Neurosurgery notes/Infection/Spinal infection/Pyogenic Spondylodiscitis

Pyogenic Spondylodiscitis

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Spinal infection
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Brucella pyogenic spondylodiscitis

General

  • The following are various manifestations of the same underlying disease process of spinal infection.
    • Spondylodiscitis
    • Discitis
      • Infection of the nucleus pulposus.
      • May start in the cartilaginous endplate and spread to the disc and vertebral body (VB).
    • Spinal osteomyelitis
      • Primarily involves the VB and spreads secondarily to the disc space.
    • Epidural abscesses

Aetiology/Classification

  • Primary infection
    • Primary or de novo spinal infections (DNSIs):
      • Occur spontaneously in an unoperated spine.
      • Emphasize truly spontaneous/natural origin (not only hematogenous, but any natural occurrence).
    • Native vertebral osteomyelitis (NVO):
      • Occur spontaneously in an unoperated spine.
      • Most commonly due to hematogenous spread from a distant infectious source.
  • Secondary infections after spinal interventions:
    • Develop as complications following spinal surgery, instrumentation, or other procedures.
    • Typically arise from local inoculation during the procedure.

Juvenile

  • Age: Usually < 20 years (peak between 2-3 years)
  • Pathophysiology:
    • Due to the presence of primordial feeding arteries that nourish the nucleus pulposus and which involute at ≈ 20–30 years of age.
  • Spinal level:
    • Lumbar spine most common
  • Clinical Features (Juvenile)
    • Refusal to walk or stand progressing to refusal to sit
    • Back pain is most common in children > 9 years of age
    • Low-grade fever may be present
    • ESR is usually 2–3× normal
    • WBC is sometimes elevated
    • Rare to get neurological deficit
  • Microorganism (Juvenile)
    • H. influenzae is a more commonly seen pathogen in this group
  • Natural History (Juvenile)
    • In most cases, there is complete resolution in 9–22 weeks without recurrence in long-term follow-up studies.
  • Treatment (Juvenile)
    • Surgery
      • Rarely needed
      • Indications:
        • Infective progression in spite of antibiotics
        • Spinal instability
        • Recurrent cases
  • Antibiotics
    • Indication
      • Positive cultures (blood cultures or biopsy cultures)
        • Elevated WBC count, constitutional symptoms, or high fever
        • Poor response to rest or immobilization
        • Neurologic sequelae (very rare)
    • Duration: 4–6 weeks
    • Start with IV antibiotics, when clinical symptoms improve, convert to PO for the remainder of therapy

Adult

Numbers

  • Incidence: Approximately 4.8 per 100,000 patients in the United States
  • Gender: Men are affected more commonly than women

Risk Groups

  • Bimodal distribution:
    • Older/sicker patients with comorbidities AND
    • Younger patients with IV drug use
      • IV drug users and patients with HIV are known to develop spondylodiscitis with specific organisms
  • Increasing prevalence due to rising number of predisposing conditions
    • Diabetes
    • Alcoholism
    • Malignancy
    • Chronic steroid usage
    • Renal failure
    • Cirrhosis
    • Sickle cell disease
    • Chronic vascular access (dialysis)
    • Urinary tract infection (UTI)
    • Distant infective focus
    • Recent bloodstream infection

Location

  • Lumbar spine: 58% (most frequently involved due to relative blood flow)
  • Thoracic spine: 30%
  • Cervical spine: 11%

Pathophysiology

  • Arterial spread: most common route
    • Nearly 30% of all hematogenous spinal infections are associated with concomitant bacterial endocarditis
  • Retrograde venous spread: can occur from pelvic organ or retroperitoneal infections
  • Direct inoculation during spine surgery or interventions: accounts for 20% of spinal infections

Mortality

  • Even with appropriate care, these infections have a mortality rate of up to 20%

Clinical Presentation

General

  • Often a delay in the diagnosis of pyogenic spondylodiscitis because
    • Presentation can be insidious.
    • The initial presentation can be nonspecific with a variable degree of constitutional symptoms.
    • Therefore, a high index of suspicion must be maintained, especially in dealing with susceptible patient populations.

