Epidural Abscess

Background

A spinal epidural abscess (SEA) can either compress or cause vascular compromise to the spinal cord or cauda equina. It produces sensory symptoms and signs, motor dysfunction, and, ultimately, paralysis and death. One half of cases are initially missed. It is increasing in frequency as IVDA increases. Males are affected slightly more then females with average age about 50 y/o.

The history is variable. The clinical triad of fever, back pain, and neurologic deficit is not present in most patients. 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. Symptoms may progress rapidly with abscesses from hematogenous spread or much slower if abscesses are from osteomyelitis or disci tis. The patient often gives a history of back strain or mild injury.

Risk factors include a skin or soft tissue infection, IVDA, 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 may 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 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.) Central cord syndrome from epidural abscess has also been reported.[9] 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.)

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

Anatomy

The spinal epidural space is not uniform. Abscesses occur more frequently in the larger, venous plexus containing posterior epidural space (allowing spread over several vertebral areas) and mostly in the thoracic area, which is the longest of the spinal regions. Anteriorly, it is a potential space with the dura tightly adherent to the vertebral bodies and ligaments.

Hematogenous spread with seeding of the epidural space is the suspected source of infection in most patients with sources including bacterial endocarditis, infected indwelling catheters, urinary tract infections, 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 inoculation 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 pathogen. MRSA is increasing particularly in patients with a history of MRSA abscesses, spinal surgery, or implanted devices. Immunosuppressed patients may have infections from unusual bacterial or fungal organisms. Environmental mold Exserohilum rostratum was the unusual pathogen associated with the outbreak of contaminated methylprednisolone.==

Differential Diagnosis

==Workup==Laboratory Studies CBC count, blood cultures, and preoperative lab studies. Leukocytosis is present in about two thirds of patients.[1] Elevated erythrocyte sedimentation rate (ESR): In one report, the mean ESR was 51 mm/h.[12] ESR may be highly elevated. Leukocytosis and ESR elevation are nonspecific laboratory findings and are not invariably present. Neither the presence of these findings nor the degree of laboratory abnormality is specific for spinal epidural abscess.[1] A treatment guideline incorporating ESR, C-reactive protein, and other risk factors has been proposed based on a small patient series.[13]