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New Nomogram Helps Clinicians Choose Initial Treatment of Spinal Epidural Abscess

Key findings

  • For patients with spinal epidural abscess, Massachusetts General Hospital researchers identified six independent factors that predict failure of nonoperative treatment
  • Notably, pretreatment motor deficit and sensory changes were strong risk factors for failure; these represent an advanced stage of disease with spinal nerve or cord compromise
  • The researchers developed a nomogram to help clinicians quantify the risk of failure

Advances in imaging have led to the earlier diagnosis of spinal epidural abscess, which has led to the improved efficacy of systemic antibiotic therapy in a number of cases. However, given the dangerous risk of neurologic compromise with spinal epidural abscess, it is crucial to avoid the failure of this therapy, and there are few data on which patients are at risk.

Using 24 years of data on patients with spinal epidural abscess, researchers at Massachusetts General Hospital identified six independent risk factors for failure of nonoperative management. In the Journal of Bone and Joint Surgery, they describe a nomogram they developed to help clinicians choose the initial therapeutic approach. Clinicians can use a nomogram to predict outcomes for individual patients by assigning points to a patient and disease characteristics.

Department of Orthopaedics Chief Mitchel B. Harris, MD, and Orthopaedic Spine Center Division Chief Joseph H. Schwab, MD, identified 472 adults with spinal epidural abscess who were initially treated nonoperatively at the discretion of the primary attending physician between 1993 and 2016. These patients were part of a larger cohort they reported on separately when investigating predictors of pretreatment motor deficit and 90-day mortality.

Nonoperative treatment was defined as systemic antibiotic therapy with or without CT-assisted percutaneous drainage. Patients classified as successfully treated were included if they had a follow-up examination greater than 60 days from onset of treatment. If patients had follow-up of less than 60 days but had a documented treatment failure they were included. 367 patients met the criteria (median age 59 years, 65% male).

Altogether, 99 (27%) of the 367 patients failed nonoperative management, and of those, 65 (66%) subsequently needed surgery. The median time to failure was 25 days.

Multivariable analysis yielded six independent predictors of failure of nonoperative treatment. The positive predictors were motor deficit at presentation, pathologic or compression fracture, active malignancy, diabetes mellitus and sensory changes.

Dr. Schwab's team developed a nomogram to help clinicians quantify the probability of failure of nonoperative treatment.

Table Points per Predictor

Figure 1: Points given for each independent predictor used for the nomogram

In this case, clinicians should total the points for each patient according to the table in Figure 1, then use the following equation to calculate the risk of failure:

Probability = econstant + (total points x points coefficient)/1 + econstant + (total points x points coefficient)

The constant is −1.95 and the points coefficient is 0.21.

The researchers stress that for patients with spinal epidural abscess, the initial choice between surgery and nonoperative management is crucial because of the poorer prognosis of patients who fail nonoperative management. Other studies have identified additional risk factors for failure that clinicians should be aware of:

  • Age >65 years
  • Methicillin-resistant Staphylococcus aureus infection
  • White blood cell count >12.5 x 103 cells/mL
  • Positive blood cultures
  • C-reactive protein level >115 mg/L

The research team emphasized that the study findings do not imply the efficacy of surgery. The study design did not allow for conclusions about the comparative efficacy of operative versus nonoperative management of spinal epidural abscess.

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