Ultrasonography in Pain Medicine SIG

Neuraxial Hardware Infection: A Problem-Based Learning Discussion

May 24, 2021

Zachary Ashmore, MD; Stephen Covington, MD; Rajat Moman, MD; Markus Bendel, MD

A 64-year-old woman with a past medical history of type 2 diabetes mellitus (HgbA1C: 7.4) and hypertension was deemed to be a candidate for a percutaneous spinal cord stimulator (SCS) trial for Failed Back Surgery Syndrome. She had excellent results in the trial period which lasted 10 days and is now two weeks post-op from implantation. She calls your clinic with concerns of itching and redness around the site of the implanted battery. She presents to clinic with the following vitals: heart rate 80, blood pressure 130/84, respiratory rate 16, temperature 36.3 Celsius. Physical exam reveals the implanted pulse generator (IPG) incision site is erythematous, warm to the touch, and the erythematous region is tender to palpation (Figure 1). The patient denies systemic symptoms like fevers or chills, denies purulent drainage, and is ambulating well on her own.  

Figure 1. Post-operative examination of implanted pulse generator.

 

1. Based on the available information, how would you classify this infection?


a. Superficial surgical site infection (SSI)

b. Deep, uncomplicated SSI
c. Deep, complicated SSI

This patient’s clinical presentation is most consistent with a superficial surgical site infection (SSI). The Neurostimulation Appropriateness Consensus Committee (NACC) Recommendations for Infection Prevention and Management states that superficial SSIs are more common than deep SSIs. While superficial SSIs most commonly occur in the first 30 days after implantation (as seen in this case), deep SSIs can occur up to one year after implantation.

2. What diagnostic testing do you order at this point?


a. Complete blood count (CBC)
b. Magnetic resonance imaging (MRI)c. Ultrasoundd. Blood cultures

In this case, CBC, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are good first line considerations for this patient given clinical picture of superficial SSI. However, these labs are not very sensitive or specific for infection, and treatment for superficial infection may be pursued without laboratory abnormalities. If all labs are abnormal, suspicion for deep or severe infection should be increased. It should also be noted that inflammatory markers such as ESR and CRP may be elevated from the procedure itself. Blood cultures may be considered. Imaging is not warranted at this time.

3. What factor(s) may predispose her to a possible surgical site infection?

a. Type 2 Diabetes Mellitus
b. Duration of trial period
c. Hypertension
d. Diagnosis of Failed Back Surgery Syndrome
e. Both a and b

    Longer surgical time and trial duration greater than 5 days have been shown to be risk factors for infection, and she has an extended trial period of 10 days. While not demonstrated as risk factors for SCS infection in the limited studies to date, commonly associated variables such as uncontrolled diabetes mellitus (DM) and smoking should raise caution for surgical site infection. Well controlled DM may also pose a small increased risk of infection. In practice, many use a HgbA1c cutoff of 8 before proceeding with implantation.

    4. Given reassuring labs, you decide to move forward with oral antibiotic therapy.  Which treatment regimen do you choose?

    a. First-generation cephalosporin for 7 days
    b. IV antibiotics with narrowed oral antibiotic after culture susceptibilities
    c. Consult infectious disease specialist
    d. Oral fluoroquinolone for 14 days

    A first-generation cephalosporin for 7-10 days is the antibiotic of choice for a superficial infection. This choice affords appropriate gram-positive coverage. Staphylococcus, streptococcus, and enterococcus species are most common. Methicillin-resistant staphylococcus aureus (MRSA) coverage can be considered based on colonization.

    5. In SCS associated infections, when is explant indicated?

    a. If the patient develops clinical instability after conservative care
    b. Explant is indicated with any deep infection
    c. In any infection, superficial or deep, if the patient has not received adequate clinical improvement in pain
    d. None of the above

    Explant is indicated for any deep infection.

    Redness and swelling of the surgical site initially improve with a 7-day course of oral antibiotics. However, one week later, she again has worsening redness, continued back pain along with a small amount of purulent drainage. During neurological assessment, manual muscle testing reveals 4/5 strength in the right hip flexors and quadriceps muscles with a diminished right patellar reflex. Heart rate is 85, blood pressure is 130/83, respiratory rate is 14, and temperature is 37.3.

    6. Besides repeat serum labs, what other laboratory testing do you request? 

    a. Serum cultures
    b. Cultures of purulent drainage
    c. Repeat serum labs including CBC, ESR, and CRP
    d. All of the above

    Epidural abscess vs deep infection is now at the top of your differential. Deep infection is suspected if dehiscence, purulent drainage, or erosion of device components is present. Epidural abscess is considered when there is ongoing/worsening back pain with neurological deficits. Common presenting clinical features of epidural abscess include back pain (66.8%), motor weakness (52.0%), fever (43.7%), sensory abnormalities (40.0%), and bowel/bladder incontinence (27.1%). The most common abscess location is the lumbar spine (48%). If epidural abscess is initially suspected, pre-explantation imaging is warranted. If only deep infection is initially suspected, pre-explantation imaging is not necessary, but it is good practice to obtain post-explantation advanced imaging to evaluate for complication such as epidural abscess or osteomyelitis.

