Adult patient one month post‑lumbar spine surgery presents with low‑grade fever (37.6 °C), new lower abdominal and coccygeal pain, normal exam otherwise—what is the appropriate evaluation and management?

Evaluation and Management of Post-Lumbar Surgery Fever with Lower Abdominal and Coccygeal Pain

This patient requires urgent MRI of the entire spine with contrast to rule out postoperative spinal infection (discitis, osteomyelitis, or epidural abscess), along with immediate laboratory workup including ESR, CRP, complete blood count, and blood cultures. 1

Immediate Diagnostic Priorities

High-Risk Clinical Context

• Postoperative spinal infection must be excluded first given the combination of fever (even low-grade at 37.6°C), new pain in anatomically relevant locations (lower abdomen and coccyx/sacrum), and recent lumbar surgery. 1
• Diagnostic delay in spine infection is common because symptoms are often nonspecific (back pain, fever) and indolent in presentation, but delayed diagnosis significantly increases morbidity and mortality. 1
• The one-month postoperative timeframe places this patient in the critical window for deep surgical site infection, which occurs in approximately 0.9% of posterior lumbar surgeries. 2

Imaging Strategy

• Contrast-enhanced MRI of the lumbar spine (minimum) is mandatory, as it is the gold standard for detecting postoperative spine infection, showing vertebral endplate involvement, disc space infection, epidural abscess, and paraspinal soft tissue involvement. 1
• Consider whole-spine MRI if initial lumbar imaging shows infection, as multilevel involvement occurs in 51% of spinal infections, with skip lesions in 8% of cases. 1, 3
• MRI can demonstrate epidural abscess, which has increased in incidence to 2.5-3 per 10,000 patients and is associated with significant neurologic morbidity when diagnosis is delayed. 1
• CT is valuable if MRI is contraindicated, for guiding biopsy, or assessing spinal stability, but MRI remains superior for soft tissue and neural element evaluation. 1

Laboratory Evaluation

• ESR and CRP are more reliable than white blood cell count for detecting spinal infection; WBC may be normal in up to 40% of cases. 3
• CRP >100 mg/L strongly suggests active spinal infection and rises rapidly with infection. 3
• ESR is highly sensitive for spinal infection and should be obtained. 3
• Blood cultures must be drawn before any antibiotics are started, ideally two sets from different sites. 1

Differential Diagnosis Considerations

Postoperative Spine Infection

• Deep surgical site infection after posterior lumbar surgery has independent risk factors including male gender, operating time ≥3 hours, preoperative steroid use, and trauma cases. 2
• Sustained fever (defined as fever appearing after postoperative day 3) occurs in 11.4% of spinal instrumentation cases, with 13.2% of these patients having surgical site infection versus 0.9% without sustained fever. 4
• Continuous fever pattern, increasing or stationary inflammatory markers, and CRP >4 mg/dL on postoperative days 7-10 are diagnostic clues for surgical site infection. 4

Nonpathologic Postoperative Fever

• Delayed postoperative fever (appearing after day 3) without infection occurs commonly after spinal surgery, with risk factors including posterior approach with anterior body work, trauma/tumor surgery, and long operative time. 5
• However, infection must be ruled out before attributing fever to nonpathologic causes. 5, 4

Drug-Induced Fever

• Cefazolin and other beta-lactam prophylactic antibiotics can cause postoperative fever, typically with mean onset 21 days (median 8 days) after initiation, though it can occur within days. 6, 7
• Drug fever should be considered only after infectious workup is negative and typically requires medication discontinuation for diagnosis. 6
• Fever from drug causes persists 1-7 days after stopping the offending agent. 6

Intra-Abdominal or Pelvic Pathology

• The combination of lower abdominal pain and fever warrants consideration of intra-abdominal sources, though the coccygeal pain strongly suggests spinal origin. 1
• If abdominal symptoms persist and spinal imaging is negative, abdominal CT should be performed per critical care guidelines for postoperative fever evaluation. 1

Management Algorithm

Step 1: Immediate Actions (Within Hours)

• Draw blood cultures (two sets from different sites) before any antibiotics. 1
• Obtain ESR, CRP, complete blood count with differential. 1, 3
• Order urgent contrast-enhanced MRI of at least the lumbar spine, extending to whole spine if any abnormality detected. 1, 3
• Examine the surgical wound carefully for erythema, warmth, drainage, or dehiscence. 1

Step 2: If MRI Shows Spinal Infection

• Perform image-guided aspiration biopsy before starting antibiotics (unless neurologic compromise is present) to obtain specimens for aerobic culture, mycobacterial culture and stain, and PCR for M. tuberculosis. 1, 3
• Withholding antibiotics for 1-2 weeks prior to biopsy improves diagnostic yield when neurologic status permits. 3
• If neurologic compromise or spinal cord compression is present, start empirical broad-spectrum antibiotics immediately after cultures and proceed urgently to surgical consultation. 1

Step 3: If MRI Is Negative for Spinal Infection

• Reassess for intra-abdominal pathology with abdominal/pelvic CT if lower abdominal pain persists. 1
• Review all medications started within the past 3-4 weeks for possible drug-induced fever, particularly beta-lactam antibiotics. 6
• Consider urinary tract infection if urinary catheter was used perioperatively; obtain urinalysis and culture. 1
• Monitor inflammatory markers (CRP, ESR) serially; rising or persistently elevated values suggest occult infection requiring further investigation. 4

Step 4: Empirical Antibiotic Therapy

• Do not start empirical antibiotics unless:
  • MRI demonstrates spinal infection with neurologic compromise (start after blood cultures drawn). 1
  • Patient develops hemodynamic instability, severe sepsis, or altered mental status. 6
  • Biopsy cannot be performed and clinical suspicion for infection is very high. 1
• If empirical therapy is required before biopsy, use vancomycin plus a third- or fourth-generation cephalosporin to cover Staphylococcus aureus (including MRSA) and gram-negative organisms, the most common postoperative spine pathogens. 1

Critical Pitfalls to Avoid

• Do not attribute fever to "normal postoperative course" or atelectasis without thorough investigation in a patient one month post-surgery with new pain symptoms; atelectasis should be a diagnosis of exclusion. 1, 6
• Do not start antibiotics before obtaining blood cultures and ideally before tissue biopsy, as this significantly reduces diagnostic yield. 1, 3
• Do not rely on normal white blood cell count to exclude infection; ESR and CRP are more sensitive. 3
• Do not perform lumbar puncture unless there are specific CNS symptoms (severe headache, altered mental status, focal neurologic deficits beyond expected postoperative changes), as the concern here is vertebral/epidural infection, not meningitis. 8
• Do not delay imaging while waiting for inflammatory markers to rise further; MRI should be performed urgently given the clinical presentation. 1

When to Escalate Immediately

• Any new or progressive neurologic deficit (weakness, numbness, bowel/bladder dysfunction) requires emergency neurosurgical consultation. 1
• Hemodynamic instability, severe sepsis, or altered mental status mandates ICU-level care and immediate empirical antibiotics after cultures. 6
• MRI showing epidural abscess or spinal cord compression requires emergency surgical evaluation. 1