Discospondylitis

Introduction

Discospondylitis is an inflammatory disease affecting the intervertebral discs, vertebral endplates, and adjacent vertebral bodies in domestic animals, typically dogs and less commonly cats. The condition is often caused by bacterial or fungal infections, which can lead to spinal pain, neurological deficits, and even paralysis if not properly diagnosed and treated.

Terminology

Discospondylitis refers to inflammation involving the disc and adjacent vertebral bodies.

Epidemiology

Risk factors

Predisposition to discospondylitis is seen in large breed dogs, and certain breeds such as German shepherds and Doberman pinschers may be at increased risk². Risk factors include male sex, older age, and exposure to infectious agents or procedures that increase susceptibility to infection.

Associations

Discospondylitis often associates with genitourinary tract infections. Hematogenous dissemination from primary foci like the bladder is a common pathway for infection. Less frequently, infection starts from sites like surgical wounds, bite wounds, or migrating foreign bodies.

Clinical presentation

The condition typically presents with signs of spinal pain, fever, lethargy, and reluctance to move. Neurological deficits, such as paresis or paralysis, may manifest if there is significant spinal cord compression³. Clinical signs can be diffuse and variable, complicating diagnosis.

Pathology

Discospondylitis begins with the infection of the cartilaginous vertebral endplates and extends into the intervertebral discs. Bacteria or fungi lodge in the endplates due to localized blood flow characteristics in the vertebrae. Organisms such as Staphylococcus spp., Streptococcus spp., and Brucella canis are often involved.

Location

Lesions can be present in any spinal region, with the lumbar spine being a common location. Multiple sites along the vertebral column may be affected.

Lesions caused by migrating foreign bodies, such as grass awns, tend to localize in the lumbar spine after penetrating the retroperitoneal space. These may be associated with Actinomyces spp. infections.

Genetics

There is no specific genetic component identified, but breed predispositions suggest genetic or conformational factors might contribute to susceptibility. Predisposed breeds include Great Danes, boxers, Rottweilers, German shepherd dogs, and Doberman pinschers. Dog breeds with predisposition to systemic fungal disease (eg. Aspergillosis), such as German shepherds and Rhodesian ridgebacks may also have intervertebral disc involvement.

Cats are rarely affected with discospondylitis, but it may be seen if adjacent to a wound. Cattle and other species may also be affected.

Radiographic features

Imaging plays a vital role in diagnosing discospondylitis. Changes such as narrowing or widening of the intervertebral space, endplate irregularities, and vertebral lysis can be noted. Common features include:

• Symmetric lysis of adjacent vertebral endplates, shortening of vertebrae

• Narrowing of the intervertebral disc space

• Periosteal reaction on ventral and lateral vertebrae may be irregular or aggressive, eventually bridging the two vertebral bodies

• Sclerosis of vertebral body adjacent to lysis

• Focal or multifocal distribution, multifocal lesions may be in different stages of chronicity

MRI

MRI is superior to radiography at identifying soft tissue components and degree of involvement in discospondylitis. Using MRI, discospondylitis can be detected earlier than with radiographs alone.

Structural deficits include lysis of the vertebral endplates and subluxation of adjacent vertebrae.

Signal characteristics for:

T1

• Hypointensity of affected endplates and bone marrow.

T1+C

• Contrast enhancing tissues in the intervertebral disc space, vertebral end plates and surrounding area.

• Enhancing tissue (empyema) may extend into spinal canal and cause spinal cord compression.

T2

• Hypointense vertebral endplates and adjacent bone marrow. STIR hyperintensity of these areas.

• Hyperintense disc

• Hyperintense bone marrow prior to endplate erosion (early lesion)

Radiology report

Morphology

• Describe the degree of disc space narrowing or expansion and endplate erosion.

• Describe the periosteal reaction

Relationship to/involvement of

• Report any involvement and extent of infection in the paravertebral soft tissues.

Extension

• Note the affected sites and stages of chronicity

• Note any vertebral subluxation or potential for spinal cord compression.

Treatment and prognosis

The treatment involves prolonged antibiotic or antifungal therapy depending on cultured organisms. In addition to medical therapy, restricted movement followed by gradual re-introduction of activity is recommended to prevent complications.

Complications

Potential complications include spinal cord compression due to vertebral subluxation or abscess formation and sequelae from concurrent disorders like urinary tract infections.

History and etymology

The term discospondylitis etymologically suggests inflammation (itis) of the discs (disco) and vertebrae (spondyl). The term reflects the dual involvement of these structures typically seen in infection.

Differential diagnosis

The imaging characteristics of discospondylitis are very specific and are usually definitive. If no endplate lysis is visible, possible differential diagnoses include intervertebral disc disease, tumor, or trauma. The distinctions are made based on clinical presentations, imaging findings, and laboratory results.

Practical points

• Always include the entire spine in radiographic studies to assess the full extent of disease.

• Consider blood and urine cultures when discospondylitis is suspected.

• MRI is preferred over radiography for early detection and detailed assessment of discospondylitis.