Spinal epidural abscess (SEA) is a surgical emergency that requires prompt diagnosis and treatment. It is generally a pyogenic infection and space-occupying lesion in the epidural space that causes neurologic sequel, including pain, paresthesias, paralysis, and even death. Bacteria can access the epidural space by direct extension from infected surroundings or, more commonly, from hematogenous seeding [17]. Abscesses can be located in the anterior or posterior space causing neurologic compromise from either direct compression or thrombosis of the vasculature. Spontaneous epidural abscess is rare, accounting for 0.2–2 cases per 10,000 hospital admissions per year [18, 19]. The incidence after central nerve block is quite varied and reported as 1:1000–1:100,000 [19]. In the literature, there is a definite prevalence for males with a male/female ratio of 1:0.56 [18].

In a meta-analysis of 915 patients with SEA, only 6% were attributed to either epidural anesthesia, injections in the epidural space, or spinal anesthesia [18]. The majority of patients will present with an identifiable source such as skin and soft tissue infections, indwelling catheters, frequent venous puncture, or spinal trauma/procedure.

Patients at increased risk of infection are more likely to develop an epidural abscess. Known risk factors for spinal epidural abscess are [18]:

As with many infectious processes, the initial manifestations of a spinal epidural abscess can be vague and nonspecific, presenting as malaise and fever. The diagnosis can be a challenge as it is quite rare among patients presenting with back pain. In a retrospective review of 46 patients who were diagnosed with SEA over a 10-year period, 89% had spinal pain, 67% had fever and chills, 57% had radicular pain, 37% had bowel or bladder dysfunctions, and 80% had paralysis (paraparesis, paraplegia) [20]. In an analysis of 871 patients, 71% had back pain, 66% had fever, 24% had incontinence, and 31% had paraplegia/paraparesis [18]. The combination of severe back pain as well as fever should be regarded as an early warning of SEA.

Fever and pain on palpation or) percussion may be noted. The neurological exam can be variable as the epidural abscess progresses. The clinical exam should include muscle strength testing, sensory testing, reflexes, and rectal exam.

The laboratory findings that are markers for severe inflammation or infection may accompany SEA; however, they are not all specific: leukocytosis, erythrocyte sedimentation rate (ESR), C-reactive protein (CPR), and thrombocytopenia . Patients presenting with an abscess will frequently have a leukocytosis [18, 20]. In a prospective study in Emergency Department patients, Davis et al. found that a treatment algorithm that incorporated risk factor assessment followed by erythrocyte sedimentation rate (ESR) and c-reactive protein (CRP) testing was highly sensitive and moderately specific for identifying patients with SEA [21]. They found the sensitivity and specificity for those with risk factors pointing toward SEA to be 100% and 67%, respectively. The mean CRP level was significantly higher in SEA patients than those with risk factor who were non-SEA. They found the rate of delayed diagnosis drops 80% after the implementation of this protocol.

While thrombocytopenia is not sensitive or specific for the diagnosis, it may be a risk factor for poor outcome [20]. The low platelet count, as seen in our patient, implies sepsis and the commencement of disseminated intravascular coagulation, thus more likely resulting in greater morbidity.

Lumbar puncture comes with significant risk, such as spread of the infection to the CSF and meninges. While it could yield information from the analysis of the CSF or even pus, radiologic imaging is preferred [19].

The plain film yields little utility in the initial evaluation of SEA, providing useful information in about 20% of cases [19]. However, abnormalities of the end plate should not be ignored as they can point toward an associated osteomyelitis [22]. A myelogram will reliably demonstrate a space-occupying lesion, but the same risks of lumbar puncture apply. While the computed tomography (CT) scan used to be the imaging modality of choice, the MRI is now the gold standard. Some recommend a full spinal MRI in the evaluation of suspected SEA [23]. The sensitivity of MRI is 91% compared to 92% with CT myelography [18]. However, MRI can be done without intervention and in all planes without moving a patient who may have neurologic compromise. It can also detect spinal and paraspinal infections [19]. The MR images will reveal a T1 hypointense and T2 hyperintense mass in the epidural space (Figs. 18.1 and 18.2). Gadolinium enhancement increases sensitivity and gives a better differentiation between the abscess and the surrounding neurologic structures (Fig. 18.3).