Epidural Abscesses

What is Epidural Abscesses

Epidural abscess is an uncommon cause of spine pain that, if undiagnosed, can result in paralysis and life-threatening complications. Epidural abscess can occur anywhere in the spine and intracranially. It can occur spontaneously via hematogenous seeding, most frequently as a result of urinary tract infections that spread to the spinal epidural space via Batson plexus. More commonly, epidural abscess occurs after instrumentation of the spine, including surgery and epidural nerve blocks. The literature suggests that the administration of steroids into the epidural space results in immunosuppression, with a resultant increase in the incidence of epidural abscess. Although theoretically plausible, the statistical evidence—given the thousands of epidural steroid injections performed around the United States on a daily basis—calls this belief into question.

A patient with epidural abscess initially presents with ill-defined pain in the segment of the spine affected (e.g., cervical, thoracic, or lumbar). This pain becomes more intense and localized as the abscess increases in size and compresses neural structures. Low-grade fever and vague constitutional symptoms, including malaise and anorexia, progress to frank sepsis with a high-grade fever, rigors, and chills.

At this point, the patient begins to experience sensory and motor deficits and bowel and bladder symptoms as the result of neural compromise. As the abscess continues to expand, compromise of the vascular supply to the affected spinal cord and nerve occurs with resultant ischemia and, if untreated, infarction and permanent neurological deficits.

Epidural abscesses are most often found in the thoracolumbar spine. Bacteria can travel hematogenously into the epidural space, by adjacent tissue or from contamination postspinal procedure. Risk factors include diabetes, HIV infection, trauma, alcoholism, IV drug abuse, tattooing, neighboring infection, or hemodialysis.

Staph aureus makes up 63% of all infections. Methicillin-resistant Staphylococcus aureus (MRSA) makes up roughly one-fourth of all Staph infections. Fever may or may not be present. Symptoms include severe, focal pain.

Based on the extent of compression along the nerves and spinal cord, nerve injury ranges from radicular pain to paralysis. WBC, ESR, CRP, and blood cultures can be drawn. MRI should be performed if there is clinical suspicion of abscess. CT with IV contrast may be an alternative image modality. Abscess fluid culture is recommended. Treatment includes direct incision and drainage as well as antibiotic therapy. Empiric antibiotics following collection of two sets of cultures should start once the suspicion of infection is made. Treatment lasts for 4 to 8 weeks. Repeat MRI should be performed between 4 and 6 weeks. Serial WBC, ESR, and CRP values should be performed.

What are the symptoms of epidural abscess

A patient with epidural abscess initially has ill-defined pain in the general area of the infection. At this point, mild pain may occur on range of motion of the affected segments. The neurological examination is within normal limits. A low-grade fever, night sweats, or both may be present. Theoretically, if the patient has received steroids, these constitutional symptoms may be attenuated or their onset may be delayed. As the abscess increases in size, the patient appears acutely ill, with fever, rigors, and chills.

The clinician may be able to identify neurological findings suggestive of spinal nerve root compression, spinal cord compression, or both. Subtle findings that point toward the development of myelopathy (e.g., Babinski sign, clonus, and decreased perineal sensation) may be overlooked if not carefully sought. As compression of the involved neural structures continues, the patient’s neurological status may deteriorate rapidly. If the diagnosis is not made, irreversible motor and sensory deficit occurs.

How is epidural abscess diagnosed?

Myelography is still considered the best test to ascertain compromise of the spinal cord and exiting nerve roots by an extrinsic mass such as an epidural abscess. In this era of readily available magnetic resonance imaging (MRI) and high-speed computed tomography (CT), it may be more prudent to perform this noninvasive testing first, rather than wait for a radiologist or spine surgeon to perform a myelogram.

MRI and CT are highly accurate in the diagnosis of epidural abscess and are probably more accurate than myelography in the diagnosis of intrinsic disease of the spinal cord and spinal tumor. All patients suspected to have epidural abscess should undergo laboratory testing consisting of complete blood cell count, erythrocyte sedimentation rate, and automated blood chemistries.

Blood and urine cultures should be performed immediately in all patients thought to have epidural abscess to allow immediate implementation of antibiotic therapy while the workup is in progress. Gram stains and cultures of the abscess material also should be performed, but antibiotic treatment should not be delayed waiting for this information.

Differential Diagnosis

The diagnosis of epidural abscess should be strongly considered in any patient with spine pain and fever, especially if the patient has undergone spinal instrumentation or epidural nerve blocks for either surgical anesthesia or pain control. Other pathological processes that must be considered in the differential diagnosis include intrinsic disease of the spinal cord, such as demyelinating disease and syringomyelia, and other processes that can result in compression of the spinal cord and exiting nerve roots, such as metastatic tumor, Paget disease, and neurofibromatosis. As a general rule, unless the patient has concomitant infection, these diseases are routinely associated with only back pain and not with fever.

Treatment

The rapid initiation of treatment of epidural abscess is mandatory if the patient is to avoid the sequelae of permanent neurological deficit or death. The treatment of epidural abscess has two goals: (1) treatment of the infection with antibiotics and (2) drainage of the abscess to relieve compression on neural structures. Because most epidural abscesses are caused by Staphylococcus aureus , antibiotics such as vancomycin that treat staphylococcal infection should be started immediately after blood and urine culture samples are taken. Antibiotic therapy can be tailored to the culture and sensitivity reports as they become available. As mentioned, antibiotic therapy should not be delayed while waiting for definitive diagnosis if epidural abscess is being considered as part of the differential diagnosis.

Antibiotics alone rarely treat an epidural abscess successfully unless the diagnosis is made very early in the course of the disease; drainage of the abscess is required to effect full recovery. Drainage of the epidural abscess is usually accomplished via decompression laminectomy and evacuation of the abscess. More recently, interventional radiologists have been successful in draining epidural abscesses percutaneously using drainage catheters placed with the use of CT or MRI guidance. Serial CT or MRI scans are useful in following the resolution of epidural abscess; scans should be repeated immediately at the first sign of negative change in the patient’s neurological status.

Complications

Failure to diagnose and treat epidural abscess rapidly and accurately can result in disaster for the clinician and patient alike. The insidious onset of neurological deficit associated with epidural abscess can lull the clinician into a sense of false security that can result in permanent neurological damage to the patient. If epidural abscess or other causes of spinal cord compression is suspected, the algorithm shown below should be followed.CLINICAL PEARLS

Delay in diagnosis puts the patient and clinician at tremendous risk for a poor outcome. The clinician should assume that all patients who present with fever and back pain have an epidural abscess until proved otherwise and should treat accordingly. Overreliance on a single negative or equivocal imaging test is a mistake. Serial CT or MRI scans are indicated should there be any deterioration in the patient’s neurological status.BOX 79.1Algorithm for Evaluation of Spinal Cord Compression Caused by Epidural Abscess

• Immediately obtain blood and urine samples for cultures.
• Immediately start high-dose antibiotics that cover Staphylococcus aureus.
• Immediately order the most readily available spinal imaging technique (computed tomography, magnetic resonance imaging, myelography) that can confirm the presence of spinal cord compression (e.g., abscess, tumor).
• Simultaneously obtain emergency consultation from a spine surgeon.
• Continuously and carefully monitor patient’s neurological status.
• If any of the measures listed here are unavailable, arrange emergency transfer of patient to tertiary care center by the most rapidly available transportation.
• Repeat imaging and obtain repeat surgical consultation if any deterioration occurs in the patient’s neurological status.