Spinal Epidural Abscess

Epidemiology

  • Incidence: 2-25 cases per 100k hospital admissions (or 0.88 cases per 100k person-years)
    • Factors Contributing to Inceasing Incidence of Spinal Epidural Abscess Over the Last 20-30 Years
      • More Sensitive Diagnostic Modalities: such as spine MRI
      • Aging Population
      • Increasing Use of Invasive Spine Procedures
      • Increasing Use of Vascular Access
      • Increased Injection Drug Abuse (IVDA)
  • Median Age of Onset: 50 y/o
    • Highest prevalence between 50-70 y/o
    • Age range: 10-87 y/o
  • Sex: M:F ratio is 1:0.6
    • Higher incidence in males is related to higher prevalence of the reported risk factors in males

Risk Factors for Spinal Epidural Abscess


Spinal Cord Anatomy and Physiology

Spinal Cord

  • Conus Medullaris: the spinal cord tapers and ends between L1 and L2, with the conus medullaris representing the most distal bulbous part of the spinal cord
    • Blood Supply
      • Spinal arteries (anterior median longitudinal arterial trunk and 2 posterolateral trunks): main supply
      • Radicular Arterial Branches from Aorta: less prominent arterial supply
      • Lateral Sacral Artery: less prominent arterial supply
      • Fifth Lumbar Artery: less prominent arterial supply
      • Iliolumbar Artery: less prominent arterial supply
      • Middle Sacral Artery: less prominent arterial supply
  • Cauda Equina (“horse tail”): mass of lower lumbar and S1-S5 nerve roots distal to the conus medullaris (and within the subarachnoid space)
    • Sensory Innervation: to the saddle area (perineal dermatomes) and lower extremity dermatomes
    • Motor Innervation
      • S2-S4 -> inferior rectal nerve -> voluntary muscles of external anal sphincter
      • S2-S4 -> pudendal nerve -> voluntary muscles of urethral sphincter
      • Lower extremity myotomes
    • Parasympathetic Innervation: to the bladder and lower part of the colon (from splenic flexure to the rectum)
      • S2-S4 -> pelvic splanchnic nerves -> detrusor muscle of bladder
    • Compression of the cauda equina technically represents a “peripheral” nerve injury
    • Blood Supply: middle sacral artery
  • Filum Terminale: the fibrous (non-neural) extension of the spinal cord, which extends down to the coccyx

Epidural Space

  • Posterolateral Epidural Space
    • Anatomy
      • Posterolateral epidural space extends vertically down the spinal canal and contains arteries, venous plexus, and fat
      • Posterolateral epidural space is larger than the anterior epidural space
      • Posterolateral epidural space is larger in the sacral region than it is in the cervical region
    • Posterolateral Epidural Abscess
      • Posterior epidural abscess is more common than anterior epidural abscess, due to larger size of the posterior epidural space (with more infection-prone fat) and a more extensive venous plexus (which allows microbiologic seeding of the space)
      • Thoracolumbar posterior epidural abscess is the most common location in the spine, due to larger size of the epidural space (with more infection-prone fat)
      • Vertical extension of abscess commonly occurs: average extent of extenson is 3-5 spinal cord segments (although some cases manifest pan-spinal infection)
      • Lumbar epidural abcsess is predisposed by the use of epidural procedures for pain management
  • Anterior Epidural Space
    • Anatomy
      • Anterior epidural space is a virtual space under normal circumstances (due to adherence of dura to bone of vertebral bodies from the foramen magnum down to L1)
    • Anterior Epidural Abscess
      • Anterior spinal epidural abscess usually occurs below L1 (due to adherence of dura to bone of vertebral bodies from the foramen magnum down to L1)
      • Anterior spinal epidural abscess is usually associated with vertebral osteomyelitis

SPINAL CORD


Etiology

Bacteremia with Hematogenous Spread to Epidural Space (approximately 50% of cases)

