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Three Part Question

In [adult patients presenting to the emergency department with undifferentiated back pain], is there an [effective screening tool] to decide if [specialized imaging is required for diagnosis of a bacterial spinal epidural abscess]?

Clinical Scenario

A 40 year old male, with a history of IV drug use, comes to the emergency department with five days of back pain. He has no history of trauma, fevers, or neurologic complaints. As an IV drug user, he has a risk factor for a BSEA, but is afebrile and is neurologic exam is non-focal. Does he need an MRI?

Search Strategy

Ovid MEDLINE 1950 to July Week 5 2009
exp Epidural Abscess/ep [Epidemiology] and exp Epidural Abscess/ep [Diagnosis]

All EBM Reviews - Cochrane DSR, ACP Journal Club, DARE, CCTR, CMR, HTA, and NHSEED - No hits with tree for Epidural Abscess

Search Outcome

Numerous case reports and case series are available for bacterial spinal abscesses. There are no EBM reviews for this disease. Only one study retrospectively reviewed emergency department patients with bacterial spinal epidural abscesses to examine presenting signs/symptoms. Details of this paper are show in table 1.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Davis, DP, Wold, RM, Patel, RJ, et al 2004 USA	63 adult ED patients diagnosed with BSEA over 10 year study period	Retrospective review with matched case controls	Analysis of presenting signs/symptoms of SBEA	The classic triad of back pain, fever, and neurologic deficits had a 99% specificity, but only a 8% sensitivity. Neck or back pain was the chief complaint in 95% of SEA patients. Only 33% of patients reported a history of fever (T>38.0), with 13% febrile in the ED. The neurologic exam was normal in 68% of patients. 98% of patients with BSEA had at least one risk factor , with a negative predictive value of 99%. Presence of one or more of the following (98%): Intravenous drug use (60%), Immunocompromised (21%), Alcohol Abuse (19%), Recent spine procedure (16%), Distant site of infection (14%), Diabetes (13%), Indwelling catheter (11%), Recent spine fracture (3%), Chronic renal failure (3%), Cancer (3%) Risk factors can be categorized as either a source for infection or an underlying systemic disease. IV drug use was the most commonly identified risk factor. The white blood cell count was elevated above 10,000 in 60% of patients, demonstrating a poor sensitivity. The ESR was elevated above 20 mm/hr (median=77) in 98% of patients though this data was often not obtained until after admission. Blood cultures were positive in 57% with Staph. aureus as the most common organism. According to the study’s analysis, 50 patients with back pain and at least one risk factor by history would need to be screened to identify one patient with a BSEA.	Retrospective, possible selection bias of controls

Comment(s)

The classic triad of back pain, fever, and neurologic deficits had a 99% specificity, but only a 8% sensitivity. Neck or back pain was the chief complaint in 95% of SEA patients. Only 33% of patients reported a history of fever (T>38.0), with 13% febrile in the ED. The neurologic exam was normal in 68% of patients. 98% of patients with BSEA had at least one risk factor (see table 2), with a negative predictive value of 99%. Risk factors can be categorized as either a source for infection or an underlying systemic disease. IV drug use was the most commonly identified risk factor. The white blood cell count was elevated above 10,000 in 60% of patients, demonstrating a poor sensitivity. The ESR was elevated above 20 mm/hr (median=77) in 98% of patients though this data was often not obtained until after admission. Blood cultures were positive in 57% with Staph. aureus as the most common organism. According to the study’s analysis, 50 patients with back pain and at least one risk factor by history would need to be screened to identify one patient with a BSEA.

Clinical Bottom Line

If a patient with back pain does not have a risk factor for BSEA, further work-up for BSEA is not necessary. If the patient has a risk factor and either a fever (measured in ED or by history) and/or a neurologic deficit, diagnostic imaging is likely warranted. If the same patient is afebrile and without neurologic abnormalities, an elevated ESR may lower the threshold to obtain advanced imaging.

References

1. Davis, DP, Wold, RM, Patel, RJ, et al The clinical presentation and impact of diagnostic delays on emergency department patients with spinal epidural abscess J Emerg Med 2004; 26:285