Spinal epidural abscess is a collection of pus located between the dura mater and the overlying bone of the vertebral column: the epidural space. The epidural space contains fat and vascular areolar tissue which offers little resistance to the longitudinal spread of a spinal epidural abscess (SEA). Thus, it is common for a SEA to extend above and below the point of origin for an average of four disk spaces. Trapped between the dura mater and the vertebral bone, an expanding SEA can damage the spinal cord either by directly compressing the cord or by compromising blood flow through the spinal arteries. In either case, necrosis of the spinal cord can occur in a matter of hours. Recent studies report the incidence rate of SEA ranges from 1.96 to 2.8 per 10,000 hospital admissions, and has a clear male predominance. Risk factors include work related back trauma, iatrogenic causes (surgery, epidural anesthesia, or lumbar puncture), diabetes, hemodialysis, or a source of bacteremia (decubitus or mucosal ulcers, endocarditis, or urinary tract infection). Early and effective treatment of SEA requires a rapid diagnosis, which in turn requires a high index of suspicion. Undiagnosed or inadequately treated SEA often becomes a neurological disaster resulting in permanent paralysis or death.
Although virtually any organism can cause SEA, Staphylococcus aureus causes 60-90% of all cases. Less common pathogens include M. tuberculosis, fungi, and even parasites.
The combination of back pain, fever, and local vertebral tenderness upon palpation or percussion of the spine strongly suggests a SEA. This triad constitutes adequate reason to obtain a Magnetic Resonance Imaging (MRI) scan and to request neurosurgical help in evaluating the patient. Approximately 66% of patients with SEA present within two weeks of the development of symptoms. Historically, SEA has been characterized by four clinical stages: Stage 1 - Spinal ache; Stage 2 - Root Pain; Stage 3 - Weakness; and Stage 4 - Paralysis. As damage to the spinal cord progresses, the patient may exhibit bowel and bladder dysfunction, weakness or paralysis of the extremities, and sensory deficits. However, neurologic deterioration is highly variable and may not progress from one stage to the next in an orderly manner. Because it is not uncommon for acute SEA to progress from Stages 1 or 2 to Stage 4 (paralysis) in a matter of hours, the utility of staging SEA is questionable.
Traditionally, SEA has been considered a neurosurgical emergency. Standard management of patients with non-tuberculous SEA (NT-SEA) is immediate surgical drainage and decompression followed by six or more weeks of antimicrobial therapy directed against the organism isolated at surgery. Because Staph. aureus is the predominant offending organism, early therapy should include nafcillin or vancomycin. Although small numbers of patients have been treated for NT-SEA without surgery, the majority of these patients were either non- surgical candidates for other reasons; had minimal or no neurologic findings; or had been paralyzed for more than 48 hours with virtually no chance of reversal. Presently, data is inadequate to support the use of medical therapy without concomitant surgical decompression and drainage for NT-SEA. The bias for publishing only successfully treated cases indicates the need for randomized, controlled studies before non-surgical treatment can be condoned. Often tuberculous SEA can be treated with medical therapy alone.