eMedicine Specialties > Neurology > Neurological Infections

Spinal Epidural Abscess

Author: J Stephen Huff, MD, Associate Professor, Emergency Medicine and Neurology, Department of Emergency Medicine, University of Virginia Health Sciences Center
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Updated: Aug 13, 2009

Introduction

Background

A spinal epidural abscess threatens the spinal cord or cauda equina by compression and also by vascular compromise (see Media files 1-2). If untreated, an expanding suppurative infection in the spinal epidural space impinges on the spinal cord, producing sensory symptoms and signs, motor dysfunction, and, ultimately, paralysis and death. Intervention early in the course of the disease undoubtedly improves the outcome. Frequently, diagnosis is understandably delayed because the initial presentation may be only back pain. One half of cases are estimated to be misdiagnosed or have a delayed diagnosis.¹ At times, radicular symptoms may lead to a chief complaint of chest pain or abdominal pain² , mimicking a myocardial infarction or an acute abdomen.³

Pathophysiology

The spinal epidural space is not a uniform space. Posteriorly, the epidural space contains fat, small arteries, and the venous plexus. Infections in this space may spread over several vertebral levels. Anteriorly, the epidural space is a potential space with the dura tightly adherent to the vertebral bodies and ligaments. Abscesses occur more frequently in the larger posterior epidural space. Most spinal epidural abscesses occur in the thoracic area, which is anatomically the longest of the spinal regions.

Hematogenous spread with seeding of the epidural space is the suspected source of infection in most children and is thought to occur in many adults as well. Reported sources of infection are numerous and include bacterial endocarditis, infected indwelling catheters, urinary tract infection, peritoneal and retroperitoneal infections, and others.

Direct extension of infection from vertebral osteomyelitis occurs in adults and rarely in children.

Epidural catheters and injections may lead to direct innoculation of the epidural space. The source of infection is not identified in many patients.

The more clinically significant effects of the epidural abscess may be from involvement of the vascular supply to the spinal cord and subsequent infarction rather than direct compression. Staphylococcus aureus is the most commonly reported pathogen⁴ , though many other bacteria have been implicated, including Staphylococcus and Pseudomonas species, Escherichia coli, Brucella, and Mycobacterium tuberculosis. Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly reported particularly in patients with spinal surgery or implanted devices.

Frequency

United States

The frequency in large tertiary care centers is estimated to be about 2.8 cases per 10,000 admissions. The incidence is suspected to be increasing in relation to intravenous (IV) drug abuse.⁵

International

Because these abscesses occur rarely, the frequency is unknown. It probably parallels the US experience of rarity, although limited diagnostic capabilities in medically underserved countries might increase its importance as a health risk.

Mortality/Morbidity

If untreated, spinal epidural abscess causes progressive paraplegia and death.

Sex

Older studies found an equal sex ratio; more recent data indicate a male predominance, likely reflecting the pattern of IV drug use.

Age

The average age is older than 50 years, but spinal epidural abscess can occur at any age.

Clinical

History

Clinical presentation may be quite variable. The clinical triad of fever, back pain, and neurologic deficit is not present in most patients.^4,6 Early presentations may be subtle, and atypical presentations are not unusual. A 4-phase sequential evolution has been described, with (1) localized spinal pain, (2) radicular pain and paresthesias, (3) muscular weakness, sensory loss, and 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.
• Frequently the patient gives a history of back strain or mild injury.
• An evident source of infection in skin or soft tissue may be found.
• IV drug users are a high-risk group. Occurrences have been cited even in patients with a remote history of IV drug abuse.⁵
• Cases are frequently reported in patients with diabetes mellitus, which is a risk factor in 50% of reported patients; alcoholism; and conditions involving chronic immunosuppression.
• Hematogenous seeding of the epidural space with abscess formation may stem from intravenous lines, urinary catheters, or implantable devices. Direct inoculation of the epidural space may follow spinal surgery, epidural catheter placement, or epidural injections.
• Symptoms include the following:
  • Fever, present in only about one third of patients
  • Localized back pain in most patients, often the first symptom
  • Radiculopathy with radiating or lancinating pain, including truncal girdle pain (This, at times, 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.)
  • Central cord syndrome from epidural abscess has also been reported.⁷
  • Sphincter dysfunction, including incontinence or increased residual urine volumes
  • Headache and neck pain may be present, especially with cervical epidural abscesses. (Of course, these symptoms might also suggest meningitis.)

Physical

• Physical findings vary with the degree of spinal cord compression or dysfunction.
• In the most advanced cases, a transverse cord syndrome is seen with motor and sensory levels found with neurologic examination.
• Localized tenderness to percussion or palpation at the site of the abscess may be noted. Paraspinal muscle spasm may be present.
• Signs of spinal cord dysfunction may be observed.
  • Complete transverse spinal cord syndrome with paraplegia and sphincter dysfunction
  • Incomplete spinal cord syndromes
• Reflexes may vary from absent to hyperreflexia with clonus and extensor plantar (Babinski) responses. Areflexia may indicate spinal shock with transient inhibition of spinal reflexes.
• Nuchal rigidity may be present, particularly with cervical epidural abscesses.

Causes

• Most cases arise from hematogenous seeding of the epidural space from a distant source of infection.
• A few cases are the result of direct extension of infection from the spine or paraspinal tissues.
• Sources of hematogenous infection
  • Skin and soft tissue
  • Infected catheter
  • Bacterial endocarditis
  • Respiratory tract infection
  • Urinary tract infection
  • Dental abscess
  • Others
• Sources of contiguous spread
  • Vertebral osteomyelitis
  • Retropharyngeal abscess
  • Dermal sinus tract
  • Psoas abscess
  • Penetrating injury
  • Epidural injections or catheters

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