Symptoms

  • Pain (the primary symptom)
  • Local pain:
    • Usually well-localized to the level of involvement
    • Moderate to severe
    • Exacerbated by virtually any motion of the spine
    • Night pain is a hallmark characteristic
  • Radiation patterns:
    • Abdomen
    • Hip
    • Leg
    • Scrotum
    • Groin
    • Perineum
  • Radicular symptoms:
    • Occurs in 50% to 93%
  • Fever and chills:
    • Up to 70% are afebrile
    • Constitutional symptoms: malaise, anorexia, weight loss
  • Neurological manifestations:
    • Some patients present with radiculopathy, numbness, deformity
    • Incomplete/complete paralysis with bladder or bowel involvement
  • Painless spondylodiscitis can be seen particularly in IV drug users or cirrhosis (Pseudomonas and E. coli)
    • this type carries high mortality
  • Sepsis: A notable subset of patients may present with toxic symptoms and septic shock

Signs

  • Localised tenderness over the involved region
  • Paravertebral muscle spasm
  • Limitation of movement
  • Varying neurological deficits depending on level of compression (from root-level deficit to complete spinal cord involvement)
  • Compression of sacral roots may result in cauda equina–like picture
  • Cervical retropharyngeal abscess can present with dysphagia and dyspnea
  • Lumbar psoas abscesses can present with flank pain, abdominal discomfort, and heaviness
  • Rarely: palpable subcutaneous abscess or discharging sinus

Investigation

Blood Tests

  • Complete Blood Count (CBC)
  • WBC (White Blood Cell count):
    • Peripheral WBC is often normal
    • Rarely elevated above 12,000
  • Inflammatory Markers
    • ESR (Erythrocyte Sedimentation Rate):
      • In non-immunocompromised patients, ESR will be elevated in almost all cases
      • Average value: 60 mm/hr
      • ESR can be normal in discitis (rare occurrence but should call diagnosis into question)
      • Useful to follow as an indicator of response to treatment
      • Expected drop of approximately 50% per week with adequate response to treatment
    • C-reactive Protein (CRP):
      • Often used in conjunction with ESR
      • Sensitive marker for monitoring treatment response
      • Expected drop of approximately 50% per week with adequate treatment
      • Important for monitoring: improvement in imaging often lags behind improvement in clinical and laboratory markers
  • Blood Cultures
    • Initial approach:
      • Three blood cultures are recommended to maximize yield
      • Can identify the organism in up to 60% of cases
      • Should be obtained before starting antibiotics when possible
    • Prognostic value:
      • History of bloodstream infection with Staphylococcus aureus in past 3 months in a patient with spondylodiscitis has high predictive value for S. aureus infection in the spine
  • PPD (Purified Protein Derivative)
    • AKA Mantoux screening test
    • May be helpful to rule out Pott’s disease in cases of spontaneous discitis
    • May be negative in 14% of cases

Radiological Investigation

Plain X-rays

  • Usually not helpful for early diagnosis
  • At least 30% bone destruction is required for infective lesions to be picked up on plain radiographs
  • Sequence of radiographic changes:
    • Earliest changes (Not seen <2–4 weeks following onset, nor later than 8 weeks):
      • Interspace narrowing with some demineralization of the VB
    • Early progression (starting 4–12 weeks following onset):
      • Sclerosis (eburnation) of adjacent cortical margins
      • Increased density of adjacent areas of VB representing new bone formation
    • Progressive changes:
      • Irregularity of the adjacent vertebral endplates
      • Sparing of the pedicles (exception: tuberculosis may involve the pedicles)
      • In 50% of cases: infection remains confined to disc space
      • In other 50%: spreads to adjacent VB
    • Late findings (6–8 months into course):
      • Widening (ballooning) of disc space with erosion of VB
      • Circumferential bone formation may lead to exuberant spur formation
      • Spontaneous fusion of VB may occur

CT and

  • Features
    - Can rule out paravertebral or epidural spinal abscess
    - Better for assessing bony fusion and integrity
    - Poor for demonstrating canal compromise
  • Diagnostic Criteria on CT (If present, indicates discitis):
    • The three basic changes are:
      • Endplate fragmentation
      • Paravertebral soft-tissue swelling with obliteration of fat planes
      • Paravertebral abscess
    • All 3 present = Pathognomonic for discitis
    • Only first 2 present = 87% specific for discitis

CT-myelogram

  • Good at assessing spinal canal for compromise

PET-CT

  • PET-CT has emerged as an additional diagnostic modality for patients in whom MRI is not feasible.