  • Acupuncture
  • Indwelling Vascular Access Device
  • Intravenous Drug Abuse (IVDA)
    • The location of spinal epidural abscess is correlated with the sites of injection: cervical spinal epidural abscess is more common in those with upper extremity injection sites, while lumbar spinal epidural abscess is more common in those with lower extremity injection sites
  • Pneumonia (see Pneumonia, [[Pneumonia]])
  • Sepsis (see Sepsis, [[Sepsis]])
  • Skin/Soft-Tissue Infection
  • Tattoos
  • Urinary Tract Infection (UTI) (see Urinary Tract Infection, [[Urinary Tract Infection]])

Contiguous Spread to Epidural Space (approximately 33% of cases)

  • Direct Inoculation Into Epidural Space
    • Epidural Anesthesia: 0.5-3% of cases are complicated by spinal epidural abscess
      • Short-term epidural catheter use (as in obstetrical cases) is associated with significantly decreased risk (study cited only one case in 506k obstetric epidural cases)
      • Epidural space infection can occur via multiple possible mechanisms: infection at time of catheter placement, ascending contamination from skin flora, contaminated syringes or injected solutions, or from bacteremic seeding while catheter is in place
    • Nerve Block
    • Spinal/Paraspinal Steroid/Analgesic Injection
    • Spinal Stimulator
    • Spinal Surgery
  • Psoas Muscle Abscess (see Psoas Muscle Abscess, [[Psoas Muscle Abscess]])
  • Spinal Degenerative Joint Disease
  • Spinal Trauma
  • Vertebral Osteomyelitis (see Osteomyelitis, [[Osteomyelitis]])
  • Vertebral Pyogenic Discitis (see Discitis, [[Discitis]])

Unknown Portal on Entry Into Epidural Space (up to 17% of cases)

  • Unclear Source

Physiology

Patterns of Spread To/From Epidural Space

  • Spread of Infection to Epidural Space: bloodstream/contiguous infection can spread to the epidural space (as noted above)
  • Spread of Infection from Epidural Space : epidural abscess can spread contiguously or through the bloodstream to other sites
  • Vertebral Osteomyelitis or Discitis: coexistent with epidural abscess in up to 80% of cases

Mechanisms of Spinal Cord Injury in Spinal Epidural Abscess

  • Direct Spinal Cord Compression by Pus or Granulation Tissues (primary mechanism)
    • Granulation tissue is more common when abscess has been present for at least 2 weeks
    • Animal models suggest that compression and ischemia have additive effects on neurologic function
  • Bacterial Toxins/Inflammation with Acute Myelitis [MEDLINE]
  • Septic Thrombophlebitis
  • Vasculitis/Interruption of Arterial Blood Supply to Spinal Cord: spinal cord infarction can be caused by compression and/or septic thrombophlebitis

Microbiologic Etiology

  • Staphylococcus Aureus (see Staphylococcus Aureus, [[Staphylococcus Aureus]]): 66% of cases
    • 21-40% of Staphylococcus Aureus cases are methicillin-resistant Staphylococcus aureus (MRSA): the incidence of MRSA and MRSA-epidural abscess cases has increased in the past decade
      • MRSA is partcularly common in patients with spinal or other implantable devices
      • Spinal epidural abscess outcomes are worse with MRSA than with non-MRSA Staphylococcus aureus
  • Gram-Negative Rods: 16% of cases
    • Escherichia Coli (see Escherichia Coli, [[Escherichia Coli]]): associated with urinary tract infection (UTI)
    • Pseudomonas Aeruginosa (see Pseudomonas Aeruginosa, [[Pseudomonas Aeruginosa]]): associated with IV drug abuse
  • Streptococcus (see Streptococcus, [[Streptococcus]]): 9% of cases
  • Staphylococcus Epidermidis (see Staphylococcus Epidermidis, [[Staphylococcus Epidermidis]]): 3% of cases
    • Risk is increased with spinal procedures/instrumentation (epidural catheters, glucocorticoid injections, spinal surgery), penetrating spine trauma, and skin infections
  • Actinomycosis (see Actinomycosis, [[Actinomycosis]])
  • Nocardiosis (see Nocardiosis, [[Nocardiosis]])
  • Anaerobes: 2% of cases
  • Mycobacteria
  • Fungi/Parasites: 1% of cases
  • Unknown: 6% of cases

