Epidural spread of surgical site infection from spinal cord stimulation trial

Abstract

We present a case of deep surgical site infection (SSI) at a spinal cord stimulator (SCS) trial implantation site, resulting from an allergic reaction to an unknown agent. A 38-year-old female with complex regional pain syndrome began an SCS trial, noting 100% pain relief for 5 days. Fluid drainage from the surgical site was reported on POD6 and trial leads were removed the following day. The patient was hospitalized with sepsis. Blood cultures revealed Staphylococcus aureus. MRIs showed skin breakdown and cellulitis of the paraspinal musculature extending into the epidural space. The patient was maintained with antibiotics and rigorous wound care for 9 days and the surgical site infection resolved. The patient proceeded to SCS implantation, and reported good pain relief with the implanted device.

Plain Language Summary

This case report describes the treatment of an infection developed during a spinal cord stimulator (SCS) trial period. SCS are medical devices used to treat pain, they work by applying electrical current to the areas of the spinal cord that cause patients’ pain. Before patients get an SCS device implanted, they often undergo a trial period first. During a trial, the stimulator device stays outside the body, and only the wires carrying electricity to the spinal cord are implanted. Typically, SCS trial and implantation procedures are safe and result in effective pain relief. However, infections are a dangerous potential complication that can result from these procedures. In our case, the patient developed an infection during an SCS trial period, likely resulting from an allergic reaction to their surgical dressings. The infection traveled down the wires and nearly reached the spinal cord. Since the infection was quickly identified and managed, devastating complications were avoided. The patient was able to get a permanent SCS after the infection was resolved, and had effective pain relief. Our report emphasizes the importance of using strict infection prevention techniques, and monitoring patients for signs of infection throughout SCS trials.

Plain language summary

Article highlights.

• We present a rare case of surgical site infection with epidural spread from a spinal cord stimulator trial, which was diagnosed swiftly by clinical examination, blood culture analysis and contrast-enhanced MRI.

• Oral and IV antibiotics, as well as rigorous wound care, helped resolve the infection before epidural abscess, meningitis or other further complications could develop.

• The infection stemmed from an allergic skin reaction to an unknown agent, though we speculate that it was caused by wound-closure adhesive or surgical dressings.

• The patient fully recovered and proceeded to spinal cord stimulator implantation, noting good pain relief with the implanted device.

• This case report emphasizes the importance of postoperative monitoring and timely infection management in the context of spinal cord stimulator trials.

1. Background

Surgical site infections (SSIs) represent nearly 22% of all healthcare-associated infections, leading to significant costs and patient morbidity [1,2]. SSIs can arise as a complication of procedures such as total joint replacements and the use of implanted medical devices such as spinal cord stimulators (SCS) and intrathecal drug delivery systems [3]. While using SCS to elicit long-term analgesia in intractable chronic pain patients is a safe and efficacious option for those indicated, it is not without risk of complications [4]. Many of the most common SCS related complications, such as lead migrations [5], pose no significant risk to patients’ overall health. However, SSIs that develop as a result of SCS treatment are a serious, potentially life-threatening risk [6,7]. Infection rates in SCS generally range from 2.45 to 6%, though rates as high as 10% have been reported [8,9]. While reported SCS related infection rates have decreased over the past decade [7,10], SSIs remain among the most challenging complications for SCS patients and providers.

