use MRI instead of CT to scan for epidural abscess
- related: Infectious Disease ID
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This patient likely has an infection in or adjacent to the spinal column, whether discitis with vertebral osteomyelitis and phlegmon in the adjacent musculature or a frank epidural abscess. Depending on the circumstances, such an infection may require an intervention for source control. Improperly treated, spinal epidural abscess may impinge on the spinal cord and/or nerve roots, resulting in serious neurological disability. CT scanning is an insensitive test for spinal epidural abscess, and the most appropriate next step is MRI of the spine. Because these infections may extend across multiple sections of the spine, it is common to image the lumbar and thoracic, and even the cervical spine to define the extent of the infection. In this patient, after MRI confirmed epidural abscess, rereview of the CT scan suggested the possibility of vertebral osteomyelitis and adjacent phlegmon.
While spinal epidural abscess is rare, particularly in normal hosts, risk factors include diseases as common as diabetes. Impaired immunity, high risk for bacteremia (eg, through indwelling vascular devices, hemodialysis, or IV drug use), and instrumentation or implanted hardware in the spine are all important risk factors. About one-half of the time, the infection is from hematogenous spread, while around one-third of the time it is contiguous spread, which is particularly observed after procedures on the spine. Historically, a triad of fever, focal back pain, and neurological deficits was considered diagnostic of epidural abscess, although the triad is insensitive and nonspecific. Evaluation should not be delayed until neurological deficits are observed; presence of neurological deficits strongly increases the urgency of making the diagnosis and considering surgical intervention.
By far, the most common cause of epidural abscess is Staphylococcus aureus, both methicillin-sensitive and methicillin-resistant. However, other gram-positive organisms, as well as gram-negative organisms (and multiple simultaneous infections), can cause the infection, particularly in the context of surgery and/or indwelling foreign bodies. Historically, chronic, untreated pyelonephritis occasionally caused adjacent epidural abscess, although this is uncommon in the present day.
Management is generally a combination of medical therapy and source control. The bacteremia may be severe, and secondary infections may occur (eg, septic arthritis or endocarditis). Extensive workup may be required to rule out metastatic loci of infection; some preliminary evidence suggests that patient outcomes may be better with infectious disease consultation in the setting of S aureus bacteremia.
The patient’s hydronephrosis is likely related to his prostatism and is unlikely to be pathological in this case. Even if pyelonephritis may have been present, it would not eliminate the need for evaluation of the spine with MRI. 12