A spinal epidural abscess is an accumulation of pus in the epidural space that can mechanically compress the spinal cord. Diagnosis is by MRI or, if unavailable, myelography followed by CT. Treatment involves antibiotics and sometimes drainage of the abscess.
(See also Overview of Spinal Cord Disorders.)
Spinal epidural abscesses usually occur in the thoracic or lumbar regions. An underlying infection is often present; it may be remote (eg, endocarditis, furuncle, dental abscess) or contiguous (eg, vertebral osteomyelitis, pressure ulcer, retroperitoneal abscess). In about one third of cases, the cause cannot be determined. The most common causative organism is Staphylococcus aureus, followed by Escherichia coli and mixed anaerobes. Occasionally, the cause is a tuberculous abscess of the thoracic spine (Pott disease). Sometimes the cause is bacteremia due to medical instrumentation, a dental procedure, or injection drug use. Rarely, a similar abscess occurs in the subdural space.
Symptoms and Signs of Spinal Epidural Abscess
Symptoms of spinal epidural abscess begin with local or radicular back pain and percussion tenderness, which become severe; pain may be worsened by recumbency. Fever is common.
Spinal cord compression may develop; compression of lumbar spinal roots may cause cauda equina syndrome, with neurologic deficits resembling those of conus medullaris syndrome (eg, leg paresis, saddle anesthesia, bladder and bowel dysfunction). Deficits progress over hours to days.
Diagnosis of Spinal Epidural Abscess
MRI
Because rapid treatment is necessary to prevent or minimize neurologic deficits, clinicians should consider spinal epidural abscess if patients have significant atraumatic back pain, particularly when there is focal percussion tenderness over the spine, or if they have a fever or have had a recent infection or dental procedure. Characteristic neurologic deficits are more specific but may occur later, so delaying imaging until these neurologic deficits are present can make a poor outcome more likely.
Pearls & Pitfalls
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Diagnosis of spinal epidural abscess is by MRI. Myelography followed by CT may be used if MRI is not available. Clinicians should consider doing MRI immediately if patients have unexplained back pain, even without neurologic findings, particularly if they have focal percussion tenderness and risk factors (eg, IV drug use, recent infection or bacteremia). Samples from blood and infected areas are cultured.
The presence of an inflamed disk (discitis) can help distinguish an abscess from a metastatic tumor. Discitis typically precedes abscess formation, whereas a metastatic tumor does not affect the disk; it destroys nearby bone.
Lumbar puncture is contraindicated because it may trigger cord herniation if the abscess completely obstructs flow of cerebrospinal fluid (CSF).
Plain x-rays are not routinely indicated but show osteomyelitis in about one third of patients. Erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) is elevated, but this finding is nonspecific.
Treatment of Spinal Epidural Abscess
Antibiotics
If abscess causes neurologic compromise, immediate drainage
Antibiotics with or without parenteral needle aspiration may be sufficient treatment for a spinal epidural abscess; however, abscesses causing neurologic compromise (eg, paresis, bowel or bladder dysfunction) are surgically drained immediately. Pus is gram-stained and cultured.
Key Points
A spinal epidural abscess typically causes local or radicular back pain, percussion tenderness, and fever; if the abscess compresses the spinal cord, neurologic deficits (leg paresis, saddle anesthesia, bladder and bowel dysfunction) develop.
Because rapid treatment is necessary to prevent or minimize neurologic deficits, clinical suspicion of spinal epidural abscess should be high (eg, if patients have unexplained atraumatic back pain, particularly with focal percussion tenderness or risk factors); if it is suspected, MRI or, if unavailable, myelography followed by CT should be done immediately.
If an abscess is causing neurologic deficits, immediately drain the abscess surgically; treat all abscesses with antibiotics that cover staphylococcus, anaerobes, and sometimes gram-negative bacteria.