MRI (Spinal MRI with Contrast)

  • Status:
    • Benchmark test to diagnose spondylodiscitis (gold standard)
  • Features:
    • Demonstrates involvement of disc space and of VB
    • Good at ruling out paravertebral or epidural spinal abscess
    • Poor at assessing bony fusion and bone integrity
    • As sensitive as radionuclide bone scan
    • Can provide clues to differentiate pyogenic spondylodiscitis from tubercular spondylodiscitis
  • Characteristic findings (may occur 3–5 days after onset of symptoms):
    • T1: Decreased signal from the disc and adjacent portion of VBs
    • T2: Increased signal from these structures
    • Enhancement is common
  • Classical lesion for pyogenic spondylodiscitis:
    • Paradiscal lesion with disk involvement
    • Destruction of two contiguous end plates adjacent to the disk
    • Abscess formation and soft-tissue thickening
  • Important:
    • Perform MRI of the entire spine because skip lesions are common

Nuclear Medicine (Radionuclide Scanning)

  • Sensitivity:
    • Very sensitive for discitis and vertebral osteomyelitis (85% sensitivity)
  • Limitation:
    • May be negative in up to 85% of patients with Pott’s disease
  • Agents used:
    • Technetium-99 (abnormal as early as 7 days following onset of clinical symptoms) OR
    • Gallium-67 (abnormal within 14 days)
  • Positive scan findings:
    • Focal increased uptake in adjacent endplates
    • May be differentiated from osteomyelitis which will involve only one endplate
    • Important caveat: A positive scan is not specific for infection and may also occur with:
      • Neoplasms
      • Fractures
      • Degenerative changes

Cultures and Biopsy

  • CT-Guided Biopsy
    • Status: Investigation of choice to identify causative organism when nonsurgical line of treatment is planned
    • Culture sensitivity:
      • Local cultures can identify organism in up to 80% of cases
      • Higher sensitivity from biopsy of disk and paravertebral soft tissues than bone and endplate
      • No notable difference in microbiology sensitivity between patients who did and did not receive antibiotics before biopsy
    • Technique note: Surgery for open biopsy alone is usually not indicated
  • Blood Cultures
    • Yield: May be positive in ≈ 50% of cases
    • Clinical use: Can be helpful in guiding choice of antimicrobial agent when positive
    • Notable agreement:
      • There is notable agreement between growth in blood culture and tissue cultures
      • Recommend starting antibiotics on the basis of blood cultures before tissue cultures are obtained
  • Tissue Culture
    • Staining: for acid-fast bacilli (AFB) to identify Mycobacterium tuberculosis (TB) should be done in all cases

Microbiology

Primary pathogens in pyogenic spondylodiscitis

  • Staphylococcus aureus:
    - Most common organism overall when direct cultures are obtained
    - Most common isolate, with MRSA in up to 40% of cases
    - Other staphylococcus species: S. albus, S. epidermidis
  • Gram-negative organisms:
    - E. coli and Proteus species
    - Pseudomonas aeruginosa (commonly in IV drug abusers)
    - E. coli is most common in immunocompromised patients

Organism-specific considerations

Brucella pyogenic spondylodiscitis
  • IV drug abusers: Skin flora (S. aureus including MRSA, S. epidermidis, Pseudomonas) are most prevalent
  • Infectious endocarditis: Streptococcus viridans and group D streptococci must be considered
  • Sickle cell disease: Salmonella must be considered
  • Juvenile discitis: H. influenzae is more commonly seen
  • Tuberculous spondylitis (Pott’s disease): Mycobacterium tuberculosis