The majority of SCS related SSIs are caused by pathogens originating in patients’ own skin flora, which infect internal tissues through surgical incisions [3]. In descending order, the most common causative organisms for SSI in interventional pain procedures are Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus, Escherichia coli and Pseudomonas aeruginosa [3,4]. The implantable pulse generator site, a pocket formed via an incision typically in the lower abdomen, is the chief location of over 50% of SCS related SSIs [4,9]. However, SCS trials, where the leads are introduced percutaneously but the generator remains external, come with a risk of SSI as well [6,11]. While rare compared with SSIs related to implanted SCS devices [5], SSIs stemming from SCS trials can generate serious complications such as epidural abscess formation [6,12] and bacterial meningitis [13]. Despite low complication rates overall and promising potential for pain relief, the SSI risk associated with SCS trials should not be understated. Here, we explore a case of unexpected bacterial introduction at the surgical site of an SCS trial, which resulted from an unknown allergic reaction. This SSI case triggered intensive, multidisciplinary management of a patient with a history of multiple illnesses. Where most published case reports of SCS related SSI focus on patients who developed epidural abscesses [6,12,14], our report describes a timely diagnosis and management that prevented such severe complications. This case report serves as an apt model of close postoperative monitoring, assessment and appropriate action taken to prevent further, more devastating complications in the context of an SCS trial-related SSI.

2. Case presentation

A 38-year-old female patient with a history of complex regional pain syndrome type 1 of the right lower extremity, diagnosed per the Budapest Clinical Diagnostic Criteria [15], was determined to be a candidate for SCS therapy and underwent a screening trial period. The patient had a history of allergic reactions to multiple agents, including adhesives and lanolin. Preoperative antibiotics were administered prior to trial lead implantation, and the procedure was uneventful. The StayFIX^® fixation device (Merit Medical, UT, USA) for percutaneous catheter securement, which is specifically designed to stop migration, movement and accidental removal of the catheter, was used to secure the trial leads to the skin. In addition, Tegaderm^® Transparent Film Dressing (3M^®, MN, USA) was used to secure the leads on top of the StayFIX. The patient had used Tegaderm multiple times in the past with no allergic reaction. Throughout the first 5 days of the trial, the patient reported 100% pain relief. On POD6, the patient noted clear fluid drainage from the dressing site but denied fever, chills, tachycardia, hypotension, pruritus, purulent drainage, wound dehiscence, swelling and pain or warmth over the surgical site. The patient was prescribed cephalexin (500 mg QID) and instructed to follow-up in the office on POD7. Upon arrival, the patient had a fever of 101.3°F and new redness and pain upon palpation over the SCS trial site. Clear fluid drainage around the trial leads was noted, and the leads were removed. Entry sites were swabbed during the lead extraction, and sent to the hospital microbiology laboratory for culture to check for local bacterial infection. The tips of the leads were sent as well. However, the laboratory canceled these samples due to the high risk of contamination from skin flora and the potential for false positive responses. Blood tests were obtained, including a basic metabolic panel, complete blood count (peak white blood cell count 18.3 cells/ml), C-reactive protein (CRP; peak 22.4 mg/l), erythrocyte sedimentation rate and blood cultures. A consultation with an infectious disease specialist was obtained. The patient was urgently admitted to the hospital on the same day.

The patient became lethargic and hypotensive within an hour of hospital admission, complaining of headache, neck stiffness and increased back pain. Broad-spectrum antibiotics vancomycin and cefepime were prescribed. The patient was transferred to the ICU with an early sepsis diagnosis, and supportive therapy was initiated. After a day in the ICU, the patient was considered stable and transferred to a regular medical ward (POD8). Blood culture analyses revealed S. aureus, Acinetobacter baumannii and Acinetobacter haemolyticus.

Thoracic and lumbar MRIs were obtained on POD8. MRI findings were consistent with local skin breakdown due to allergic reactions and the introduction of skin flora to the lead implantation sites. Cellulitis of the dorsal thoracolumbar paraspinal musculature was observed, extending into the epidural space (Figure 1). MRIs of the thoracic and lumbar spine enhanced with IV gadolinium-based contrast media (GBCM) demonstrated bacterial infiltration of the dorsal epidural space as well as discrete small rim-enhancing collection extending from T11-L1 (POD8). MRIs using STIR to suppress radiographic signal from fat revealed hyperintense infiltration and enhancement of the dorsal thoracolumbar paraspinal musculature, with no discrete drainable fluid collection. Enhancement of dorsal thoracolumbar subcutaneous tissues was observed as well. Signal intensity was normal within the spinal cord, and imaging revealed no abnormal intrathecal enhancement. The patient was managed in the hospital with an antibiotic regimen and supportive therapies, including daily wound care.

