Introduction
Definition: An infectious inflammatory process of the vertebral body, often involving the adjacent intervertebral disc (Discitis).
Epidemiology: Most common in patients >50 years old.
Risk Factors:
Diabetes Mellitus.
Intravenous (IV) drug use.
Chronic corticosteroid use/Immunosuppression.
Recent invasive procedure (urological, dental, or spinal).
Endocarditis.
Etiology
Most Common Organism: Staphylococcus aureus (>50% of cases).
IV Drug Users: Pseudomonas aeruginosa.
Post-Urogenital Procedures: Escherichia coli or Proteus.
Sickle Cell Disease: Salmonella (though S. aureus is still common).
Pathogenesis
Hematogenous Spread: Most common route via the Batson’s Plexus (a valveless venous network connecting the pelvic and spinal veins).
Direct Inoculation: Post-surgical or penetrating trauma.
Contiguous Spread: From adjacent soft tissue infection (e.g., psoas abscess).
Clinical Presentation
Symptoms:
Back Pain (90%): Constant, "boring" pain, often worse at night.
Fever: Present in only ~50% of cases (absence of fever does NOT rule it out).
Physical Exam:
Point tenderness over the affected spinous process.
Paraspinal muscle spasms.
Neurological deficit (indicates epidural abscess or vertebral collapse).
Diagnostics
Laboratory Tests
ESR and CRP: Elevated in >90% of cases. CRP is more sensitive for monitoring treatment response.
Blood Cultures: Positive in 40–60% of cases. Mandatory before starting antibiotics unless the patient is septic.
Imaging
MRI: The Gold Standard (Sensitivity/Specificity >90%).
T1-weighted: Low signal in the disc and adjacent vertebral bodies (loss of endplate definition).
T2-weighted: High signal in the disc (fluid/edema).
Gadolinium: Enhancing disc and endplates.
CT-Guided Biopsy: Indicated if blood cultures are negative and MRI is suggestive.
Treatment
Non-Operative (Primary Treatment)
Indications: Most patients without neurological deficit or significant instability.
Management:
Long-term IV Antibiotics: Typically 6–12 weeks based on sensitivity.
Bracing: (TLSO) for comfort and to prevent deformity during healing.
Monitoring: Serial CRP and ESR every 1–2 weeks.
Operative
Indications:
Neurological deficit (secondary to epidural abscess or bony collapse).
Progressive spinal deformity or instability.
Failure of medical management (persistent pain or rising inflammatory markers).
Large epidural abscess.
Procedures:
Debridement and stabilization.
Anterior vs. Posterior approach depending on the location of the abscess/necrosis.
Pits & Pearls
Pearl: Disc space involvement is the hallmark of pyogenic infection. If the disc is spared but the vertebral body is destroyed, think Malignancy or Tuberculosis (Pott’s Disease).
Pitfall: Starting antibiotics before obtaining cultures. This significantly decreases the yield of a subsequent biopsy.
Tip: Always screen for Endocarditis (Echocardiogram) if a patient has pyogenic vertebral osteomyelitis, as the heart is often the primary source.
Differential Diagnosis: Pyogenic vs. Granulomatous vs. Malignancy
Feature | Pyogenic Osteomyelitis | Tuberculosis (Pott's) | Metastatic Malignancy |
Onset | Acute / Subacute | Chronic (Slowly progressive) | Chronic / Insidious |
Primary Organism/Type | S. aureus | M. tuberculosis | Lung, Breast, Prostate, Renal |
Disc Involvement | Involved Early (Discitis) | Involved Late (Disc sparing) | Spared (Disc is avascular) |
Vertebral Body | Destruction near endplates | Large "cold" abscesses | Pedicle destruction (Winking Owl) |
Deformity | Minimal unless late | Severe (Gibbus deformity) | Pathologic fractures |
Systemic Signs | Fever, High WBC/CRP | Night sweats, weight loss | Cachexia, primary tumor signs |
MRI Characteristics | High T2 signal in disc | Subligamentous spread | Low T1, High T2 in bone only |
Tuberculosis (Pott's Disease) - Key Nuances
Pathophysiology: Spread via the subligamentous route (under the ALL), which can lead to multiple skip lesions and severe kyphosis (Gibbus deformity).
Imaging: Characterized by large paraspinal abscesses (Cold Abscess) that are disproportionately large compared to the bony destruction.
Paradox: Unlike pyogenic bacteria, TB lacks the proteolytic enzymes to break down the intervertebral disc quickly, so the disc remains intact for a long time.
Metastatic Malignancy - Key Nuances
The "Winking Owl" Sign: On an AP X-ray, the destruction of one pedicle looks like the owl is winking at you.
Posterior Elements: Malignancy has a predilection for the pedicle and posterior elements, whereas infections typically start in the anterior vertebral body/disc.
Disc Integrity: Cancer cells do not cross the disc space. If you see two destroyed vertebrae with a perfectly healthy disc in between, it is almost certainly malignancy.
Pits & Pearls for the Differential
Pearl: If the MRI shows a "bright" disc on T2-weighted images, your first thought should be Pyogenic Infection.
Pitfall: Biopsying a suspected TB lesion without sending a sample for AFB (Acid-Fast Bacilli) Stain and Lowenstein-Jensen culture. Standard cultures will come back negative.
Tip: In malignancy cases, check the Pedicles. In infection cases, check the Endplates.