A history of recent or remote trauma often may mask the diagnosis of rare causes of back pain such as spinal epidural abscess (SEA).⁴ Of the epidural spinal cord compressive syndromes, defined as radiologic indentation of the thecal sac,^5,6 SEA composes approximately 0.2-2 cases per 10,000 hospital admissions⁷ or less than 1 case per million residents, thereby limiting many physicians’ experience with the diagnosis of this potentially debilitating cause of back pain.

Pathophysiology

SEA is a suppurative process confined within the epidural space, lying between the dura mater and the vertebral periosteum. The incidence of SEA is increasing in developed countries^8-11 likely because of an aging population, greater numbers of spinal procedures, drug abuse, and increased use of immunosuppressive agents and antibiotics, all of which contribute to an altered immune state.¹²

SEA affects patients of all ages, though the majority are between 30 years and 60 years old, with a predominance of males.⁷ SEA most often results from hematogenous dissemination from many sources, including skin or soft tissue infection (most common), respiratory tract infection (especially in pulmonary tuberculous), urinary tract infection, or bacteremia. In some cases, it is not possible to identify the origin.¹³ Hematogenous spread usually results in an abscess located posteriorly (80% of cases), whereas direct extension from retropharyngeal and/or retroperitoneal infection typically results in a more anterior spinal location (20% of cases).

The most common organism isolated is Staphylococcus aureus (60%-90%),^14,15 although Gram-negative bacteria are more common in intravenous drug users.^7,16 Interestingly, individuals who use intravenous drugs have been found to have higher carrier rates of S. aureus than the general population. Thus, the source of SEA pathogen in IVDU patients may be their chronic carrier state rather than the paraphernalia itself.^10,17-19

SEA more commonly affects the thoracic and lumbar spine, where the epidural space is wider. There is a more extensive extradural venous plexus, with an average abscess extension of 3-5 spinal cord segments.²⁰ SEA may present with symptoms measured in hours to days (acute) or weeks to months (chronic), or a combination of both.¹³ Neurologic symptoms are generally thought to result from mechanical compression, but the exact mechanism of spinal cord necrosis is still unclear. Some authors suggest vasculitis, thrombosis, and/or compression of the spinal vessels with resultant hypoxia as either a contributing factor or primary mechanism.^21-24

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