Diskospondylitis is an infection of the intervertebral disc and adjacent bones (vertebral endplates). Some patients may have disease at multiple sites along the spine. Most commonly, the infection comes from the skin or urinary tract and spreads by blood or lymph. Rarely, infections can come from trauma such as a migrating grass awn or surgery. Frequently infections are bacterial but fungal diskospondylitis may occur, and some breeds like German Shepherd dogs may be at an increased risk.
The most common sign of diskospondylitis is sudden onset of pain. Your pet may show this by carrying their head low, not turning their head or neck, having an arched back, and/or crying out while moving. Lethargy and general disinterest in activities are also common due to the persistent discomfort. Some animals may be reluctant to eat. Fevers are rare.
When the infection has spread into the spinal canal or has destroyed enough disc and bone to cause a disc herniation or fracture, additional neurologic deficits may occur. In addition to being painful, these patients may drag their paws, have a wobbly gait, or even be paralyzed. Progression from pain to having neurological impairment is often referred to as ‘complicated diskospondylitis.’
Frequently diskospondylitis can be diagnosed on an x-ray (radiograph). Even if your pet only has back pain, often full spinal x-rays including the neck and back are recommended to look for additional sites of infection (lesions). The most affected site is in the low back (L7-S1) and the neck is overall less commonly affected.
Sometimes x-ray changes will lag behind the onset of symptoms and will not show definitive abnormalities. MRI and/or CT have increased sensitivity and can be helpful when x-rays are normal. MRI and/or CT are also commonly recommended if there is concern for complicated diskospondylitis. These advanced imaging techniques not only aid in providing a definitive diagnosis but can help determine if surgery is indicated. They will allow better assessment and surgical planning for fractures, disc herniations, and empyema (spinal abscess).
In addition to confirming the presence of infection with imaging studies, additional testing is needed to determine the nature of the infection. Blood and urine cultures are recommended in every patient. Brucellosis is a reportable disease because it has the potential to spread from animals to people and can have devastating effects. For this reason, brucella testing is recommended in all canine patients. Although intact animals are thought to be at higher risk for brucellosis, neutered animals may be infected, especially in the southeast and should still be tested. Fungal testing on a blood or urine samples is performed in at-risk animals such as German Shepherds or immune-compromised patients, such as those on chemotherapy or treatment for autoimmune disease (e.g., auto-immune hemolytic anemia, meningoencephalitis of unknown origin). Fungal diskospondylitis is uncommon but your neurologist will recommend appropriate testing based on your geographic location and/or travel history.
Blood, urine, brucella, and fungal testing can be normal in 20-80% of patients. Sometimes empirical (best-guess) treatment will still be effective. Other times more invasive sampling techniques may be recommended to determine the type of infection and choose appropriate anti-microbial drugs. This can be done with x-ray or CT-guided disc aspirates, where a needle is inserted through the skin and into the disc space to obtain a sample. Biopsy and cultures can also be obtained through surgery, though this is usually reserved for refractory cases or those that require surgery for other reason (fracture, disc herniation, empyema).
While the infectious disease tests and cultures are pending (they can take a several days), empirical broad-spectrum antibiotics for the most common infections may be started. Pain medications (analgesics and/or anti-inflammatories) may also be prescribed. The results of infectious disease testing will determine what the best anti-microbial drug is. Most patients with diskospondylitis will need a minimum of 3 months of anti-microbial treatment. In one study, the average treatment time was 12 months. Repeat x-rays every 4-8 weeks are used to guide the duration of treatment. Once x-rays show lack of continued bone destruction, anti-microbial therapy will usually be discontinued a month later. The tissues will not return to normal on x-rays but should show evidence of scarring or sclerosis.
For cases of complicated diskospondylitis surgery may be recommended. Surgery is typically reserved for patients who have severe empyema (spinal abscess), an unstable fracture/luxation, or have severe neurologic deficits (are unable to walk). Surgery carries risk of causing further instability as well as potential problems if spinal implants must be placed into infected bones. Your Veterinary Neurologist will review any potential complications with you if surgery is necessary for your pet.
Most patients with non-resistant bacterial infections and no neurological deficits have a good prognosis and will respond quickly to appropriate antimicrobial treatment. Patients with brucella are considered infected for life, despite antimicrobial therapy, and present continued risk to human health. Fungal diskospondylitis is also thought to have a more guarded prognosis but there is little long-term information available. If the fungal infection is wide-spread throughout your pet’s body, the prognosis is quite guarded.
Although surgery has significant risks, cases of complicated diskospondylitis that require surgery can still do quite well (>80% success).
It is uncommon for cats to be diagnosed with diskospondylitis. No specific risk factors have been identified and diagnosis and treatment is similar to dogs. Cats may respond to treatment quicker than dogs with one study showing an average treatment time of 3 months in cats. Overall, the prognosis is good for cats with diskospondylitis.