Spinal infections

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Spinal infections, an umbrella term covering osteomyelitis, diskitis, and spinal epidural abscess, are a rare but serious cause of back pain. They are caused by bacteria (most commonly Staphylococcus aureus) introduced during surgery or via hematogenous or contiguous spread from other infections, which leads to inflammation and abscess formation. Risk factors include immunosuppression, bacteremia, and recent surgery. Patients typically present with nonspecific symptoms such as back pain and fever; however, the presentation depends on the location and extent of the infection and may include signs of cord compression. Diagnosis is often delayed due to the nonspecific nature of symptoms, as well as the overlap between symptoms of spinal infection and those of the underlying source of infection, e.g., skin and soft tissue infection or urinary tract infection. Diagnosis is based on blood cultures, inflammatory markers, and advanced imaging of the spine; the first-line imaging modality is MRI with and without contrast. If initial studies are negative, a CT-guided biopsy may be appropriate. Patients with hemodynamic instability or signs of neurologic compromise should be started on antibiotics immediately and urgently referred to a neurosurgeon. For stable patients, antibiotic therapy is typically deferred until the causative organism is known. Additional surgical management should be considered for patients with complications such as abscesses or spinal deformity, or who have ongoing severe pain or fail to respond to antibiotic therapy.

• Vertebral osteomyelitis (spondylitis): an infection of the vertebral body. Subtypes include:
  • Granulomatous vertebral osteomyelitis: most commonly caused by tuberculosis (Pott disease). Risk factors include immigration from countries with high TB prevalence and coinfection with HIV. ^[2]
  • Pyogenic vertebral osteomyelitis: most common form; typically occurs secondary to infection with Staphylococcus aureus
• Diskitis: an infection of the intervertebral disk space
• Spondylodiskitis: an infection of both the vertebral body and intervertebral disk space
• Spinal epidural abscess: a suppurative infection in the epidural space

• Incidence: ∼ 5.4 per 100,000 in 2013 ^[3]
• ♂ > ♀ ^[2]
• Mean age: 59–69 years ^[2]

Epidemiological data refers to the US, unless otherwise specified.

Routes of infection

• Spinal infection may arise from: ^[4][5]
  • Hematogenous spread from a distant focus (e.g., skin and soft tissue infection, urinary tract infection)
  • Direct inoculation (e.g., during spinal surgery or due to trauma)
  • Contiguous spread from adjacent infections (e.g., aorta, esophagus)
• Frequently, a primary source of infection cannot be identified. ^[5]

Pathogens ^[2][4][6]

• Common
  • Staphylococcus aureus (most common; , accounting for > 40% of cases) ^[2]
  • Escherichia coli (second most common)
  • Pseudomonas aeruginosa
  • Proteus mirabilis
  • Enterobacteriaceae
  • Beta-hemolytic streptococci
• In special patient groups
  • After spinal surgery, usually: ^[4]
    • Coagulase-negative staphylococci, e.g., Staphylococcus epidermidis
    • Propionibacterium acnes
  • In areas of high endemicity or in patients emigrating or traveling from those areas, also consider:
    • Mycobacterium tuberculosis: resulting in tuberculous spondylitis
    • Brucella spp.
  • In patients with immunosuppression, long-term indwelling venous catheters, or IV drug use, also consider fungal species.

Risk factors ^[2][6][7]

• Age > 50 years ^[5]
• Sickle cell disease ^[8]
• Immunocompromise: e.g., steroid use, HIV infection
• Intravenous drug use
• Recent bacteremia
• Infective endocarditis
• Recent spinal surgery and instrumentation
• Intravascular devices
• Malnutrition
• Chronic medical conditions:
  • Diabetes mellitus
  • Renal failure
  • Heart disease
  • Liver cirrhosis
• Malignancy

All types of spinal infections have similar clinical features. In cases of hematogenous spread, features of the primary infection (e.g., urinary tract infection, skin and soft tissue infection) may dominate the clinical presentation. ^[2][6]

• Back or neck pain ^[4][5][6]
  • Onset is typically insidious, worsening over several weeks to months.
  • Occurs in a localized area
  • Worse during physical activity and at night
  • May radiate to the abdomen, hip, leg, scrotum, groin, and/or perineum
  • Severe, sharp back pain may indicate an epidural abscess.
  • Examination findings
    • Pain is exacerbated by palpation or percussion of the area.
    • Palpation of paravertebral muscles can cause tenderness and spasm.
    • Spinal mobility is reduced.
    • Neurological signs and symptoms may be present: See “Complications.”
• Fever: present in up to 45% of patients. ^[6]

The diagnosis of spinal infection is often delayed because back pain is a common and nonspecific symptom, while spinal infections are rare.

