Spinal Epidural Abscess

Spinal epidural abscess is a collection of pus in the epidural space of the spinal canal that compresses the spinal cord or cauda equina and the blood supply to the cord. It is a neurosurgical and orthopaedic emergency, because outcome depends on the neurological state at the time of treatment, and diagnosis is often delayed.

The incidence is about 2 to 3 cases in 10 000 hospital admissions and is rising (older age, diabetes, injection drug use, spinal procedures and instrumentation). It peaks between 50 and 70 years, with a male predominance. Staphylococcus aureus causes 60 to 70% (MRSA in a growing share), then streptococci, Gram negative bacilli (including Pseudomonas in injection drug use), and rarely Mycobacterium tuberculosis, fungi and anaerobes.

About 50% have bacteraemia from another source (skin, urinary tract, endocarditis, dental infection), 20 to 30% follow a spinal procedure (epidural catheter, injection, surgery), and in up to a third no source is found.

Mortality is 5 to 20%. Permanent paralysis occurs in 20 to 40% of patients who present late. Complications are cord infarction, sepsis, vertebral osteomyelitis, spinal instability and kyphosis, and chronic pain.

Pathophysiology.

Bacteria reach the epidural space by haematogenous spread, by contiguous spread from vertebral osteomyelitis, psoas abscess or discitis, or by direct inoculation. Infection starts as a phlegmon and becomes an abscess. Neurological injury results from direct compression, venous congestion and thrombophlebitis, and arterial ischaemia of the cord. The thoracic and lumbar levels are most often affected (posterior collections are most common in the thoracic spine).

The classic triad of back pain, fever and neurological deficit is complete in only 10 to 15% at first presentation. Stages: (1) severe focal back pain with spinal tenderness, (2) radicular pain, (3) weakness, sensory loss and sphincter dysfunction, (4) paralysis. Progress from stage 2 to stage 4 can take hours. Fever is present in about 50%. Neck stiffness may appear with cervical abscess.

Examine the spine for percussion tenderness, full neurological state including power, sensation, reflexes, perianal sensation and anal tone, the skin (injection sites, pressure sores, cellulitis), heart (new murmur), and any catheters or implants. Grade neurological function (Frankel grade or equivalent) and record it before and after every intervention.

• ESR above 20 mm/hour in over 90% and raised CRP; white cell count is raised in about two thirds; procalcitonin may help to detect bacteraemia.
• Blood cultures (2 to 3 sets) before antibiotics: positive in 60 to 70%.
• MRI of the whole spine with gadolinium, immediately (sensitivity over 90%): rim enhancing collection or diffuse phlegmon, cord compression, cord signal change, vertebral osteomyelitis and discitis, skip lesions. Use CT myelography if MRI is contraindicated.
• Culture of pus at surgery or image directed aspiration (positive in 90%); biopsy of the disc or vertebra if osteomyelitis is present; mycobacterial and fungal cultures when indicated.
• Echocardiography for bacteraemia; HIV test, HbA1c, urinalysis, chest radiograph and renal function.

Differential diagnosis.

• Vertebral osteomyelitis and discitis without epidural collection.
• Epidural haematoma, metastatic cord compression and lymphoma.
• Disc herniation, transverse myelitis and Guillain-Barre syndrome.
• Meningitis, aortic dissection, pyelonephritis and psoas abscess.

Emergency surgical decompression and antibiotics are the usual treatment. Delay beyond 24 to 36 hours after the onset of weakness reduces the chance of recovery.

Surgery (urgent, ideally within 12 to 24 hours of diagnosis when there is a neurological deficit).

• Laminectomy or laminotomy with evacuation of pus, debridement of infected tissue and irrigation; instrumented fusion when there is instability, vertebral destruction or kyphosis (posterior instrumentation is acceptable in infection after debridement).
• Image directed aspiration for culture where the collection is small and the patient has no deficit.
• Non-operative treatment is considered only for patients with no or minimal deficit, a small collection or phlegmon, a known organism, high surgical risk, or established complete paralysis for over 24 to 48 hours; it requires hourly neurological checks initially, MRI repetition if any decline, and immediate surgery for any deterioration. Failure of non-operative treatment occurs in 40 to 50% in some series, so it is reserved for selected patients.