Management

Non-Operative Treatment

Bracing

  • Outcome is generally good, and antibiotics together with spinal bracing (immobilization) are adequate treatment in ≈ 75% of cases.
  • Most patients are started on strict bed rest, and are then mobilized with or without a brace as tolerated.
  • Effect on outcome: Probably does not affect final outcome, but:
    • Affords earlier pain relief for some
    • May allow return to activity at an earlier time
  • Duration:
    • 6-8 weeks
  • Types of bracing:
    • Thoracic or upper lumbar discitis: Patient is fitted with clamshell-type body jacket
      • Most patients find discomfort from the brace worse than without it
    • Alternative forms of immobilization:
      • Spica cast (provides better immobilization for lower lumbar discitis)
      • Corset-type brace (less immobilization but better tolerated)

Antibiotic Management

  • Duration of Antibiotic Therapy
  • Minimum duration: At least 6 weeks of IV antibiotics
    • Duration adjustment: May need to be extended based on treatment response
      • Treat with IV antibiotics for an arbitrary period of time, usually ≈ 4–6 weeks, followed with oral antibiotics for an additional 4–6 weeks
      • Treat with IV antibiotics until the ESR normalizes, then change to PO
  • Timing
    • If stable antibiotics should be delayed until cultures have been obtained.
    • If patient presents in sepsis or with neurological deficits, empiric antibiotics may need to be started without delay.
      • Empiric Antibiotic Coverage
        • Initial antibiotic therapy should cover for:
          • MRSA
          • Gram-negative organisms (e.g., E. coli, Pseudomonas)
        • Common regimen: Combination of vancomycin and third/fourth-generation cephalosporin
  • Antibiotic option
    • Discuss with Infectious Disease team
    • Choice of antibiotics is guided by:
      • Results of direct cultures when positive
      • Positive blood culture results
      • In 40-50% of cases where no organism is isolated: broad spectrum antibiotics should be used
  • Monitoring Treatment Response
    • Clinical assessment:
      • Resolution of clinical signs and symptoms
    • Laboratory monitoring:
      • Normalisation of laboratory markers, particularly:
        • Erythrocyte sedimentation rate (ESR)
        • C-reactive protein (CRP)
        • Compare with baseline values
        • CRP is sensitive marker with expected drop of approximately 50% per week with adequate response
    • Imaging follow-up:
      • Repeat imaging is reserved for patients who fail to show improvement in clinical or laboratory parameters
      • Improvement in imaging often lags behind improvement in other clinical markers such as pain and inflammatory laboratory markers

Surgical Treatment

General

  • Surgical treatment may reduce morbidity and mortality over conservative treatment of pyogenic spondylodiscitis.

Goals of Surgery

  • Débridement of the disk space and end plate to achieve infection control
  • Neural decompression
  • Stabilization
  • Deformity correction
  • Reconstruction to achieve arthrodesis

Indications

Scoring Systems and Prediction Models to Guide Treatment
  • SISS (Spinal Instability Spondylodiscitis Score)
    • Proposed scoring system for guiding surgical decision-making
  • SITE Score (Spinal Infection Treatment Evaluation Score)
    • Performance: Higher sensitivity, specificity, and predictive value than SISS with respect to surgical recommendations
    • Emerging as the more useful scoring system
  • MSI-20 Score (Mortality in Spinal Infection)
    • Purpose: Devised to predict which patients were too sick to be offered surgery
    • Interpretation:
      - Patients with score ≥ 11: Small subgroup of patients who were too sick to undergo surgery, with high mortality rate with or without surgery
      - Patients with MSI score < 11: Early surgery recommended for all other spondylodiscitis patients

Timing of surgery

  • Early surgery for fit patients
    • Notable finding: No increase in mortality in patients treated surgically compared with patients treated conservatively, although surgically treated patients had more comorbidities and more severe disease.
  • The “Delayed Surgery” Principle for Critically Ill (10 to 14 days)
    • Important international multicenter study (Kramer et al, 192 critically ill patients):
      • Delayed surgery (after 3 days of optimization) markedly reduced mortality compared with:
        • Immediate surgery (within 3 days of presentation)
        • Conservative treatment
      • Patient characteristics: All patients were critically ill with:
        • CRP > 200 OR
        • Presence of at least two of four criteria for systemic inflammatory response syndrome upon admission
      • Additional benefits of delayed surgery:
        • Shorter hospital stay
        • Shorter intensive care unit (ICU) stay
  • Evidence
    • Recent retrospective studies have found that early surgery was associated with:
      • Reduced morbidity
      • Reduced mortality
      • Reduced length of hospital stay for these debilitating infections

