Vertebral osteomyelitis (VO)

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Spinal infection

General

• Often associated with discitis,
• Spondylodiscitis = Discitis + vertebral osteomyelitis

• VO has features similar to spinal epidural abscess (SEA)

Complications following VO

• Spinal epidural abscess

• Subdural abscess

• Meningitis

• Bony instability

• Progressive neurologic impairment
• Vertebral body collapse → kyphotic deformity
• Retropulsion of necrotic bone and disc fragments → compress spinal cord or CE

• Unique to cervical spine involvement: pharyngeal abscess

• Unique to thoracic spine involvement: mediastinitis

Epidemiology

• Vertebral osteomyelitis (VO) comprises 2–4% of all cases of osteomyelitis.

• Incidence
• 1:250,000 in general population.
• On the rise
• Incidence increases with age; most patients are > 50 years old.

• Male : female ratio is 2:1.

• Mortality 2-20%

Level (most to least common)

• Lumbar spine
• Is the most common site,

• Thoracic
• Thoracic VO may → empyema

• Cervical

• Sacrum

Risk factors

• IV drug abuse

• Diabetes mellitus
• Susceptible to unusual bacterial infections and even fungal osteomyelitis

• Hemodialysis
• A diagnostic challenge since radiographic changes of osteomyelitis can occur even in the absence of infection; see Destructive lesions of the spine

• Immunosuppression
• AIDS
• Chronic corticosteroid use
• Ethanol abuse

• Infectious endocarditis

• Following spinal surgery or invasive diagnostic or therapeutic procedures

• May occur in elderly patients with no other identifiable risk factors

Clinical

• Signs & symptoms
• Localized pain (90%),
• Fever (52%, with fever spikes and chills being rare),
• Weight loss,
• Paraspinal muscle spasm,
• Radicular symptoms (50–93%) or myelopathy.
• VO sometimes produces few systemic effects (e.g. WBC and/or ESR may be normal). ≈ 17% of patients with VO have neurologic symptoms.

• The risk of paralysis may be higher in the older patient, in cervical VO (vs. thoracic or lumbar), in those with DM or rheumatoid arthritis, and in those with VO due to S. aureus.

• Neurologic findings are uncommon initially, which may delay the diagnosis. Sensory involvement is less common than motor and long-tract signs because compression is primarily anterior.

Pathogenesis

• Source of infection
• UTI (the most common),
• Respiratory tract
• Soft-tissues (e.g. skin boils, IV drug abuse…)
• Dental flora.
• Unknown (not identified) 37% of cases

• Potential routes of spread
• Hematogenous
• Involves bone initially, and once infection is established in the subchondral space, spread is to the adjacent disc and thence to the next VB
• Arterial
• Venous: via spinal epidural venous plexus (Batson’s plexus)
• Direct extension
• Following surgery/LP,
• Trauma,
• Local infection

• Infection in the cartilaginous endplate

Organisms

• Staphylococcus aureus
• Most common pathogen (> 50%) as in SEA

• E. coli is a distant second

• Organisms associated with some primary infection sites
• IV drug abusers
• Pseudomonas aeruginosa
• S. aureus
• Urinary tract infections
• E. Coli
• Proteus spp.
• Respiratory tract infections
• Streptococcus pneumoniae
• Alcohol abuse
• Klebsiella pneumoniae
• Endocarditis
• Acute endocarditis: Staph. aureus
• Subacute endocarditis: Streptococcus spp.
• Tuberculous VO: Mycobacterium tuberculosis
• AKA tuberculous spondylitis, Pott’s disease.
• 1% of Total TB cases
• Has a predilection for the vertebral body, sparing the posterior elements.
• Starts from bone first - mimic tumour
• More common in third world countries.
• Typically symptomatic for many months.
• Usually affects more than one level.
• Most common Lower thoracic and upper lumbar
• Psoas abscess is common
• Sclerosis of the involved vertebral body may occur
• Definitive diagnosis
• Requires the identification of acid-fast bacilli on culture or Gram stain of biopsy material (may be done percutaneously).
• Neurologic deficit develops in 10–47% of patients,
• May be due to medullary and radicular artery inflammation in most cases.
• The infection itself rarely extends into the spinal canal
• However, epidural granulation tissue or fibrosis or a kyphotic bony deformity may cause cord compression.
• Treatment
• The role of surgical debridement and fusion with TB is controversial,
• Good results may be obtained with either medical treatment or surgery.
• Surgery indicated
• Definite cord compression is documented or
• Presence of complications such as abscess or sinus formation or spinal instability.
• Operate even neurology is bad for long time
• Slower course/ presentation - night sweats/ weight loss
• Consider patient age/ ethnicity/ other clinical symptoms
• Thoracic location
• Skip lesions
• Large paravertebral collections
• Relative disc sparing early on
• TB work up - CT CAP – usually pulmonary origin
• Indication for spinal biopsy? Target other areas first?
• Medical management – 6–12 months
• RIPE (Rifampin + Isoniazid + Pyrazinamide ± Ethambutol)
• Indication for surgery?
• 30 kyphosis at presentation
• 60 kyphosis at any point
• Progressive deficit
• Pain
• Refractory to medical management
• Large abscess


