Spinal epidural abscess (SEA) is a challenging diagnosis to make in the Emergency Department (ED), with a diagnostic delay occurring in about 75% of patients.[1] To ultimately make a diagnosis of SEA, patients typically require an MRI, and so physicians may often have diagnostic hesitancy, as MRI’s are such a challenging test to obtain in the ED. Here, we will take a deeper look at the evidence surrounding spinal epidural abscess, to develop a more consistent approach to this patient population.

Pathophysiology

Spinal epidural abscess primarily develops as a result of hematogenous spread from other infectious sources, however, contiguous infectious spread, postoperative infection and trauma are also cited as potential inciting factors for the development.[2] The most common pathogen isolated in SEA is Staphylococcus aureus, while other agents include Mycobacterium tuberculosis, Haemophilus influenzae, Brucella and Actinomyces.[2]

Risk Factors

It is estimated that the vast majority of patients (90-98%)[1,3] have at least one risk factor for SEA, making these features an critical part of the consideration in patients with back pain.

• IVDU
• Immunocompromise, alcoholism, diabetes
• Recent paraspinal procedure
• Infection of adjacent structures
• Trauma
• Malignancy
• Recent delivery
• Autoimmune conditions: SLE, CKD, spondylosis, colitis.

Clinical Features

The “classic triad” of fever, back pain and neurologic deficit is only present in roughly 10-15% of patients.[1] The vast majority of patients will also have a normal neurologic examination. The back pain these patients experience tends to be very focal, rather than diffuse pain often seen in MSK pathology, but this can be difficult to discern.

There is utility to some bloodwork [4]:

• A WBC is not particularly helpful in the vast majority of cases
• CRP has an sensitivity of 85%, specificity of 50%
• ESR has a sensitivity of 100%, specificity of 75%
• 95% of patients with SEA have an ESR > 20
• Extremely high ESR (>110) and thrombocytopenia has a rather poor prognosis associated with it.

When should I worry about it?

As with most rare diagnostic entities, be aware of risk factors for this condition, and when they are present, use physical exam and laboratory findings to help you better risk stratify your patient. Obviously, as it is a rare disease, every patient with a risk factor and back pain does not have a SEA, so we still need to maintain a reasonable testing threshold. The diagnosis is probably most easily made in IVDU, but it is important to maintain an high index of suspicion with any patient with an risk factor documented above.

Another important consideration is to be wary of the back pain patient with UTI symptoms. Since SEA often occurs as a result of hematologic spread, these patients may develop Staph a. urinary tract infections.

There are 4 stages to the clinical presentation of SEA:

• Stage 1: Back pain (focal, severe), fever, tenderness
• Stage 2: Radicular pain, reflex changes, nuchal rigidity
• Stage 3: Cauda equina symptoms
• Stage 4: Paralysis – once this occurs, it is often irreversible

MRI would be the diagnostic test of choice for spinal epidural abscess, with a sensitivity greater than 90%. CT scans, may be helpful in the diagnosis of vertebral osteomyelitis or discitis, but unfortunately lacks sensitivity when the clinical concern is for SEA.

Ultimately, in approaching these patients:

• Assess for risk factors, not ‘classic’ features
• Do an appropriate neurologic exam
• Consider ESR/CRP as an important assessment tool to gather further clinical data to better assess your pretest probability
• Sometimes, you need to advocate for your patient to have an MRI.
• In the patient with multiple visits for ‘mechanical back pain’ – consider the possibility of SEA on your differential diagnosis

• These patients require treatment with urgent surgical decompression and antibiotics (typically; Vancomycin and Ceftriaxone, with Flagyl if the patient is post operative).