Approach ^[6][9]

• Obtain the following tests in all patients with suspected spinal infections:
  • ESR and CRP
  • Two sets of bacterial blood cultures
  • MRI spine
• If all initial tests are negative but clinical suspicion remains high, consider:
  • Nuclear medicine scan
  • CT-guided aspiration biopsy
• Suspected hematogenous or contiguous spread: Identify and treat the underlying cause.

Back pain and fever can also occur in underlying causes such as pneumonia and pyelonephritis; screen patients with spinal infections carefully to avoid missing a concurrent infection.

Laboratory studies ^[6]

• ↑ CRP, ↑ ESR ^[6]
• CBC: typically elevated ^[6]
• Blood cultures: two sets, aerobic and anaerobic, from two separate peripheral venipuncture sites
• Additional testing when less common pathogens are suspected, e.g.:
  • Brucella: Blood cultures and serology
  • Fungal infections: fungal cultures, serology, and antigen detection assays
  • Tuberculosis: PPD, interferon γ release assay, or mycobacterial culture for Mycobacterium tuberculosis
• If initial testing shows no signs of infection, consider checking serum protein electrophoresis to evaluate for multiple myeloma.

Imaging studies ^[6][10]

Imaging findings may show osteomyelitis, diskitis, abscess formation, or a combination of the three.

MRI spine with and without IV gadolinium contrast ^{[5][6][11][12]}

• Indication: first-line imaging modality for suspected spinal infection (highest sensitivity) ^[6]
• Findings
  • Pyogenic vertebral osteomyelitis
    • Loss of vertebral endplate definition with change in signal intensity of disks and vertebral bodies (hypointense on T1 , hyperintense on T2)
    • Contrast enhancement of disks and vertebral bodies
    • Adjacent soft-tissue inflammation
  • Granulomatous vertebral osteomyelitis: See “Diagnostics” in “Pott disease.”
  • Spinal epidural abscess ^[2][13]
    • Early infection (phlegmon): homogeneous enhancement in epidural space
    • Established abscess: rim enhancement surrounding a nonenhancing center

Additional imaging studies

• CT spine with IV contrast ^[2][14]
  • Indications
    • Evaluation of calcifications or sequestra
    • Percutaneous needle biopsy
  • Findings ^[9]
    • Adjacent bone edema
    • Disk space narrowing
    • Vertebral endplate erosion
    • Sequestra formation
    • Calcifications
    • Spinal epidural abscess: rim enhancement after contrast administration
• Nuclear medicine scans: adjunct to MRI if initial MRI results are negative or equivocal
  • Modalities: A combination of scans may be used. ^[6]
    • 3-phase technetium-99m bone scan
    • Gallium scan
    • PET scan
  • Findings: increased activity in the infected area
• X-ray
  • Indications: not used to diagnose spinal infections but a potential initial study in a patient presenting with back pain
  • Findings ^[15][16]
    • Typically normal for the first 3–6 weeks of infection ^[6]
    • After 3–6 weeks:
      • Narrowing of disk space
      • Erosion of vertebral endplates
      • Periosteal thickening
      • Lytic lesions
      • New bone apposition
      • May show some paraspinal soft tissue changes

If imaging is inconclusive but suspicion for spinal infection persists, repeat after 1–3 weeks. ^[6]

CT-guided aspiration biopsy ^[6]

• Confirmatory test
  • A biopsy of the affected area is performed and material is sent for microbiologic and pathologic examination.
  • Indications to repeat the biopsy include:
    • Inadequate tissue drawn
    • Specimen growing a likely skin contaminant
    • Suspected organism is hard to culture (e.g., fungi, mycobacteria, or Brucella spp.).
• Indications
  • Patients with spinal infection in whom blood cultures or serology have not identified a causative organism
  • Consider for patients with suspected vertebral osteomyelitis and concurrent bloodstream infection

In patients with a nondiagnostic workup and negative CT-guided aspiration biopsy in whom the clinical suspicion of spinal infection remains high, a repeat biopsy (CT-guided or surgical) should be obtained. ^[6]

See “Differential diagnosis of acute back pain.”

