Spinal Infections

What are spinal infections?

Infections that may involve different anatomical structures of the spine and often extend between them.

Spinal infections are classified according to their primary site:

• Spondylitis / vertebral osteomyelitis: infection of the vertebral bone.
• Discitis: infection of the intervertebral disc.
• Epidural abscess: accumulation of pus in the epidural space, with risk of spinal cord/nerve root compression.
• Surgical site infection: infection involving a previous operative field or instrumentation.

If not treated promptly, these infections may spread from one structure to another, leading to abscess formation, vertebral collapse, kyphotic deformity, instability and/or neurological deficit.

How common are they & who is at higher risk?

They are relatively uncommon, but occur more frequently in individuals with impaired immunity or following systemic bloodstream infection.

Spinal infections account for a small proportion of bone and joint infections. Risk is increased in:

• Elderly patients and individuals with diabetes mellitus.
• Patients under immunosuppression (e.g. corticosteroids, biologic agents) or with immunodeficiency.
• Patients with renal failure (especially on hemodialysis).
• Individuals with sepsis, endocarditis or another active source of infection.
• History of intravenous drug use (IVDU).
• Patients after spinal surgery or invasive spinal procedures (especially in the presence of additional risk factors).

Anatomically, infections most commonly involve the lumbar spine, followed by the thoracic and then the cervical spine.

How do they occur (hematogenous, post-operative, contiguous spread)?

Microorganisms may reach the spine through the bloodstream, during surgery, or by direct extension from adjacent infected tissues.

The three main mechanisms are:

• Hematogenous spread (the most common): bacteria disseminate via the bloodstream to the vertebrae and may subsequently involve the adjacent intervertebral discs.
• Direct inoculation: during surgery or invasive procedures (e.g. discectomy, epidural injections, catheter placement).
• Contiguous spread from adjacent soft-tissue infections.

Common portals of entry or primary foci include: urinary tract infections, skin and soft-tissue infections, respiratory infections, or bacteremia from other causes.

Which microorganisms are most commonly responsible?

Identification of the causative organism is crucial, as it determines antibiotic choice and duration of therapy.

• Staphylococcus aureus: the most common pathogen.
• Escherichia coli: the most frequent Gram-negative organism, often associated with genitourinary or gastrointestinal sources.
• Pseudomonas aeruginosa: more common in patients with a history of intravenous drug use, together with S. aureus.
• Mycobacterium tuberculosis (tuberculous spondylitis): more frequent in regions with higher TB prevalence.

In special settings (immunosuppression), fungal infections or atypical mycobacteria may be involved; therefore, biopsy specimens should always be sent for aerobic, anaerobic, fungal and mycobacterial cultures.

What are the symptoms and what should I watch for?

Back pain is the most common symptom, but infections may be “cryptic” without high fever. Neurological manifestations require urgent intervention.

Common symptoms:

• Persistent pain in the back, thorax, or neck that often does not improve with rest or simple analgesics.
• Radicular pain (sciatica/brachialgia) due to nerve root irritation.
• Fever (not always present).
• Malaise, night sweats, weight loss (particularly in chronic infections).

Require urgent evaluation:

• Weakness in arms or legs, progressive numbness, difficulty walking.
• Disturbances of urination or bowel control.
• Suspicion of epidural abscess (severe pain + fever + neurological symptoms).
• Pain after recent surgery or invasive spinal procedure with neurological deterioration.

How is the diagnosis made (laboratory & imaging)?

Diagnosis requires a combination of clinical suspicion, laboratory testing and appropriate imaging, with MRI as the study of choice.

Laboratory tests

• CRP and ESR: inflammatory markers are typically elevated in the acute phase and are highly sensitive for infection.
• White blood cell count: may be elevated, but not always.
• Blood cultures: should be obtained before initiating antibiotic therapy.

CRP has practical advantages: it is a key marker for monitoring treatment response, as levels change rapidly after effective antibiotic therapy.

Imaging

• Contrast-enhanced MRI: the gold standard, with very high sensitivity and accuracy for osteomyelitis, discitis, abscesses, and inflammation of paraspinal/epidural spaces.
• CT: useful for assessing bony destruction, surgical planning, and guiding biopsy.
• Bone scintigraphy: an alternative when MRI is contraindicated.

