High Risk/Low Prevalence: Spinal Epidural Abscess

Spinal epidural abscess is rare, increasingly encountered, and easy to miss until permanent neurologic injury has occurred. The diagnosis hinges on pretest probability from back-pain risk factors and exam, then selective use of inflammatory markers to decide who needs whole-spine MRI with contrast.

Recognizing Spinal Epidural Abscess

• Rising but missed diagnosis: SEA incidence is increasing, yet 75-90% of cases are initially misdiagnosed and the median patient has 2 ED visits before diagnosis, a delay tightly linked to residual neurologic deficit.
• High-stakes neurologic harm: The morbidity is severe: irreversible paraplegia occurs in 4-22% of cases, fewer than half return to baseline neurologic function, and mortality still ranges from 2-20%.
• Typical spread patterns: SEA usually arises from hematogenous spread, contiguous infection, or direct inoculation, with Staphylococcus aureus causing 60-90% of cases and posterior thoracic involvement especially common.
• Classic triad limitation: Fever, back pain, and neurologic deficit occur together in under 8% of patients, so the classic triad is highly specific when present but far too insensitive to rule out disease.
• Risk factor framing: IV drug use and diabetes are major clues, but up to half of patients have no identified source, so a rough pretest probability has to integrate history, exam, and neurologic findings. We get into that bedside framing in the episode.

Diagnostic Workup and Imaging Strategy

• Inflammatory marker triage: ESR and CRP help sort higher-risk back-pain patients, with ESR above 20 mm/h present in about 95% of cases while a normal white count does not exclude SEA.
• MRI as gold standard: Whole-spine MRI with and without gadolinium is the diagnostic study of choice, with sensitivity and specificity above 90% and the added advantage of finding noncontiguous skip lesions.
• Skip lesion warning: Noncontiguous abscesses occur in roughly 15% of cases, which is why focused MRI can miss disease that extends across multiple vertebral levels.
• Alternative imaging caution: CT with IV contrast is less sensitive than MRI and may miss early infection, while CT myelogram is invasive and risks contaminating the subarachnoid space.
• Decision tool option: The SIRCH score combines 4 clinical variables to inform MRI decisions and, at the studied threshold, achieved very high sensitivity while reducing unnecessary scans. We walk through where it fits in the chapter.
• Lumbar puncture pitfall: LP is not recommended when SEA is on the differential because dural puncture may spread infection into the subarachnoid space.

Emergency Treatment Priorities

• Early specialist involvement: Source control matters early, so infectious disease and spine surgery consultation should happen up front when SEA is suspected or confirmed.
• Antibiotic timing nuance: Patients with septic shock or neurologic symptoms should receive antibiotics as soon as possible, while stable non-toxic patients can wait until after blood cultures are obtained.
• Empiric coverage targets: Initial therapy should cover MRSA, streptococci, and gram-negative bacilli; vancomycin plus ceftriaxone is a common starting regimen, with antipseudomonal escalation in the right host.
• Surgery usually required: Most patients ultimately need surgery, and decompression within 24 hours is associated with the best outcomes, especially with worsening deficits or hemodynamic instability.
• Medical management exceptions: A minority of patients can be managed with antibiotics alone, but failures occur in about 17% and there are important neurologic and microbiologic caveats we cover in the episode.

References:

1. Long B, et al. High risk and low prevalence diseases: Spinal epidural abscess. Am J Emerg Med. 2022 Mar;53:168-172. PMID: 35063888.
2. Davis DP, et al. Prospective evaluation of a clinical decision guideline to diagnose spinal epidural abscess in patients who present to the emergency department with spine pain. J Neurosurg Spine. 2011 Jun;14(6):765-70. PMID: 21417700.
3. Shroyer SR, et al. A Clinical Prediction Tool for MRI in Emergency Department Patients with Spinal Infection. West J Emerg Med. 2021 Aug 30;22(5):1156-1166. PMID: 34546893.