Spinal Epidural Abscess

A spinal epidural abscess (see image below) is a loculated purulent collection that may cause spinal cord injury via compression or vascular compromise (thrombophlebitis). If left untreated, an expanding suppurative infection in the spinal epidural space can impinge upon the spinal cord, producing sensory symptoms, weakness/motor dysfunction, and, ultimately, paralysis and even death. Frequently, diagnosis is delayed because the initial presentation are non-specific (ie, only nonspecific back pain without any "red flag" symptoms). Half of all cases of spinal epidural abscess are estimated to be misdiagnosed or have a delayed diagnosis.[1]  Early identification and timely surgical intervention may result in improved outcomes and preservation of neurological function. 

An MRI of the lumbar spine (T1-weighted, post-contrast) shows a spinal epidural abscess at the level of L3-L4, with an associated left paraspinal muscle abscess.

Risk factors for epidural spinal abscesses include intravenous drug use and immunosuppression from a variety of sources including HIV/AIDS and chronic steroid use as well as poorly controlled diabetes. Most commonly, hematogenous spread with seeding of the epidural space with bacteria is the most common mechanism via which spinal epidural abscesses form. Reported sources of infection are numerous and include bacterial endocarditis, infected indwelling catheters, urinary tract infection, peritoneal and retroperitoneal infections, and others. However, direct extension from nearby anatomic structures such as the vertebral bodies, intervertebral disk spaces, or psoas muscles can also give rise to an infection within the epidural space. In rare instances, infections can occur as a result of direct inoculation (eg, epidural steroid injections). 

The anatomy of the spinal epidural space makes it conducive to harboring infections. Posteriorly, the epidural space contains fat, small arteries, and a rich venous plexus. Anteriorly, the epidural space is a potential space with the dura tightly adherent to the vertebral bodies and ligaments. As such, abscesses occur more frequently in the larger, more densely vascular posterior epidural space. Some series suggest that dorsal spinal epidural abscesses are much more likely to present with weakness and severe neurologic deficit than ventral spinal epidural abscesses.[2]

The more clinically significant effects of the epidural abscess may be from involvement of the vascular supply to the spinal cord and subsequent venous infarction rather than direct compression. The development of symptoms is the result of meningeal irritation from the infection, structural instability from local tissue and ligamentous destruction, and neurological symptoms arising as a consequence of spinal cord compression and hypoxia from vascular compromise due to thrombophlebitis.

The incidence of spinal epidural abscess presenting to large tertiary care centers is estimated to be about 0.2-2.8 cases per 10,000 admissions. However, the incidence is suspected to be increasing in relation to an escalating rates of intravenous drug abuse (IVDU), with reported incidences as high as 5.1 cases per 10,000 admissions.[3]  Although there is a reported male predominance, and higher prevalence in the fifth to seventh decade of life, a wide range of demographic distribution amongst all ages is seen, concordant with patients' risk factors.[4] Cervical spine epidural abscesses are less common than those found in the thoracic and lumbar spine, although the former is associated with a higher risk of morbidity and mortality.[5]

Staphylococcus aureus is the most commonly reported pathogen,[6]  though many other bacteria have been implicated, including Staphylococcus and Pseudomonas species, Escherichia coli, Brucella, and Mycobacterium tuberculosis. Methicillin-resistant S. aureus (MRSA) is increasingly reported, particularly in patients with a history of MRSA abscesses, spinal surgery, or implanted devices.[7]  Immunosuppressed patients may have infections from unusual bacterial or fungal organisms.

Prognosis in general is related to the duration of spinal cord dysfunction and the degree of cord impairment at the time of diagnosis. Patients who present with neurological deficits are more likely to have a prolonged hospital and rehabilitation course compared to those who present neurologically intact. Cervical and thoracic abscesses appear to carry an increased risk of worse morbidity and overall functional recovery when compared with lumbar abscesses.

For patient education resources, see the Infections Center and Brain and Nervous System Center.