Surgical options

Fixation and interbody fusion
  • Decision-making depends on:
    • Spinal level (cervical, thoracic, lumbar)
    • Extent of bony involvement
    • Pattern of disease
Cervical Spondylodiscitis
  • Primary approach:
    • Most commonly treated anteriorly with or without an additional posterior approach because the infected body and disk can be directly approached anteriorly
  • Decision-making
    • Endplate erosions:
      • Early discitis with preserved endplates: Anterior cervical discectomy and fusion (ACDF) may be appropriate
      • Advanced discitis with extensive bony erosions: Corpectomy to rest cage on stable end plate (often means two-level corpectomy because discitis involves two adjacent end plates)
    • Additional posterior fixation:
      • If two or more level cervical corpectomy is performed, additional posterior fixation is recommended to prevent:
        • Subsidence
        • Kyphosis
        • Implant failure
    • Upper cervical infections: Generally require occipitocervical fixation for stabilization in addition to débridement and biopsy
Thoracic and Lumbar Spondylodiscitis
  • Posterior Surgery
    • Status: Posterior surgery is currently most commonly performed to débride and reconstruct infection site, as well as place spinal instrumentation
    • Approaches:
      • Thoracic spine: Costotransversectomy, transpedicular, or transfacetal approach
      • Lumbar spine: Transforaminal approach
    • Advantages of posterior approach:
      • Provides robust pedicle screw fixation
      • Excellent deformity correction
      • Ability to achieve satisfactory decompression and reconstruction
      • More familiar approach for most surgeons
      • Involves less surgical time
      • Less approach-related morbidity
      • Single-approach surgery through which all goals of surgery can be achieved with markedly less approach-related morbidity
    • Outcome: DWG Registry Study group and other studies found no additional benefit of débridement and interbody cage placement over posterior instrumentation alone in surgical treatment of infective spondylodiscitis
      • Technical Approach: Transfacetal/Transpedicular
      • Procedure:
        • Exposure and pedicle screw placement
        • Two-level laminectomy performed for single-level disease
        • Pedicle tracts made on both sides
        • Temporary rod placed on one side
        • Transverse process, inferior articular facet, and superior articular facet excised using burr (rib head preserved)
        • Pedicle walls taken down using rongeur and burr to expose vertebral body and disk
        • Nerve root (T3-T11 levels) above pedicle ligated and cut to expose superior vertebral body
        • This corridor provides window for débridement, ventral decompression, and cage placement
      • For more extensive reconstructions:
        • Same corridor can be replicated at 2-3 adjacent levels with rib head excision for wider access
      • Cage placement options:
        • Static or expandable mesh cage inserted through corridor
        • Placement not always necessary
        • Defect may be left open or packed with graft depending on size of void
      • 360-degree exposure: Transfacetal approach can be performed on opposite side
    • Pedicle screw fixation extent:
      • Long-level fixation with two levels above and two levels below recommended
      • Exclude the infected vertebrae
      • In lumbar spine: Fewer fixation points may be used to preserve motion
  • Anterior Surgery
    • Less used now a days becauses
      • Associated additional approach-related morbidity (respiratory complications, ileus)
      • Particularly problematic in elderly and debilitated patient group
      • Challenging in upper thoracic spine
      • Better alternatives (posterior approaches) now available
    • Used in the past as anterior approach was provides direct access to infected disk and vertebral body, allowing for aggressive débridement and reconstruction
  • Combined Anterior-Posterior surgery
    • Less used now a days
    • Indication: Still popular in many centers for aggressive débridement and reconstruction with expandable mesh cages
      • Severe cases:
        • Combined anterior-posterior approach recommended for severe cases with large anterior defects, with better reconstruction of sagittal profile.
        • However, cage subsidence and loss of sagittal correction may occur at follow-up.
    • Comparative outcomes vs posterior only surgery
      • Clinical and radiological outcomes including fusion after all-posterior approach similar to combined anterior-posterior approach for infective spondylodiscitis
Stabilization without aggressive débridement
  • Recommended, especially in elderly patients with multiple comorbidities
Laminectomy alone without instrumentation
  • DO NOT PERFORM
  • may lead to worsening due to added instability in spondylodiscitis
Minimally Invasive Techniques
  • Benefits:
    • Minimally invasive spinal surgery has been beneficial in reducing:
      - Pain
      - Blood loss
      - Surgical time
      - Hospital stay over classical open surgery in pyogenic spondylodiscitis
  • Specific techniques:
    • Endoscopic Spine Surgery
      • Usefulness: Useful technique in spondylodiscitis for:
        - Debulking the infection
        - Taking samples for diagnostic purposes
    • Lateral Interbody Fusion Techniques
      • Approaches used for débridement and reconstruction in lumbar spondylodiscitis:
        - Extreme lateral interbody fusion
        - Oblique lateral interbody fusion