Diagnosis

  • CBC
    • Leukocytosis: present in 60% of cases (at initial presentation)
  • Erythrocyte Sedimentation Rate (ESR): elevated >20 mm/hr in most cases
    • High sensitivity
    • Low specificity: 33% of patients with back pain not due to spinal epidural abscess have an elevated ESR
    • Mean ESR Elevation: 76.5 mm/hr in one study
  • C-Reactive Protein (CRP): elevated in most cases
  • Blood Cultures: positive in 60% of cases
    • Cases associated with Staphyloccoccus aureus are more likely to have positive blood cultures
  • Spine X-Rays: usually not helpful
    • However, may reveal co-existent osteomyelitis
  • Spine MRI with Gadolinium
    • High sensitivity: >90%
    • High specificity
    • Best imaging modality
      • Useful to delineate the paraspinal and longitudinal aspects of the epidural abcsess, facilitating surgical planning
      • Useful to differentiate abscess from malignancy
      • May reveal coexistent osteomyelitis or discitis
    • T1-Weighted Images: epudiral abscess appears hypodense
    • T2-Weighted Images: epidural abscess appears hyperintense
  • Spine CT with IV Contrast: alternative to MRI
    • May reveal coexistent osteomyelitis or discitis
  • CT Myelogram: no longer used
  • Radionuclide Scanning (technetium, gallium, indium): although these may demonstrate increased uptake, they have high false-negative rates
  • Epidural Abscess Cultures: positive in 90% of cases
  • Lumbar Puncture/CSF: lumbar puncture (that might be performed to rule out meningitis/encephalitis) should be performed only after after spine MRI rules out the presence of an epidural collection that might be traversed by the needle (due to the risk of disseminatng the infection) [MEDLINE]
    • Lumbar puncture can also result in neurologic deterioration if if is perfomed below the site of a complete spinal subarachnoid block
    • CSF Gram Stain: almost always negative
    • CSF Cultures: positive in <25% of cases
      • Blood cultures are usually positive in cases with positive CSF cultures
    • CSF Cell Count: pleocytosis may be seen (either polymorphonculear or mononuclear-predominance)
    • CSF Protein: non-specific elevation may be seen

Clinical

Classical Triad of Clinical Symptoms/Signs

  • General Comments: classical triad is uncommon at initial presentation
  • Fever (see Fever, [[Fever]])
  • Localized Back Pain (see Back Pain, [[Back Pain]]): most common presenting symptom
  • Neurologic Deficits

Clinical Stages

  • General Comments: clinical stages are variable, unpredictable, and may occur out of sequence (even in the presence of appropriate antibiotic therapy)
  • Stage 1: severe back pain and fever
  • Stage 2: spinal irritation and radicular pain
  • Stage 3: fecal and urinary incontinence
  • Stage 4: paralysis

