Discospondylitis

What is discospondylitis?

Discospondylitis is a bacterial or fungal infection of the intervertebral discs and the adjacent vertebral bones in the back. Intervertebral discs lie between vertebrae in the vertebral column (spine or backbone). Discospondylitis may occur at one 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, with only a few reported cases.

What causes discospondylitis?

Discospondylitis occurs when bacteria or fungi reach the intervertebral discs. There are several ways that this can happen.

Hematogenous (blood-borne) spread. Bacteria or fungi enter the bloodstream through a wound or infection. Blood flows through the intervertebral disc space, which allows the bacteria or fungi to be deposited, leading to infection. This is the most common source of discospondylitis.

Direct contamination. Bacteria or fungi are deposited directly adjacent to the disc. Direct contamination is typically associated with a deep bite or puncture wound directly over the spinal column, although it may also result from surgical procedures that involve the spine.

Migrating foreign body. Foreign material (e.g., 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 the condition. 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?

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 seem to be in pain 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.

The signs of discospondylitis often begin gradually and progress slowly over time. Many affected dogs, though not all, also show non-specific signs such as fever, decreased appetite, weight loss, and lethargy.

How is discospondylitis diagnosed?

Discospondylitis is often diagnosed using spinal X-rays. Although the disc itself cannot be seen on an X-ray, discospondylitis causes changes in the bony vertebrae adjacent to the affected disc. These changes become visible on X-ray three 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, such as myelography (imaging involving dyes), CT scan, MRI, or bone scintigraphy (imaging involving radioactive tracers). Although these tests are expensive and typically require a referral to a specialist, they are far more sensitive than X-rays for discospondylitis.

If testing suggests discospondylitis, your veterinarian may perform additional tests to confirm the type of infection. This testing allows your veterinarian to prescribe the most appropriate treatment. The tests may include blood and/or 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, bacterial and fungal organisms, and other laboratory parameters.

In some situations, a neurologist may attempt to obtain a culture directly from the infected disc. This procedure, performed under general anesthesia, uses advanced imaging techniques to provide real-time visualization of sample collection. This sampling is the most accurate way to diagnose discospondylitis and confirm which 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 is typically continued for a period of 6–12 months, with long courses of medication required to clear the infection. Stopping the medication too early can allow the signs of discospondylitis to recur, even in a dog that was showing dramatic signs of improvement.

In many cases, X-rays are used to monitor the response to treatment. The first monitoring X-rays are typically taken six to eight 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 your dog fails 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 disc, 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. This surgery is performed by a specialist.

In addition to these targeted treatments, treating discospondylitis typically includes pain medications. A variety of pain medications 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 resolve with early and aggressive treatment, although 6–12 months of antibiotics may be required, and relapses can occur.
• Brucellosis infection cannot be completely cured but can often be successfully managed with long-term antibiotics. Most dogs with discospondylitis caused by brucellosis require life-long antibiotic therapy, but they can have a good quality of life.
• Fungal discospondylitis has a guarded (uncertain) to fair prognosis. While most dogs do respond to medication, some do not. Among dogs that respond to medication, many require lifelong treatment to minimize signs of infection.