    7. What imaging study would be indicated for further investigation of epidural abscess?

    a. Lumbar spine x-rays
    b. Computed tomography (CT) lumbar spine
    c. MRI lumbar spine with contrast 
    d. MRI lumbar spine without contrast

    Your patient now has back pain with neurological symptoms including weakness on examination. This raises concern for epidural abscess with neurological compression. Imaging study of choice is MRI with contrast for spinal infection.

    8. Imaging shows an epidural abscess at the L3-L4 level. What are your next steps in management?

    a. Neurosurgery consultation
    b. Diagnostic fine needle aspiration of the abscess
    c. Continued oral antibiotics for 6 weeks
    d. Infectious disease consultation
    e. a and d

    In the neurosurgical literature, the incidence of epidural abscesses of any etiology is currently estimated at 0.2 to 2 per 10,000 hospital admissions. Independent risk factors for epidural abscess include diabetes mellitus, end stage renal disease, spinal trauma, prior spinal surgery, immunocompromised state, IV drug use, and alcoholism. The most common organism cultured is Staph Aureus. In the general population, epidural abscess management typically involves 60% of cases undergoing a decompression and laminectomy while 40% can be managed with a 4 to 6-week course of IV antibiotics. However, in patients with SCS and an epidural abscess, surgical management is recommended. With only two reported cases of epidural abscesses occurring during SCS trials, this is a rare occurrence.

    9. The patient is seen in the pre-operative area immediately prior to planned laminectomy with incision and drainage of a known abscess. They are endorsing moderate-to-severe pain and diminishing effects of a short course of opioids they were prescribed in the setting of this complication. You discuss their care with their anesthesiologist who decides this patient will benefit from a multimodal perioperative pain management plan. Which of the following medications would be helpful adjuncts to consider?

    a. Ketamine
    b. Methadone
    c. Lidocaine

    All three options (a, b, and c) are reasonable to consider. Most of these medications have been studied in the setting of lumbosacral fusion and studies have both supported and refuted their use. Importantly, there is no research that studies our patient’s clinical situation. A recent RCT in patients chronically on opioids by Nielsen et al. revealed ketamine reduced daily oral morphine equivalents in the one-year period after fusion. Murphy et al. found reduced hydromorphone use on postoperative day 1-3 in patients randomized to intraoperative administration of methadone versus standard hydromorphone. De Winter et al. randomized patients to intraoperative lidocaine or placebo and found no difference in postoperative opioid consumptions, however, lidocaine is likely safe and could still be an additional adjunct in the appropriate context.

    10. If instead, there was no epidural abscess and the patient had a normal neurological examination (deep infection), after explanation of the SCS device, what antibiotic regimen do you pursue?

    a. Empiric gram negative antibiotic coverage followed by culture directed therapy for 7-10 days
    b. Consultation with infectious disease specialist
    c. Empiric gram positive antibiotic coverage followed by culture directed therapy for 21 days
    d. Empiric gram positive antibiotic coverage followed by culture directed therapy for 7-10 days

    Empiric coverage is generally necessary for gram positive species only. This may be directed by local antibiogram. Treatment should then be narrowed based on serum and intra-operative culture data. Consultation with an infectious disease specialist may be warranted with any complicated infection. After explantation, 7-10 days of therapy indicated (longer in the case of a complicated infection). In a clinically stable patient with uncomplicated deep infection, initiation of antibiotics may be deferred until after explanation and collection of operative cultures.

    11. What are preventative measures to reduce risk of infection?

    a. Pre-operative methicillin-susceptible staphylococcus aureus (MSSA)/MRSA screening and decolonization
    b. Intra-operative weight-based antibiotic dosing
    c. Post-operative occlusive dressing for 24-48 hours post-implantation
    d. All of the above

    There is a lack of specific evidence in SCS. Nonetheless, the broader surgical literature informs prudent preventative measures. Pre-operative measures include MSSA/MRSA screening and decolonization with 2% mupirocin twice daily for five days, and using electric clippers used for hair removal. Intra-operative measures include weight based antibiotic dosing: 1g Cefazolin for <80kg; 2g Cefazolin for 81-160kg. Post-operative measures include utilizing an occlusive dressing for 24-48 hours post-implantation.

    12. Your patient returns to the clinic after completion of her antibiotic course and resolution of her deep infection. Her pain has markedly increased since explantation and she asks if she can have another spinal cord stimulator implanted. How do you counsel her?

    a. Re-implantation may be considered in 12 weeks after discussion of risks and benefits, including the risk of future infection
    b. This patient is no longer a candidate for SCS placement
    c. Re-implantation may be considered in 1-2 years after discussion of risks and benefits, including the risk of future infection

    There are no consensus recommendations for a timeline of re-implantation.  Some experts recommend 12 weeks if the infection is resolved. Any consideration of re-implantation should be assessed in the context of estimating risk of future infection.



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