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Emergency Medicine News:
doi: 10.1097/01.EEM.0000381473.07156.08
ID Rounds

ID Rounds: Think Spinal Epidural Abscess in Nontraumatic Back Pain

Isaacs, Lawrence MD

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Spinal epidural abscess (SEA) is a rare but potentially devastating disease. A collection of pus between the dura matter and the vertebral body, it usually occurs from hematogeneous spread but also from a vertebral osteomyelitis via direct extension. This is an important diagnosis to consider in any patient with nontraumatic back pain, especially in those at risk for developing an abscess. Without prompt diagnosis and treatment, the patient can be left with devastating sequela such as permanent neurological deficits or death.

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Risk factors for developing an SEA include being male, over age 30 (though it can occur at any age), IV drug use, alcoholism, spinal intervention, COPD, chronic renal failure, HIV, diabetes, hypertension, morbid obesity, spinal trauma, having an indwelling catheter, skin abscess, and transient bacteremia (any cause). (Lancet Neurol 2009; 8[3]:292.)

Diabetes seems to be an important risk factor; it has been associated in as many as 50 percent of cases of SEA, although no cause is found in up to 40 percent. (Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 7th ed. London: Elsevier; 2009.) It most commonly affects the thoracic or lumbar spine, but can occur in the cervical spine. The classic triad of fever, back pain, and neurological deficit does not present consistently, especially early in the disease. (Some say less than 20% of the time. J Emerg Med 2004; 26[3]:285.) Back pain seems to be the most consistent complaint in SEA patients. A typical course usually starts with back pain and tenderness, progressing to radicular pain and paresthesias, and then to spinal cord dysfunction (focal deficits: motor and sensory) and paraplegia. Pain is reported in approximately 70 percent to 90 percent of cases, with fever found in 60 percent to 70 percent. (Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 7th ed. London: Elsevier; 2009.) Depending on the cause, sometimes there is an associated adjacent osteomyelitis or discitis. These can be postoperative infections (discectomies or lumbar punctures) or from hematogeneous spread. The time course of symptoms is usually days to weeks.

The examination of a patient with an SEA depends on the extent of the abscess, its level, and whether it is early or later in the disease. Most abscesses involve three to four vertebrae, but in rare cases, the whole spine may be involved. (Am J Emerg Med 2009;27[4]:514.e7-9.) Besides the classic triad, meningismus, radicular pain, and bowel and bladder dysfunction may be present. Look for a reason for developing an SEA: recent surgery, epidural catheter, abscess, or IV drug use.

The laboratory workup in a suspected case should include a CBC, blood cultures, and a sedimentation rate (ESR). Blood cultures are important because of the strong correlation between the organisms obtained via the blood culture and abscess. (Emerg Med Clin North Am 2003;21[4]:1089.) The CBC is not reliably abnormal, but the ESR is usually elevated. (J Emerg Med 2004;26[3]:285.) If a further workup is warranted, a MRI with gadolinium is the study of choice. If an MRI is not available or contraindicated, a CT myelogram is indicated.

The microbiology of an SEA weighs heavy toward gram-positives, with Staphylococcus and Streptococcus accounting for the vast majority of cases. Staphylococcus aureus currently accounts for approximately 60 percent of all SEAs. (Lancet Neurol 2009;8[3]:292.) Depending on the source and patient risk factors, gram-negatives, Mycobacterium tuberculosis, Pseudomonas, and fungi are all documented causes for an SEA. Pseudomonas has been strongly associated with injection drug use. (J Spinal Disord Tech 2007;20[4]:324.) One case also reports an SEA in a 5-year-old from cat scratch disease (Bartonella henselae).

ED treatment begins with appropriate broad-spectrum antibiotics and neurosurgical consultation. Reasonable empiric choices are gram-positive coverage that includes MRSA such as vancomycin and broad gram-negative coverage (cefepime, ceftazidime, or meropenem). Definitive treatment is drainage of the abscess, either guided by CT or open surgical decompression depending on the size of the abscess. If the patient is exhibiting any neurological deficits, this is a surgical emergency. The duration of antibiotic treatment is usually four to six weeks

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Risk Factors and Microbiology for SEA

* IV drug use: Staphylococcus aureus, Pseudomonas aeruginosa

* Diabetes mellitus: Multiple

* Multiple medical illnesses: Multiple

* Recent invasive spinal procedures: S. aureus, Staphylococcus epidermidis

* Penetrating spinal trauma: S. aureus, S. epidermidis

* Morbid obesity: Multiple

* Immunosuppression: Bacterial, mycobacterial, fungal

* Skin infections or abscesses: S. aureus, S. epidermidis

* Transient bacteremia: Multiple

Adapted from Lancet Neurol 2009;8(3):292.

Dr. Isaacs is a clin...
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