Antimicrobial therapy. Start immediately after blood cultures (and before surgery if the patient is septic or has a deficit).

• Empirical treatment: vancomycin 15 to 20 mg/kg intravenously every 8 to 12 hours (adjust to trough 15 to 20 mg/L and creatinine) with ceftriaxone 2 g intravenously every 24 hours; with Pseudomonas risk (injection drug use, immunosuppression), use ceftazidime or cefepime 2 g intravenously every 8 hours instead of ceftriaxone.
• Methicillin susceptible Staphylococcus aureus: flucloxacillin 2 g intravenously every 4 to 6 hours (maximum 12 g daily) or cefazolin 2 g intravenously every 8 hours (maximum 6 g daily).
• Methicillin resistant Staphylococcus aureus: vancomycin 15 to 20 mg/kg intravenously every 8 to 12 hours (adjust to trough 15 to 20 mg/L and creatinine), or daptomycin 8 to 10 mg/kg intravenously once daily (check creatine kinase weekly; stop statins), or linezolid 600 mg orally or intravenously every 12 hours (limit to 2 to 4 weeks; monitor blood count weekly; avoid with serotonergic drugs).
• Streptococci: benzylpenicillin 2.4 g intravenously every 4 hours or ceftriaxone 2 g intravenously every 24 hours. Gram negative bacilli: ceftriaxone 2 g every 24 hours or ceftazidime 2 g every 8 hours, with ciprofloxacin 400 mg intravenously every 8 to 12 hours or 750 mg orally every 12 hours if susceptible; extended spectrum beta lactamase producers: meropenem 1 g intravenously every 8 hours.
• Duration: 6 to 8 weeks in total, usually 2 weeks of intravenous treatment followed by an oral agent with good bone penetration when the patient is stable and the organism is susceptible (ciprofloxacin, levofloxacin 750 mg once daily, co-trimoxazole 960 mg every 12 hours, clindamycin 600 mg every 6 to 8 hours, or linezolid); 8 weeks or more with vertebral osteomyelitis.
• Fluoroquinolones carry a risk of tendon rupture, QT prolongation and aortic aneurysm; avoid with corticosteroids and in older adults when alternatives exist.

Supportive care.

• Paracetamol 1 g orally every 6 hours (maximum 4 g daily); oral or intravenous morphine 5 to 10 mg every 4 hours as needed (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2); laxative.
• Glycaemic control (blood glucose 6 to 10 mmol/L); bed rest with log roll until stable; bowel and bladder care (catheter for retention); pressure care; nutrition.
• Enoxaparin 40 mg subcutaneously once daily from 24 to 48 hours after decompression once haemostasis is secure (20 mg at creatinine clearance under 30 mL/min), with mechanical prophylaxis until then.
• Stop anticoagulants or antiplatelets only when needed for surgery, with the prescribing team.
• Operative cefazolin is replaced by the treatment antibiotics; if the patient is on none, give a dose within 60 minutes before incision after cultures.

Monitoring. Neurological examination every 1 to 2 hours in the first 24 hours, then every 4 to 6 hours; CRP and ESR weekly (falling CRP signals response); full blood count, creatinine and liver function weekly; vancomycin or other drug levels; creatine kinase with daptomycin. Repeat MRI for clinical worsening or if CRP stays high after 2 to 4 weeks. Review at 6 weeks, 3, 6 and 12 months with radiographs for kyphosis.

Referral and escalation. Any adult with back pain and fever, or back pain with a risk factor and neurological symptoms, needs same day MRI and spinal surgical review. Emergency referral for any deficit, sepsis, or bowel or bladder change. Involve infectious disease, rehabilitation and addiction services.

Special groups.

• Injection drug users: Pseudomonas and MRSA cover, endocarditis screen, opioid substitution and addiction support.
• Post-procedure abscess (epidural catheter, injection, surgery): remove the catheter or implant and send tips for culture.
• Older adults and renal impairment: adjust drug doses to renal function; higher mortality.
• Pregnancy: use beta lactams; avoid fluoroquinolones, tetracyclines and aminoglycosides; MRI without gadolinium.