Spinal Epidural Abscess

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Epidural abscess is a commonly missed rare infection of the central nervous system. Such abscesses are enclosed in restricted space which means that when they expand they can compress important neurological structures. This can lead to severe disability and even death.

Epidemiology

Spinal epidural abscess is rare. The median age is 50 years, with greatest prevalence between 50 and 70. The incidence may be higher in males.

Risk Factors

  • Immunocompromising conditions: diabetes, alcohol use disorder, chronic liver disease, HIV, CKD, HIV/AIDS
  • Spinal interventions: spinal surgery, epidural catheters., paraspinal injections of glucocorticoids or analgesics.
  • Other: Injection drug use, epidural anaesthesia, tattooing, acupuncture, contiguous bony (e.g. osteomyelitis) or soft tissue infection, trauma, dental abscess, infective endocarditis.

Pathology

  • S. aureus accounts - 63%
  • Gram-negative bacilli - 16%
  • Streptococci - 9%
  • Uncommon: anaerobes, mycobacteria, fungi, coagulase negative staphylococci (with spinal instrumentation), P. aeruginosa (IVDA).

Pathogenesis

Bacteria can spread haematogenously, from local tissues, or by direct inoculation. The most common sources are soft tissue infections and sequelae from spinal surgery or other invasive spinal procedures. The source is unknown in one third of cases.

Sources of infection for spinal epidural abscess
Source Percentage
No source found 30
Skin and soft tissue 22
Spinal surgery or procedures 12
Injection drug use 10
Other sources, including epidural catheters 8
Bone or joint 7
Urinary tract 3
Upper respiratory tract 3
Sepsis 2
Abdomen 2
Intravascular catheter associated <1
From Sources of infection for spinal epidural abscess. In: UpToDate.

Clinical features

The classic triad is fever, back pain, and neurologic deficits. However only a small percentage of affected individuals have all three of these features. Initial symptoms and signs are often nonspecific such as simply fever and malaise.

  • Back pain: This is the most common symptom, and pain can be present from 1 day to 2 months.
  • Fever: This is most likely to be absent
  • Neurological deficits: also commonly absent. Deficits can include motor weakness, radiculopathy, and bladder/bowel dysfunction. Neurologic deficits can occur with even small abscesses.

The typical sequence of events is as follows:

Prevalence of abnormal physical findings
Finding Prevalence
Fever (T>38°C) 19-32%
Focal spinal TTP 52-62%
Diffuse spinal TTP 63-65%
Positive SLR 11-13%
Abnormal sensation 17-27%
Weakness 29-40%
Abnormal reflexes 8-17%
Abnormal rectal tone 5-10%
Saddle anesthesia 2%

Diagnosis

There should be a a low threshold for suspicion in any patients with fever and back pain in the presence of risk factors. In this setting MRI with gadolinium should be arranged (90% sensitivity). Blood tests include FBC, CRP, ESR, and blood cultures. MRI with gadolinium

Unfortunately due to the nonspecific initial symptoms the diagnosis is usually delayed and patients will usually present to doctors multiple times before the diagnosis is made.

Staging is as follows:

  1. Back pain at affected site
  2. Nerve root pain from affected level
  3. Weakness, sensory deficit, bladder/bowel dysfunction
  4. Paralysis

Management

Patients are managed as an inpatient with urgent neurosurgical review. After diagnosis the causative organism is isolated from blood cultures and the abscess. Surgical intervention when done emergently may improve outcomes, but occasionally non-surgical treatment is suitable. Antibiotics are started as soon as possible. The duration of treatment is usually planned by infectious diseases and is typically several weeks.

Prognosis

Death: 5-7%

Irreversible paraplegia: 4-22%

References

D Sexton. Spinal epidural abscess In: UpToDate. May 2020. Accessed May 2022.