Spinal Epidural Abscess
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.
| 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 with untreated abscesses: back pain (focal and severe) -> radicular pain -> motor weakness, sensory changes, bladder or bowel dysfunction -> paralysis (quickly irreversible)
| 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:
- Back pain at affected site
- Nerve root pain from affected level
- Weakness, sensory deficit, bladder/bowel dysfunction
- 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.