Typical Clinical Symptoms/Signs

  • Abdominal Pain (see Abdominal Pain, [[Abdominal Pain]]): may occur in thoracic spine epidural abscess
  • Fever (see Fever, [[Fever]])
  • Back (75% of cases) (see Back Pain, [[Back Pain]])
    • Common in lumbar epidural abscess
    • Usually focal and severe, occurs early
    • Diagnostic Guidelines for Evaluation of Back Pain in the Emergency Department: evaluation with risk factor assessment and CRP/ESR testing prior to imaging has been shown to decrease diagnostic delay and decrease motor deficits at the time of diagnosis in spinal epidural abscess [MEDLINE]
  • Chest Pain (see Chest Pain, [[Chest Pain]]): may occur in thoracic spine epidural abscess
  • Fever (50% of cases) (see Fever, [[Fever]])
  • Neck Pain (see Neck Pain, [[Neck Pain]]): commonly occurs in cervical epidural abscess
  • Root Pain: with character of “shooting” or “electric shocks” in distribution of the affected nerve root, may appear later
  • Neurologic Symptoms (33% of cases): typically these are late findings
    • Cauda Equina Syndrome (see Cauda Equina Syndrome, [[Cauda Equina Syndrome]]): for cases with involvement of cauda equina (cauda equina is the mass of lower lumbar and S1-S5 nerve roots distal to the conus medullaris)
      • Areflexia
        • Ankle
      • Bladder/Bowel Dysfunction
        • Decreased Anal Tone/Fecal Incontinence
        • Urinary Retention: due to detrusor muscle weakness
        • Urinary Incontinence
      • Low Back Pain/Sciatica: sciatica may be unilateral or bilateral
      • Variable Lower Extremity Sensory/Motor Dysfunction
      • Lower Extremity Weakness: bilateral or unilateral
      • Lower Extremity Paraplegia: bilateral or unilateral
      • Saddle Anesthesia: involving genitals, uretha, anus, and inner thighs
      • Sexual Dysfunction
    • Weakness/Paralysis: once present, may quickly become irreversible

Misdiagnosis/Mismanagement of Epidural Abscess [MEDLINE]

  • Frequency of Misdiagnosis of Epidural Abscess: up to 75% of cases are initially misdiagnosed
  • Factors Contributing to Misdiagnosis/Mismanagement of Epidural Abscess
    • Spine MRI of Wrong/Unaffected Area of the Spine
    • Identification of Only One of Multiple Non-Adjacent Epidural Abscesses
    • Ascribing All Clinical/Laboratory Findings to Vertebral Osteomyelitis
    • Inability to Assess Sensorimotor Function (Due to Altered Mental Status/Sedation/Poor Patient Cooperation)
    • Clinician Unawareness of Urgency of Diagnosis/Treatment
    • Surgical Management of Spinal Stimulator-Associated Abscess by Removing Only Part of the Device
    • Treatment of Staphylococcus Aureus Bacteremia Without Identifying the Source/Potential Metastatic Foci of Infection

Complications

  • Sepsis (see Sepsis, [[Sepsis]])
  • Decubitus Ulcer (see Decubitus Ulcer, [[Decubitus Ulcer]])
  • Deep Venous Thrombosis (DVT) (see Deep Venous Thrombosis, [[Deep Venous Thrombosis]])
  • Irreversible Paraplegia: occurs in 4-22% of cases
    • Usually related to delayed diagnosis and/or suboptimal management
  • Urinary Tract Infection (UTI) (see Urinary Tract Infection, [[Urinary Tract Infection]])
  • Pneumonia (see Pneumonia, [[Pneumonia]]): in cases with cervical epidural abscess

Treatment

Neurosurgical Drainage/Evacuation of Inflammatory Tissue

  • Therapeutic Procedure of Choice: surgical evacuation is considered the standard of care to both relieve the cord compression and control sepsis
  • Predictors of Neurologic Outcome: extent and duration of neurologic deficit prior to surgery
  • Possible Contraindications to Surgery: while a non-surgical strategy can be used in very select patients (for example: those without neurologic defiicts), it requires close monitoring for potential neurologic deterioration (allowing for prompt surgical intervention at that point in time)
    • Patient Refusal to Undergo Surgery
    • Medical Contraindications to Surgery
    • Presence of Advanced Neurologic Deficits Which are Unlikely to Improve with Surgery: complete paralysis >24-48 hrs duration
    • Large Extent of Spinal Involvement/Panspinal Involvement: which may make surgery impractical (although in these cases, a limited surgical exposure with cranial/caudal placement of epidural catheters may be utilized)
    • Absence of Neurologic Deficits
  • Timing of Surgery:: surgery should be performed as soon as possible (generally within 24-36 hrs)
    • Rate of progression is unpredictable
    • Paralysis present for >24 hrs is unlikely to improve with surgical decompression