Important: MRI is excellent for initial diagnosis, but not always ideal for monitoring treatment response, as imaging abnormalities may persist despite clinical and laboratory improvement.

What is the role of cultures and biopsy?

Targeted antibiotic therapy requires identification of the causative microorganism.

In practice:

• Blood cultures are obtained before starting antibiotics (ideally from different sites/times, particularly during fever).
• If blood cultures are negative and suspicion remains high, a CT-guided biopsy is recommended to obtain tissue from the infected disc/vertebra or abscess.
• Specimens are sent for aerobic, anaerobic, fungal, and mycobacterial cultures.

Identification of the pathogen enables appropriate antibiotic selection, avoids unnecessary broad-spectrum therapy, and ensures safer and more effective treatment.

What is an epidural abscess and why is it an emergency?

An epidural abscess is one of the most dangerous complications: it can compress the spinal cord and cause rapid neurological deterioration.

A spinal epidural abscess is a collection of pus in the epidural space. It may develop as a complication of spondylitis/discitis or be associated with bacteremia. On MRI it typically appears as a collection with characteristic peripheral contrast enhancement.

Why is it an emergency?

• It may cause rapid weakness, gait disturbance, and sensory deficits.
• Damage may result not only from mechanical compression but also from venous congestion and impaired spinal cord perfusion.
• In the cervical/thoracic spine, surgical drainage is often recommended, especially when neurological deterioration is imminent.

In selected patients (known pathogen, minimal or no neurological symptoms, significant comorbidities), conservative management may be attempted, but even then close monitoring is mandatory.

How are they treated conservatively (immobilization & antibiotics)?

Most patients respond to non-surgical treatment, particularly when there is no instability, compressive abscess, or neurological deficit.

Conservative treatment includes:

• Immobilization with a brace or short-term rest, depending on pain severity and imaging findings.
• Intravenous and/or oral antibiotic therapy for typically 6–12 weeks, targeted to the identified organism once cultures are available.
• Follow-up for clinical improvement, fever resolution, and decline in inflammatory markers—primarily CRP.

CRP is particularly useful for assessing response to treatment. ESR may remain elevated for a longer period even with effective antibiotic therapy.

Treatment failure is suspected when there is persistent symptoms and elevated CRP after a reasonable period (e.g. ~4 weeks), or when new neurological symptoms develop.

When is surgery required and what are the goals?

Surgery is indicated when the infection threatens spinal stability, causes neural compression, or fails to respond to antibiotic therapy.

Main indications for surgery:

• Neurological deficit (weakness, myelopathy, sensory deterioration).
• Epidural abscess with evidence of spinal cord or nerve root compression.
• Spinal instability or vertebral collapse with progressive deformity.
• Failure of conservative treatment or persistent/recurrent infection.
• Need for tissue diagnosis when the pathogen has not been identified and urgent intervention is required.
• Infection or loosening of spinal instrumentation in postoperative patients (selected cases).

Three main goals of surgical treatment:

1. Identify the causative organism (tissue sampling) and determine antibiotic sensitivity.
2. Perform debridement and removal of infected tissue to restore a sterile environment and facilitate healing.
3. Restore mechanical stability of the spine (decompression ± fusion/stabilization).

Infection often involves the anterior column (vertebral body/discs). In such cases, debridement and anterior column reconstruction (e.g. with autograft or titanium cage) may be required, and when instability is present, posterior stabilization is added.

Today, immediate stabilization is feasible even in the presence of active infection when necessary to treat instability and improve function—fusion is always performed under appropriate antibiotic coverage and meticulous surgical technique.

What should I expect during follow-up and recovery?

Treatment requires time and systematic follow-up. Most patients ultimately improve, but consistent therapy and regular reassessment are essential.

Follow-up is usually based on:

• Clinical status: pain reduction, improved mobility, resolution of fever.
• Inflammatory markers: primarily CRP (serial measurements), with ESR as adjunct.
• Neurological examination: stability or improvement of neurological symptoms.
• Imaging when new or worsening symptoms occur or when complications are suspected.

Possible long-term sequelae include residual pain, spinal stiffness or spontaneous fusion, and in more severe cases, residual neurological deficit. Early diagnosis and appropriate treatment significantly reduce these risks.