Clinical presentation of spinal epidural abscess may be quite variable. A complete clinical triad of fever, back pain, and neurologic deficit is not present in most patients.[6, 8] Early presentations may be subtle, and atypical presentations are not unusual. A 4-phase sequential evolution of spinal epidural abscess has been described, with (1) localized back pain, (2) radicular pain and paresthesias, (3) muscular weakness, sensory loss, and/or sphincter dysfunction, and, finally, (4) paralysis.[1]

The virulence of the infecting organism and the mode of infection contribute to the tempo of this progression. Abscesses from hematogenous spread tend to progress rapidly, while abscesses from osteomyelitis or discitis may evolve over weeks or months with slow progression of symptoms.

An evident source of infection in skin or soft tissue may be found. As such, in patients with clinical suspicion, blood work, blood cultures, urine cultures, and ESR/CRP should be obtained early during workup to help obtain an accurate diagnosis, which may prompt further imaging studies.

IV drug users are a high-risk group. Occurrences have been cited even in patients with a remote history of IV drug abuse.[3]

Symptoms may include the following:

• Fever is present in only about one third of patients
• Localized, severe back pain is often the first symptom in patients presenting with spinal epidural abscess
• Radiculopathy with radiating or lancinating pain, including chest or abdominal pain (at times this may simulate myocardial infarction or other causes of chest or abdominal pain)
• Spinal cord syndromes, typically involving paraparesis with prospective progression to paraplegia (epidural abscesses at the level of the cauda equina cause symptoms consistent with cauda equina syndrome rather than a spinal cord syndrome) ^[9]
• Headache and neck pain (nuchal rigidity) may be present, especially with cervical epidural abscesses

In patients with suspected spinal epidural abscess, a thorough neurological exam is beneficial to evaluate for any deficits.

• Palpation of the spine should be performed to elicit any worsening pain, which also helps localize the level(s) of the suspected epidural abscess. 
• A motor exam of each muscle group tested in isolation should be performed to evaluate for any focal weakness, or to elicit any asymmetry between contralateral sides.
• A sensory exam of cutaneous dermatomes (fine touch and pinprick sensation) should be evaluated.
• In patients with suspected cauda equina syndrome, a rectal examination should be performed, including testing for the preservation of pinprick sensation around the perianal area. A post-void residual can be obtained to evaluate for diminished bladder function.
• Testing for upper motor neuron signs, such as clonus, Babinski's, Hoffman's and hyper-reflexia should be tested. These can signify spinal cord compromise as a result of either a compressive lesion or vascular compromise. 

There is limited data available regarding the rate of complications among patients with spinal epidural abscesses. Often, neurological compromise occurs because of delay in diagnosis. Studies have reported a 30-50% failure rate for spinal epidural abscesses managed non-operatively.[10]  There are five main criteria that signify failure of medical management, and warrant surgical intervention: (1) neurological compromise; (2) failure of antibiotic treatment; (3) intractable back pain; (4) progressive spinal deformity; and (5) failure of diagnosis.

The diagnosis of spinal epidural abscesses is difficult due to numerous issues, and a thorough history, physical examination, and lab work should be obtained in a timely fashion. According to one study of retrospective chart reviews of 250 randomly selected patients, 119 had a new diagnosis of spinal epidural abscess, 66 (55.5%) of which experienced diagnostic error. Red flags that were frequently not evaluated in error cases included unexplained fever, focal neurological deficits with progressive or disabling symptoms, and active infection.[12]

The following laboratory tests may be helpful in patients suspected of having an spinal epidural abscess:

• CBC count, blood cultures, urinalysis/urine culture, and pre-operative lab studies. Fever may be absent in patients; however, leukocytosis is present in about two thirds of patients. ^[1]
• Elevated erythrocyte sedimentation rate (ESR) and/or C-reactive protein are often elevated in patients presenting with spinal epidural abscess. ^[13]
• Leukocytosis and ESR elevation are nonspecific laboratory findings and are not always present. Neither the presence of these findings nor the degree of laboratory abnormality is specific for spinal epidural abscess. A treatment guideline incorporating ESR, C-reactive protein, and other risk factors has been proposed based on a small patient series. ^[14]

While suspicion for spinal epidural abscess is influenced by patient history, clinical exam and labs, a definitive diagnosis requires obtaining contrast-enhanced MRI, or a CT myleogram in patients who are unable to obtain an MRI. Patients who present with spinal epidural abscess often have non-contiguous lesions, which may not be symptomatic;[15] thus, consideration should be given to obtaining imaging of the spinal neuroaxis in patients with suspected or confirmed abscess.

