If an abscess is known to be present, lumbar puncture should not be performed, however, if the CSF space is inadvertently breached, the CSF usually contains white cells but of surprisingly small number (fewer than 100/mm3), both polymorphonuclear leukocytes and lymphocytes, unless of course, the needle penetrates the abscess, in which case pus is obtained. The CSF protein content is high, (100 to 400 mg/100 mL or more) but the glucose is normal. Elevation of the sedimentation rate, C-reactive protein, and peripheral neutrophilic leukocytosis are additional indicators to the diagnosis. The last of these tests is abnormal in two-thirds of cases. Blood cultures demonstrate the organism in a similar proportion. Cultures from the CSF are infrequently positive. The decades old series reported by Baker and colleagues is still a valuable reference, as is the more recent discussion by Darouiche. The differential diagnosis includes other forms of spinal cord compression and, in cases with areflexic spinal shock, tetraparesis and respiratory failure, Guillain-Barré syndrome.
Treatment The foregoing clinical findings and signs of am myelopathy call for MRI to be performed relatively quickly or CT myelography if MRI is not possible, to demonstrate the mass of the abscess and to determine its level as summarized by Ropper and Ropper. If not treated surgically by laminectomy and drainage before the onset of paralysis, the spinal cord lesion, which is probably partly a result of venous ischemia, becomes more or less irreversible. Broad-spectrum antibiotics in large doses must be given initially and the choice of treatment is then refined based on cultures from the abscess or the blood, or on a presumed source of bacteria, usually found to be staphylococcus.
When osteomyelitis of a vertebral body is the primary abnormality, the epidural extension may implicate only a few spinal sensory and motor roots, leaving long tracts and other intramedullary structures intact. In some cases with cervical epidural abscesses, stiff neck, fever, and deltoid-biceps weakness are the main neurologic abnormalities. Having emphasized the urgency of treatment, there are instances of small epidural abscesses that do not compress the cord and are limited to one or at most two levels for which we have avoided surgery by administering antibiotics alone. Also, lumbar epidural abscess and cauda equina compression without neurologic signs may be, in some cases, treated solely with antibiotics, although many surgeons favor drainage, which must be undertaken in any case, if osteomyelitis develops. Antibiotics are continued for several weeks, and the patient should be examined at regular intervals and have sequential MRI scans of the affected region.
Even after apparently successful drainage and antibiotic treatment of an epidural abscess, there may be a slowly progressive and then static syndrome of partial spinal cord compression. This is the result of formation of a fibrous and granulomatous reaction at the operative site. Distinguishing this sterile inflammatory mass from residual epidural abscess is quite difficult, even with enhanced MRI, but persistent fever, leukocytosis, and an elevated sedimentation rate, C-reactive and peripheral white blood cell count suggest that surgical drainage of the abscess was incomplete.
Spinal subdural abscess due to bacterial infections also occur and, clinically, are virtually indistinguishable from epidural ones on clinical grounds. The MRI will usually clarify the situation but a clue is provided by the CT myelogram, in which the subdural lesion has a less sharp margin and usually, a greater vertical extent. The epidural and subdural infections, if they smolder owing to delayed diagnosis or inadequate therapy, may also evolve into a local chronic adhesive meningomyelitis.
Subacute pyogenic infections and granulomatous infections (tuberculous, fungal) may also arise in the spinal epidural space, as noted further on.