• Unusual organisms include
• Nocardia
• Mycobacterium avium complex (M. Avium and M. intracellulare) (MAC)
• Non-immunocompromised
• Usually elderly or on chronic steroids
• Pulmonary disease
• Immunocompromise (HIV)
• Cause VO similar to TB as part of disseminated disease.
• Polymicrobial infections: (10% of pyogenic VO infections)

Diagnostic tests

• Laboratories
• WBC: elevated in only ≈ 35% (rarely > 12,000), associated with poor prognosis.
• ESR: elevated in almost all. Usually >40mm/hr.
• Mean: 85. CRP: may be more sensitive than ESR, and may tend to normalize more quickly with appropriate treatment.
• See also normal values.

• 16s PCR
• PCR of microRNA to check for viable and non-viable bacteria

• 18s PCR
• PCR of mRNA for fungal infection

• Cultures/biopsy Culture
• Blood (positive in ≈ 50%), urine and any focal suppurative process.

• Needle biopsy with cultures
• Can usually be done percutaneously via transpedicular approach with CT or fluoroscopic guidance.
• May be helpful even if blood cultures are positive (different organisms retrieved in 15%) ∴ an attempt at direct culture from the involved site should be made. Ideally, cultures should be done before antibiotics are started.
• The yield of needle biopsy cultures ranges from 60–90%.
• Open biopsy is more sensitive, but morbidity is higher.

• Don’t forget to send for Histology
• Tumour
• TB

Imaging

• A comparison of sensitivities and specificities of various imaging modalities for vertebral osteomyelitis

Modality	Sensitivity	Specificity	Accuracy
Plain X-rays	82%	57%	73%
Bone scan	90%	78%	86%
Gallium scan	92%	100%	93%
Bone scan + gallium scan	90%	100%	94%
MRI	96%	92%	94%

• MRI
• T1WI → confluent low signal in vertebral bodies and intervertebral disc space.
• T2WI → increased intensity of involved VBs and disc space.
• Contrast: enhancement of VB and disc, also look for paraspinal and epidural mass.
• Differentiating TB vs pyogenic spondylodiscitis (Naselli 2021)
• TB cases were much more likely to affect >2 levels and non-contiguous
• T1
• Vertebral body
• TB is more likely to have heterogenous vertebral signal
• Pyogenic cases were hypointense in 98.8% (and hyperintense on T2)
• Disc
• TB more likely to have iso- or hyperintense discs
• Destruction
• TB: vertebral destruction
• Pyogenic: disc destruction.

• CT scan
• CT may be negative
• If done too early in the course.
• Look for
• Bony involvement
• Surgery planning bony anatomy

• Plain X-ray
• Changes take from 2–8 weeks from the onset of infection to develop.
• Earliest changes are loss of cortical endplate margins and loss of disc space height.

• Bone scan
• Three phase bone scan has reasonably good sensitivity and specificity.