Therapeutic Needle Aspiration of Epidural Abscess

  • May be considered in select cases without evidence of cord compression

Antibiotics

  • Length of Treatment: prolonged course with IV antibiotics is required (usually 6-8 weeks or until resolution of abscess on MRI)
  • Empiric Therapy: Vancomycin IV + Metronidazole IV + Ceftriazone/Cefotaxime/Ceftazidime IV
  • Targeted Therapy: guided by blood cultures, needle aspiration of abscess, or surgical cultures
  • Methicillin-Senstitive Staphylococcus Aureus (MSSA)-Specific Therapy
    • Nafcillin/Cefazolin (see Nafcillin, [[Nafcillin]] and Cefazolin, [[Cefazolin]]): these have better activity than Vancomycin against MSSA
  • Methicillin-Resistant Staphylococcus Aureus (MRSA)-Specific Therapy
    • Vancomycin IV (see Vancomycin, [[Vancomycin]]): relatively poor CSF penetration of inflammed meninges, better with inflammed meninges
    • Linezolid IV (see Linezolid, [[Linezolid]]): alternative to Vancomcyin
    • Daptomycin IV (see Daptomycin, [[Daptomycin]]): alternative to Vancomcyin
    • Tigecycline IV (see Tigecycline, [[Tigecycline]])

Removal of Spinal Hardware

  • Removal of entire spinal neurostimulator is required in these cases

Corticosteroids (see Corticosteroids, [[Corticosteroids]])

  • May be used in select cases to decrease spinal edema in cases with progressive neurologic compromise pre-operatively

Post-Acute Care

  • Follow-Up Spine MRI: usully indicated at about 4 wks into therapy (or earlier, if neurologic deterioration occurs)
  • Spinal Cord Rehabilitation: may lead to moderate-marked improvement in motor function in some cases, even up to a year later

Prognosis:

  • Mortality Rate: 5% (usually due to sepsis, uncontrolled meningitis, or other underlying co-morbid illness)
  • Recurrence of Epidural Abscess: may occur in successfully-treated cases who are subsequently treated with immunosuppressives (glucocorticoids, etc) or later become immunocompromised

References

  • Decreased morbidity from acute bacterial spinal epidural abscesses using computed tomography and nonsurgical treatment in selected patients. Ann Neurol 1985, 17:350–355 [MEDLINE]
  • Nonoperative treatment of spinal epidural infections. J Neurosurg 1989, 71:208–210 [MEDLINE]
  • Spinal epidural abscess: a ten-year perspective. Neurosurgery 1990, 27:177–184 [MEDLINE]
  • Serious non-fatal complications associated with extradural block in obstetric practice. Br J Anaesth. 1990 May;64(5):537-41 [MEDLINE]
  • Spinal epidural abscess: a review of epidemiology, diagnosis, and treatment. J Spinal Disord 1999, 12:89–93 [MEDLINE]
  • A retrospective study of surgical and conservative treatment for spinal extradural abscess. Eur Spine J 2000, 9:67–71 [MEDLINE]
  • Spinal epidural abscesses: clinical manifestations, prognostic factors, and outcomes. Neurosurgery 2002, 51:79–85; discussion 86–77 [MEDLINE]
  • Spinal epidural abscess. N Engl J Med 2006; 355: 2012-20 [MEDLINE]
  • Spinal epidural abscess in clinical practice. Q J Med 2008; 101: 1–12 [MEDLINE]
  • Management of a spontaneous spinal epidural abscess: a single-center 10-year experience. Neurosurgery 2009, 65:919–923; discussion 923–914 [MEDLINE]
  • Spinal epidural abscess. J Emerg Med 2010; 39(3): 384–390 [MEDLINE]
  • Spinal epidural abscess: Current Diagnosis and Management. Curr Infect Dis Rep 2010; 12: 484-491 [MEDLINE]
  • Prospective evaluation of a clinical decision guideline to diagnose spinal epidural abscess in patients who present to the emergency department with spine pain. J Neurosurg Spine. 2011 Jun;14(6):765-70 [MEDLINE]