, and testing for an infection called brucellosis (a common source of discospondylitis).
Additionally, your veterinarian may recommend a cerebrospinal fluid (CSF) tap. A CSF tap involves collecting a small amount of CSF fluid (the fluid that bathes the brain and spinal cord) from an anesthetized patient, using a special needle. This fluid is examined for abnormal cells, protein levels, and other laboratory parameters.
In some situations, a neurologist may attempt to obtain a culture directly from the infected disk. This procedure, performed under general anesthesia, utilizes advanced imaging techniques to provide real-time visualization of sample collection. This sampling is the most accurate way to diagnose discospondylitis and confirm what organism is causing the infection. Due to the cost and invasiveness of the procedure, however, this test is not always recommended or performed.
How is discospondylitis treated?
Discospondylitis is treated with an appropriate antibiotic or antifungal treatment, depending on the type of infection. Treatment typically is continued for a period of 6–12 months, with long courses of medication required to clear infection. Stopping medication too early can allow the signs of discospondylitis to recur, even in a dog that was showing dramatic signs of improvement.
"Treatment typically is continued for a period of 6–12 months, with long courses of medication required to clear infection."
In many cases, X-rays are used to monitor the response to treatment. The first monitoring X-rays are typically taken 6-8 weeks after beginning antibiotics. It is important to note, however, that the appearance on X-rays often lags several weeks behind clinical improvement. Bony changes take time to occur and they take time to resolve; therefore, signs of improvement may not be obvious early in treatment.
If dogs fail to improve on medication, surgery may be recommended. Surgery allows the area to be thoroughly explored and flushed, allows for the removal of any foreign materials, and can be used to decompress the disk, alleviating pressure on the spinal cord. Additionally, surgery can allow sample collection for cultures, helping veterinarians appropriately identify the source of the infection and optimal drug treatments.
In addition to these targeted treatments, the treatment of discospondylitis typically includes pain medications. There are a variety of pain medications that can be used, depending on your dog’s pain level and overall health status. Talk to your veterinarian about the best pain medication options for your pet.
What is the prognosis for discospondylitis?
The prognosis for dogs affected with discospondylitis depends on the underlying cause of infection.
Bacterial discospondylitis often carries a good prognosis. Most cases will resolve with early and aggressive treatment, although 6–12 months of antibiotics may be required and relapses can occur.
"The prognosis for dogs affected with discospondylitis depends on the underlying cause of infection."
Brucellosis infection cannot be completely cured, but can often be successfully managed with long-term antibiotics. Most dogs with discospondylitis caused by brucellosis will require lifelong antibiotic therapy, but they can have a good quality of life.
Fungal discospondylitis has a guarded to fair prognosis. While most dogs do respond to medication, some do not. Among dogs that respond to medication, many require lifelong treatment in order to minimize signs of infection.
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