• PET CT
• 90% sensitive/specific
• Patients who can't have MRI

• SPECT
• Technetium 99
• Low anatomic information, false −ves/+ves
• Indium-111 labelled WBC scan
• Gallium-67 scintigraphy

Work-up

• Clinical
• History of IV drug abuse, DM, immunocompromise, skin boil

• Physical exam: R/O radiculopathy & myelopathy, point tenderness over spine

• Diagnostic tests
• Bloodwork: WBC, ESR & CRP (a normal ESR is almost incompatible with VO), blood cultures
• Imaging
• MRI without and with contrast
• CT-myelogram
• If MRI is contraindicated
• Assesses bony anatomy and can demonstrate spinal canal compromise. Bone scan may occasionally be helpful if the diagnosis is still uncertain when suspicion is high
• Percutaneous needle biopsy with cultures
• CT guided under local
• Yield 48%
• Open biopsy (GA)
• Yield 76%
• 32% if antibiotics already started
• McNamara et al AJNR 2017
• Cultures should include: fungal, aerobic and anaerobic bacterial, and TB
• Blood culture 3x
• Yield 30-60%
• 20mls of blood in each samples

Treatment

Non-surgical treatment

• 90% of cases can be managed non-surgically

• Indication for non-surgical treatment
• Organism identified
• Antibiotic sensitivity
• Single disc space involvement with little VB involvement
• Minimal or no neurologic deficit
• Minimal or no spinal instability

• In cases with high suspicion for VO, antibiotics may be started as soon as biopsy has been performed (some treat even earlier).

• For details of antimicrobials, see spinal epidural abscess.

• Antibiotics
• IV antibiotics for at least 6 weeks (the rate of treatment failure is increased when IV antibiotics are given for < 4 weeks; longer, e.g. 12 weeks, if ESR not normalizing or if extensive bone involvement and paravertebral infection)
• Followed by 6–8 weeks of oral agents

• Pain medication as appropriate for pain

• TLSO brace
• To reduce pain (due to movement at involved site) and to reduce stress on weakened bone until healing
• Check upright films in the TLSO to verify stability in the brace
• Follow-up at approximately 8 and 12 weeks with X-rays in brace, then consider discontinuing brace if infection and pain are under control

Monitoring improvement

• Improvement on imaging can lag behind clinical response and ESR/CRP.

Surgical treatment

• Indications for neurosurgical intervention
• Biopsy for microbiology diagnosis
• Progression of disease despite adequate best-case antibiotic therapy
• Chronic infection refractory to medical management
• Spinal instability
• Spinal epidural abscess

• Options
Ant + post approaches
• Most cases as the infection is anterior
• The surgical approach generally should include anterior debridement and grafting followed by a staged or simultaneous posterior spinal stabilization procedure.
• Surgery should achieve complete debridement of nonviable and infected tissue, decompression of neural elements, and long-term stability through fusion (use of autogenous graft material is gold standard).
• Use of instrumented fusion is not contraindicated even for pyogenic infections.
• Use of titanium alloys is preferable to stainless steel due to increased bacterial adherence to stainless steel implants. In this setting
• Good evidence if stabilize bone can improve supply to fracture which can reduce infection load.
Posterior approaches only
• Indication
• Posterior epidural abscesses,
• Disc space infections below the conus with satisfactory anterior column support,
• Absence of significant paravertebral abscess.
Laminectomy alone
• No adequate
• Is associated with
• Deformity progression
• Instability
• Neurologic deterioration

• Although not routinely used, bone morphogenic protein (rhBMP-2) in 14 patients undergoing circumferential fusion for refractory infections did not produce complications.

Outcome

• The most consistent predictors of success for nonoperative treatment include
• Patients younger than 60 years
• Patients who are immunocompetent
• Infections with Staphylococcus aureus
• Decreasing ESR and CRP with treatment.

Differential diagnosis (Destructive lesions of the spine)

• Neoplastic: spine & spinal cord tumors
• Metastatic tumors with a predilection for bone: (Rare: Spinal epidural metastases)
• Prostate,
• Breast
• Renal cell
• Lymphoma
• Thyroid
• Lung
• Primary bone tumors
• Chordomas
• Osteoid osteoma
• Hemangioma

• Infection
• Vertebral osteomyelitis
• Occurs mostly in IV drug abusers, patients with diabetes mellitus, and hemodialysis patients.
• May have associated spinal epidural abscess.
• Discitis

• Chronic renal failure
• Some patients develop a destructive spondyloarthropathy that resembles infection

• Ankylosing spondylitis
• Bamboo spine (square VBs with bridging syndesmophytes)

• Lesions producing posterior scalloping of VB (mnemonic: AMEN)
• Acromegaly or achondroplasia
• Marfan syndrome or mucopolysaccharidosis
• Ehlers-Danlos
• Neurofibromatosis also: dural ectasia

• Lesions producing anterior scalloping of VB
• Aortic aneurysm
• Lymphoma
• Spinal TB

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