The differential diagnoses listed here are not exhaustive.

The following recommendations pertain to the treatment of suspected pyogenic vertebral osteomyelitis and spinal epidural abscess. Involve specialists (infectious disease, neurosurgery) early. For treatment of tubercular vertebral osteomyelitis, see “Pott disease.”

Approach ^[6]

• Initial management: Assess the need for empiric antibiotic therapy and invasive treatment.
  • Initiate empiric antibiotic therapy and obtain cultures and an urgent neurosurgical consult if any of the following criteria are met:
    • Suspected spinal epidural abscess
    • New or progressive neurologic symptoms
    • Hemodynamic instability or impending sepsis
  • If none of the criteria are fulfilled, antibiotic therapy can be delayed until the causative organism is identified.
• Ongoing management
  • Initiate pain management
  • If mobility is limited, start preventative measures against decubitus ulcers.
  • Identify and treat underlying causes.
  • Regularly reassess for new neurologic signs and symptoms.
  • Tailor antibiotic therapy based on culture and susceptibility results.

Antimicrobial therapy ^[6]

Empiric antimicrobial therapy for spinal infections

• Indications
  • New or progressive neurologic symptoms
  • Hemodynamic instability
  • Sepsis
• Coverage: : must include Staphylococcus spp., including MRSA, Streptococcus spp., and gram-negative bacilli
• Recommended regimens
  • First line: vancomycin PLUS
    • A third-generation cephalosporin (e.g., ceftriaxone )
    • OR PLUS a fourth-generation cephalosporin (e.g., cefepime )
  • Alternative in case of allergy: daptomycin PLUS a fluoroquinolone, e.g., ciprofloxacin

Diagnostics aimed at identifying the causative pathogen (e.g., blood cultures or biopsy) should be performed at the same time that empiric antibiotics are started.

Tailored antimicrobial therapy

• Initiate IV antimicrobial treatment based on culture and susceptibility results.
• Consider switching to oral antibiotics if symptoms improve and inflammatory markers trend downward.

Spinal infections are usually treated with 6 weeks of antibiotics, but the duration may vary based on the causative organism and patient response to treatment. Consult an infectious disease specialist prior to stopping treatment.

Invasive treatment

CT-guided drainage and irrigation ^[17]

• Indication: epidural and paraspinal abscesses
• Contraindications: anterior abscess, spinal instability, associated osteomyelitis or spondylodiskitis

Surgery

• Indications ^[2][4][6]
  • Epidural abscesses and paraspinal abscesses, particularly those large in size (e.g., ≥ 2.5 cm) ^[2][4][18]
  • Spinal instability or deformity
  • New or progressive neurologic impairment
  • Intractable pain
  • Need for open biopsy ^[4]
  • Infections associated with spinal implants
  • Persistent or recurrent bloodstream infection
• Objectives ^[2][6]
  • Debridement of infected tissues, with removal of prosthetic material if necessary
  • Obtaining material for microbiologic/histologic evaluation
  • Decompression of neural structures
  • Spinal fixation
  • Abscess drainage

• Neurologic ^[4]
  • Motor weakness or paralysis ^[4]
  • Sensory loss
  • Meningitis ^[6]
• Infectious
  • Sepsis
  • Abscess in the surrounding soft tissues
    • Prevertebral abscess: may manifest with neck pain, difficulty swallowing, difficulty breathing, and potential respiratory failure (secondary to the abscess compressing the trachea and obstructing the airway)
    • Paravertebral abscess: Symptoms frequently overlap with those underlying spinal infection.
  • Psoas abscess
  • Infectious aortitis ^[19]

Severe complications can occur if the diagnosis or treatment of spinal infections is delayed.

We list the most important complications. The selection is not exhaustive.