Treatment most often consists of both medical[16] and surgical therapy.

• If the patient remains neurologically stable and has a mechanically stable spine, antibiotic treatment may be held until a biopsy sample is obtained via imminent surgical intervention. ^[17]
• Empiric antibiotic coverage should include anti-staphylococcal antibiotics. With the increasing incidence of methicillin-resistant staphylococcal infections, initial coverage that includes antibiotics effective against MRSA is recommended, which can be narrowed once a definitive organism is identified. If the infection follows a neurosurgical procedure, an anti-staphylococcal penicillin, a third-generation cephalosporin, and an aminoglycoside are prescribed in combination. Culture results guide definitive therapy.
• Antibiotic treatment with CT-guided aspiration of the epidural space is increasingly used in patients without neurologic deficits.
• For the rare case caused by a fungal organism, the recommended drug is voriconazole at a dose of 6 mg/kg of body weight twice daily. ^[18]
• No specific guidelines exist for children, but a case series showed benefit with medical therapy of most patients. ^[19]

Surgical intervention to evacuate the spinal epidural abscess is beneficial to achieve favorable outcomes. A surgical procedure serves to obtain tissue for biopsy and culture, and evacuates the loculated collection(s) such that antibiotic treatment is more efficacious. 

In patients with cervical and/or thoracic spinal epidural abscess, there is an increased risk of neurological decline from thrombophlebitis causing spinal cord edema and infarction. Surgical risk benefits should be weighed against potential adverse effects.  Patients with lumbar epidural abscesses in whom there is an alternative lesion that may be biopsied (adjacent osteomyelitis, discitis, or psoas abscess), or a systemic source of infection, may be initially treated with antibiotic therapy.[20, 21]

In patients undergoing medical management of spinal epidural abscess, increasing neurologic deficit, persistent severe pain, progressive kyphosis and/or spinal instability, and failure of antibiotic treatment are all potential indications for surgical intervention. 

Prompt consultation with a spine surgeon should be considered when spinal epidural abscess is identified.

Consultation with an infectious disease specialist may be helpful in the selection of an antibiotic treatment regimen and length of therapy. 

Surgical intervention that provides decompression of the neural elements, as well as providing diagnosis, is the definitive treatment for patients presenting with spinal epidural abscesses, and is associated with a low rate (0-2.5%) of necessitating repeat surgical intervention for treatment failure.[22]  In one series, 13% of patients undergoing laminectomy alone, without instrumented fusion, developed a progressive kyphotic deformity that warranted repeat surgery.[23]  Despite the presence of infection, the rate of pseudoarthrosis in patients who undergo spinal fusion for treatment of epidural abscess is low (2.5-7%).[7, 22]

Surgical treatment inherently confers risk of bleeding, infection, or development of neurological deficits such as weakness, numbness, paresthesia, and loss of bowel/bladder/sexual function. and, in patients with significant medical co-morbidities, may result in severe morbidity and/or mortality.

Patients who undergo surgical treatment for evacuation of spinal epidural abscess should be mobilized early with physical and occupational therapy to reduce their risk of venous thromboembolism.

Patients with persistent symptoms should undergo repeat imaging to identify adequate treatment of the spinal epidural abscess, and to evaluate for the formation of any new lesion(s). Routine follow-up with standing x-rays of the spine should be obtained in order to assess for any progressive kyphosis or other spinal instability that warrants further surgical treatment. 

Patients should have long-term follow-up with an infectious disease physician to ensure compliance of treatment and to evaluate overall length of antibiotic therapy. Follow-up with infectious disease also serves to detect any metabolic abnormalities (eg, renal failure) that may occur as a result of prolonged antibiotic treatment. 