Figure 1.

Lumbar MRIs with gadolinium contrast showing surgical site infection spread. (A) Axial T1w image of L1 level. (B) Sagittal T1w image of lumbar and sacral spine. Arrows indicate contrast enhancement in subcutaneous tissues, paraspinal muscles and the epidural space.

Spinal surgery and neurology consultations were obtained. The patient was determined not to be a candidate for further surgery, as no spinal cord compression or localized collection such as epidural abscess was observed. The clinical scenario improved with the patient responding well to IV antibiotic therapy and daily wound care. A repeat MRI with IV GBCM on POD14 demonstrated improved subcutaneous edema and reduced signal enhancement of the dorsal thoracolumbar region. No MRI signal abnormality was detected in the thoracic spinal cord nor the cauda equina nerve roots, and no new drainable collection was present. There was no evidence of intrathecal enhancement or spinal cord compression. The patient was discharged home after 9 total days of hospitalization (POD16), with a prescription for cephalexin (100 mg PO Q8H, 7 days). The patient noted improvements over the following 6 weeks, resulting in complete resolution of their headaches, neck stiffness, back pain and skin lesions.

After clearance by infectious disease and dermatology, the patient proceeded to permanent SCS implantation approximately 6 months after the SCS trial. The patient developed another allergic skin reaction postoperatively, possibly to a different low-allergenic surgical dressing postoperatively (Medipore^® +Pad Soft Cloth Adhesive Wound Dressing, 3M^®, USA), though without any SSI development. This second reaction was managed promptly with IV steroids after consultation with dermatology and infectious disease specialists. The allergic skin reaction was resolved without incident, and the patient reported effective pain relief from the implanted SCS device.

3. Discussion

The majority of SCS related SSIs occur at the implantable pulse generator implantation site, while infections at lumbar incision and electrode implantation sites occur at lower rates [4,9]. Our SSI case represents a rare complication from an SCS trial, though the infection was caused by the most common bacteria in SCS related SSIs (S. aureus) [7], and the patient was managed using stereotyped techniques [9,16].

Superficial SSIs in SCS involve the skin and subcutaneous tissue surrounding the incision or implantation site; these infections usually occur postoperatively within 30 days. Conversely, deep SSIs involve tissues such as muscle, fascia, epidural space, vertebrae and meninges, and may occur up to 1 year postoperatively [16]. Deep SSIs are reported less frequently than superficial SSIs; they are more severe, and may have a more insidious onset [17]. In our case, the onset of deep SSI symptoms was within 1 week, as a result of rapid skin breakdown at the electrode entry site due to allergic reaction.

The patient in our case had a history of multiple allergies, including adhesives and lanolin. Surgical sterilization solutions, surgical dressings and wound closure adhesive (Dermabond^®, 2-Octyl cyanoacrylate) may be responsible for allergic skin reactions in the context of SCS trials [18]. It is unlikely that the patient is allergic to SCS materials, as the patient did well following IV steroid treatment of their second allergic reaction, despite the SCS remaining implanted. In some cases of allergic reaction to SCS related materials, specific allergens can be identified through epicutaneous patch testing, which can allow for reimplantation if said allergen is an interchangeable material [19]. In our case, patch testing was not utilized, leaving the origins of the patients reaction unknown. If the allergy test was performed for possible adhesives and the dressings prior to the trial and implantation, the risk of allergic reaction could have been reduced.

Distinguishing infection from contact dermatitis is critical, as this determination can have a critical influence on treatment decisions. While the patient showed signs of allergic contact dermatitis, their condition was treated primarily as an infection, with a typical antibiotic and wound cleaning regimen appropriate for deep SSIs of mild-moderate severity [20–22]. The expeditious removal of offending agents is necessary for resolving dermatitis symptoms, which, in our case, were likely caused by the adhesive and dressings used following the SCS trial and implantation [23,24].