Implants in Spondylodiscitis

  • Interbody materials that are safe to use
    • Implants (titanium and PEEK)
      • General
        • Titanium and PEEK cages are preferred over structural grafts for ventral reconstruction because of high rates of subsidence and graft failure with latter
      • Titanium
        • Characteristics:
          - Most common material used for screw and cage instrumentation in spondylodiscitis
          - Resistant to biofilm formation
          - Preferred over structural grafts for ventral reconstruction
      • PEEK (Polyethyl Ether Ketone)
        • Characteristics:
          - Also preferred for ventral reconstruction
          - Favorable results in spondylodiscitis
          - High rates of subsidence and graft failure less likely than with structural grafts
      • CFRP (Carbon Fiber-Reinforced Polyether Ether Ketone)
        • Advantages:
          - Recently shown equivalent results to titanium
          - Minimize artifacts that interfere with postoperative imaging
          - Useful for postoperative CT and MRI assessment
        • Cautions:
          - Prospective study of 23 patients found markedly increased rate of screw loosening in CFRP screws compared with titanium
          - Advise caution against using CFRP screws in pyogenic spondylodiscitis
    • Structural (bone) grafts
      • Autograft
      • Allograft
  • Anterior Reconstruction options
    • Cervical
      • Most commonly used for anterior cervical reconstruction:
        • Static mesh and expandable cages
        • Anterior cervical plates
    • Thoracic and Lumbar
      • Used through both anterior and posterior approaches:
        • Static and expandable mesh cages
        • Static and expandable transforaminal lumbar interbody fusion cages
        • Bone grafts

Adjuncts

  • Bone Morphogenetic Protein-2 (BMP-2): Used safely in spondylodiscitis without additional complications

Wound Closure

  • General
    • The healing capacity in these patients is often compromised, and therefore, wound closure can prove challenging.
    • These patients should be considered as high risk for surgical site complications, and every effort should be made to prevent them.
  • Closure Technique
    • Local antibiotic use:
      • Thorough irrigation
      • Local use of antibiotics should be considered
      • Vancomycin locally in patients with gram-positive or unknown infections
      • Tobramycin in patients with gram-negative infections
    • Alternative local antibiotic delivery:
      • Biodegradable antibiotic-impregnated calcium sulfate beads for delayed elution of local antibiotics
    • Layered closure:
      • Layered closure over suction drains to obliterate dead space as much as possible
      • Vertical mattress nylon 3-0 sutures for skin
  • Incisional Vacuum-Assisted Closure (iVAC) Therapy
    • Indication:
      • Severe infections:
        • Initial débridement with deep VAC
          • Followed by relook débridement and closure 2-3 days later
      • Complex Cases
      • Unhealthy tissues:
        • In challenging cases, recommend consulting plastic surgery and plan for:
          • Primary flap closure
          • VAC therapy with secondary closure
    • Evidence: iVAC can markedly reduce the risk of surgical site complications after spine surgery, especially in high-risk patients

Differential Diagnosis

Tumor vs Infection

  • Tumor characteristics:
    - Does not destroy disc space (with rare exceptions: some vertebral plasmacytomas, reported metastatic cervical carcinoma)
    - Metastatic tumor involvement usually produces widespread bony involvement; less likely with single bone involvement
  • Infection characteristics:
    - Destroys disc space (key distinguishing feature)
    - Frequently involves adjacent two vertebrae

Tuberculous vs Pyogenic

  • Unlike pyogenic infections, the disc may be relatively resistant to tuberculous involvement in Pott’s disease