Antibiotic treatment should be initiated as soon as the diagnosis is reasonably considered, and is most often used in conjunction with abscess aspiration or surgical therapy. The usual duration of antibiotic therapy is 3-4 weeks, but may be lengthened in the presence of osteomyelitis.

As mentioned, in select stable patients, antibiotic therapy may be briefly delayed until material is obtained for culture.

Class Summary

Because S aureus is a common pathogen, anti-staphylococcal drugs should be included in the treatment regimen. An anti-staphylococcal penicillin, a cephalosporin, or vancomycin may be used. Again, with the increasing incidence of methicillin-resistant staphylococcal infections, coverage that includes an antibiotic that is effective against MRSA is recommended, which can be narrowed once cultures and sensitivities have resulted. If the patient has undergone a neurosurgical procedure recently, the penicillin should be combined with a third-generation cephalosporin and an aminoglycoside. Gram-stain and culture results are used to guide therapy.

Ceftriaxone

Third-generation cephalosporin that has broad gram-negative spectrum, lower efficacy against gram-positive organisms, and higher efficacy against resistant organisms. By binding to penicillin-binding proteins, arrests bacterial cell wall synthesis and inhibits bacterial growth.

Nafcillin

Treats infections caused by penicillinase-producing staphylococci. Used to initiate therapy in any patient in whom penicillin G-resistant staphylococcal infection suspected. Should not be used for treatment of penicillin G-susceptible staphylococci.

Parenteral therapy used initially in severe infections. Very severe infections may require very high doses. As condition improves, parenteral therapy should be changed to oral therapy.

Because of occasional occurrence of thrombophlebitis associated with parenteral route, particularly in the elderly, parenteral route should be used only for short term (24-48 h) and changed to oral route, if clinically possible.

Cefazolin

First-generation semisynthetic cephalosporin, which by binding to penicillin-binding proteins arrests bacterial cell wall synthesis and inhibits bacterial growth. Active primarily against skin flora, including S aureus. Total daily dosage is same for both IV and IM routes.

Metronidazole (Flagyl)

Used in combination with other antibiotics in epidural abscess following neurosurgical procedures. Active against various anaerobic bacteria and protozoa. Appears to be absorbed into cells, and intermediate-metabolized compounds formed bind DNA and inhibit protein synthesis, causing cell death.

Gentamicin

Used in combination with other antibiotics for epidural abscess following neurosurgical procedures. Aminoglycoside antibiotic used for gram-negative bacterial coverage. Commonly used in combination with both an agent against gram-positive organisms and one that covers anaerobes. Dosing regimens are numerous and are adjusted based on CrCl and changes in volume of distribution. May be administered IV or IM.

Vancomycin

Often used when MRSA or other resistant organisms are suspected. Potent antibiotic directed against gram-positive organisms and active against enterococci species. Useful in the treatment of septicemia and skin structure infections. Indicated for patients who cannot receive or whose conditions have failed to respond to penicillins and cephalosporins, or those who have infections with resistant staphylococci. For abdominal penetrating injuries, it is combined with an agent active against enteric flora and/or anaerobes.

To avoid toxicity, current recommendation is to assay vancomycin trough levels after third dose drawn 0.5 h prior to next dosing. Use creatinine clearance to adjust dose in patients with renal impairment.

Used in conjunction with gentamicin for prophylaxis in penicillin-allergic patients undergoing gastrointestinal or genitourinary procedures.

Patients may require inpatient or outpatient physical therapy rehabilitation to recover from any neurological injury sustained from spinal epidural abscess, or for routine post-operative care after spine surgery.

Frequently, patients require a prolonged course of antibiotics, and, as such, may require home health infusion or nursing care services. 

If the patient has neurological deficit from spinal cord damage, nursing attention for skin care, catheter care, and physical therapy may be necessary. Patients may also require further inpatient monitoring for any new or progressive neurological injury.

In patients with suspected epidural spinal abscess, transfer to a higher level of care may be required to obtain imaging studies (eg, contrast-enhanced MRI or CT myelogram) and access to a spine surgeon for evacuation of abscess.