Monitoring the symptoms and signs of a systemic infection, such as fever, lethargy, mental status changes and fatigue, is extremely important, as the infection can proceed to systemic infection such as sepsis. Early infectious disease consultation, obtaining appropriate cultures and admission to the hospital for close monitoring are also important. In our case, the patient progressed rapidly from a local infection to meet the criteria of early sepsis, requiring a transfer to the ICU for supportive therapy. Early diagnostic workup, such as an MRI study with GBCM, is important to evaluate the extent of the infection. Neurological monitoring, as well as neurology and spinal surgery consultations, are necessary to decide the most appropriate therapy for the patient. Monitoring the CRP levels in the blood is critical for timely SSI diagnosis. Failure of CRP levels to normalize postoperatively, or an acute increase in CRP levels, is a sensitive and reliable predictor of SSI [25]. Empiric antibiotics should be promptly initiated when an SSI is suspected, and narrowed antibiotic coverage should be employed once microbial cultures have determined the causative organism(s) [20,26].

Additionally, an infectious disease consult should be obtained when SSI is suspected, and neuraxial MRI with IV contrast should be utilized, given the potential tract from the skin to the epidural space [12,16]. While superficial SCS related SSIs may be managed conservatively with antibiotics and close monitoring, deep SSIs usually warrant an explant of SCS materials [4]. Once the hardware is removed from an SSI and purulent material drained, copious irrigation is recommended for the purpose of clearing all infected material [26]. Considerations should also be made for drain placement and primary wound closure techniques versus serial packing [9].

It is noteworthy that SCS trial periods are controversial, as they are imperfect predictors of pain relief from permanent implants [27], and undergoing multiple procedures inherently increases patients’ risk of developing complications such as SSI. SCS trials have been associated with significant patient morbidity and even death [28]. However, the incidence of SSIs in relation to SCS trial and implantation can be minimized through a number of methods. Preoperative antibiotics are recommended as a preventative [9,21], though their use had little effect in our case. Hair removal at SCS surgical sites is known to increase SSI rates and should be avoided when possible [22]. Additionally, prolonged SCS trials (median 21 days) are associated with a significantly higher SSI incidence rate than shorter trials (median 6 days) [11]; the SCS trial in our case was near the upper limit of advisable duration. Recent data also demonstrates that using absorbable polymer antibacterial envelopes surrounding implanted SCS device components can significantly reduce SSI rates [29]; this practice may become a mainstay SSI preventative in the future. Importantly, two recent studies identified low compliance rates with infection prevention guidelines created by the Neuromodulation Appropriateness Consensus Committee [21], US Centers for Disease Control and Prevention, UK National Institute for Health and Care Excellence, and Surgical Care Improvement Project [22] among large samples of physicians. All physicians implanting or monitoring these devices should have a strong knowledge of relevant infection prevention and management guidelines [9].

4. Conclusion

SCS related SSIs are complications that can cause significant patient morbidity, even during trials. This case demonstrates that infections may still occur when preventative techniques are utilized, and physicians’ recognition of SSI signs and symptoms is paramount. Vigilance in identifying and treating SSIs in SCS is just as essential as the performance of trial and implantation procedures themselves.

Author contributions

This report was conceptualized by S Gungor and T Mukhdomi, who also oversaw treatment in the case described. S Gungor and T Mukhdomi developed the treatment plan (Methodology). T Mukhdomi prepared the original draft of this manuscript, which was reviewed and edited by S Gungor. B Andrassy conducted the literature review, created the figure and wrote the final version of the manuscript with critical revisions. S Gungor supervised the creation of the report. All authors read and approved the final manuscript.

Financial disclosure

The authors have no financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Competing interests disclosure

The authors have no competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Informed consent disclosure

Informed consent was obtained from the participant included in this report. All procedures involving human participants were performed in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments and comparable ethical standards. This report was approved by the Hospital for Special Surgery IRB (10/6/2022).