Feline Discospondylitis Study Guide

Overview and Clinical Importance

Discospondylitis (also spelled diskospondylitis) is an infection of the intervertebral disc and adjacent vertebral endplates, typically bacterial or fungal in origin. While considerably more common in dogs, feline discospondylitis is rare but clinically important and appears on NAVLE examinations as part of differential diagnosis for spinal pain and neurological dysfunction in cats.

The condition results from infection of the intervertebral disc space (discitis) and adjacent cartilaginous vertebral endplates (spondylitis). In cats, the lumbosacral junction (L7-S1) is most commonly affected, accounting for approximately 36-50% of all feline cases. Recognition of this condition is essential because early diagnosis and appropriate antimicrobial therapy typically result in favorable outcomes.

Etiology and Pathophysiology

Routes of Infection

The exact route of infection is often unknown in individual cases. The following mechanisms have been implicated in feline discospondylitis:

• Hematogenous spread (most common): Bacteria enter the bloodstream from a distant site (urinary tract, oral cavity, skin wounds) and travel to the vertebral endplate capillary beds where sluggish blood flow allows bacterial seeding
• Direct inoculation: Cat bite abscesses (especially at the tail base), penetrating trauma, or iatrogenic causes from spinal surgery or epidural injections
• Direct extension: Spread from infected paravertebral structures or adjacent abscesses
• Migrating foreign bodies: Less common in cats than dogs; plant awns (grass seeds) may migrate toward the vertebral column

Pathophysiology Mechanism

Blood supply within the vertebral endplates consists of capillary beds with reduced blood flow velocity. Pores in the endplate that normally allow nutrient diffusion also provide a route for organisms to enter the intervertebral disc. The minimal vascular supply of the disc perpetuates infection once established. The sequence includes:

• Organisms enter via arterial blood supply to vertebral endplate
• Bacteria localize in venous channels (sluggish flow)
• Infection spreads through diffusion to avascular disc
• Inflammation and bacterial growth cause necrosis
• Erosion of vertebral endplates creates lytic lesions
• Potential complications: vertebral instability, disc collapse, spinal cord/nerve root compression

Causative Organisms in Feline Discospondylitis

Signalment and Clinical Presentation

Signalment

Clinical Signs

Cardinal Sign

Spinal hyperaesthesia (100% of cases) - This is the hallmark of feline discospondylitis and is ALWAYS present. Pain on palpation of the affected spinal region is universally found. In 35.3% of cases, this is the only neurological sign present.

Neurological Signs (64.7% of cases)

Non-Specific Clinical Signs

• Reluctance to jump (52.9%)
• Lethargy (41.2%)
• Inappetence/anorexia (23.5%)
• Pyrexia (17.6%) - Temperature greater than or equal to 39.2°C; notably UNCOMMON
• Dysuria (11.8%)
• Obstipation/megacolon (5.9%)

Neurolocalization by Lesion Site

Diagnosis

Laboratory Findings

Important: Laboratory abnormalities are typically inconsistent and non-specific in feline discospondylitis. Normal results do NOT rule out the disease.

Bacterial Culture Results

Cultures are positive in only 11.8% of feline cases. This low yield is similar to dogs (40-75% negative cultures). Despite this, cultures should ALWAYS be submitted because identification of the organism guides targeted antimicrobial therapy.

• Urine culture: Submit in ALL cases (11.8% positive)
• Blood culture: Consider if febrile; 12.5% positive
• Fine-needle aspirate (FNA) of disc: CT or fluoroscopy-guided; 33% positive (intradiscal); highest yield

Diagnostic Imaging

Imaging is CRITICAL for diagnosis given the variable and non-specific clinical presentation. MRI is the gold standard, though radiography remains an important screening tool.

Radiography

Limitations: Radiographic changes may lag 2-4 weeks behind clinical signs. A normal radiograph does NOT rule out discospondylitis early in disease. Repeat radiographs in 1-2 weeks if initial study is negative but clinical suspicion remains high.

Radiographic Findings:

• Intervertebral disc space narrowing or collapse (80%)
• Vertebral endplate erosion/osteolysis (60%)
• Sclerosis of adjacent vertebral bodies
• Spondylosis deformans (bony bridging)
• Loss of normal endplate morphology

MRI Findings (Gold Standard)

MRI is more sensitive than radiography, especially in early disease. Characteristic findings include:

Differential Diagnosis

For cats presenting with spinal pain and/or neurological deficits, consider:

Treatment

Antimicrobial Therapy

Medical management is the mainstay of treatment. All feline cases in the literature have been managed non-surgically. Empirical antibiotic therapy is typically initiated before culture results are available (given low yield).

Analgesic Therapy

Pain management is essential and should be provided to ALL patients:

Supportive Care

• Exercise restriction: Strict cage/room rest for minimum 4 weeks; avoid jumping and stairs
• Nursing care: Padded bedding; assistance with urination/defecation if needed
• Monitoring: Clinical improvement expected within 3-5 days of starting antibiotics; if no improvement, consider resistant organism or fungal infection

Surgical Intervention

Surgery is rarely indicated in cats. Consider surgical intervention only for: severe neurological deficits unresponsive to medical therapy; vertebral instability; pathological fractures; spinal cord compression from epidural abscess; and obtaining tissue for culture/biopsy if medical management fails.

Prognosis and Outcome

Overall prognosis is FAVORABLE with appropriate treatment. In a study of 17 cats with outcome data available for 12:

• Excellent outcome: 83.3% (10/12 cats) - complete resolution of pain and neurological function
• Relapse: 8.3% (1/12) - occurred after only 6 weeks of single antibiotic treatment
• Poor outcome (euthanasia): 8.3% (1/12) - failed to respond during hospitalization

Key prognostic factors:

• Early diagnosis and initiation of treatment
• Duration of antibiotic therapy (minimum 3 months recommended)
• Severity of neurological deficits at presentation
• Presence of comorbidities (chronic kidney disease, endocarditis)

Memory Aid

DISCO = Feline Discospondylitis

• D = Disc infection (intervertebral disc + endplates)
• I = Imaging essential (MRI gold standard)
• S = Spinal pain ALWAYS present (100%)
• C = Cultures often negative (88%)
• O = Outcome favorable with 3 months antibiotics

Key Numbers to Remember:

• 100% = spinal hyperaesthesia present
• 17.6% = pyrexia (fever is UNCOMMON)
• 11.8% = positive cultures
• 36-50% = L7-S1 location
• 3 months = minimum antibiotic duration
• 83% = excellent outcome