Peripheral Nerve Stimulation for the Management of Pediatric Neuropathic Pain Free

A 15-year-old adolescent male presented to the pain clinic for management of chronic left thigh and knee pain. He had no significant medical history. The pain started 2 years after he was involved in a motor vehicle accident, during which he sustained impact to the lateral aspect of his left knee while riding his bike. He initially presented to an emergency department for evaluation; radiographs were unremarkable. He continued to have pain and followed up with an orthopedic surgeon who ordered magnetic resonance imaging. Imaging showed possible edema around the tibial tubercle; there were no other overt signs of injury. No surgical treatment was offered, and he was referred to our pain clinic. His pain at the time of presentation was in the anterior thigh with radiation to the anteromedial aspect of the left knee. The pain persisted despite conservative therapies that included 6 months of physical therapy, mobility exercises, and the constant use of a sleeve/brace. Additionally, he was taking 1 to 2 ibuprofen tablets daily. These therapies did not decrease the pain or improve the functionality of the limb. He described the pain as constant, sharp, and throbbing. He also reported numbness and tingling in the anterior thigh and medial part of the knee. His pain intensity at presentation, using the Numerical Rating Scale, was 4/10 at rest that increased to 8/10 with activity. His pain limited him from walking more than 20 feet. He did not report any alleviating factors and denied any additional associated symptoms including bowel or bladder changes, saddle anesthesia, recent fever/chills, and weight loss.

The LEEDS assessment of neuropathic symptoms and signs pain scale was performed in the clinic¹¹  (Table 1).

On physical examination, we identified no swelling, ecchymosis, or deformity over the left knee and thigh, but noted tenderness along the mid-third of the tibial crest and diffusely over the medial and anterior aspects of the knee. We detected no tenderness over the fibular head or the medial and lateral joint lines of the knee. He demonstrated full active range of motion with knee flexion and extension without eliciting his typical pain. There was increased pain with tapping over the saphenous nerve at the mid-thigh. Strength testing was 5 of 5 for knee flexion and extension bilaterally. Sensation was intact to light touch throughout the left lower extremity. Further sensory testing was as described in the LEEDs questionnaire. Physical examinations also included performance of McMurray test, Lachman test, valgus/varus stress tests, and anteroposterior drawer tests, all of which were negative.

The patient then underwent a saphenous nerve block with steroids (10 mg dexamethasone and 5 mL 0.25% bupivacaine), which provided 2 weeks of 100% pain relief. Using ultrasound guidance, a peripheral nerve stimulator (SPRINT, SPR Therapeutics, Inc., Cleveland, OH) was subsequently implanted on the left saphenous nerve for 60 days (Fig 1–4). The patient tolerated the procedure well and was given instructions to cover the lead exit site with a plastic dressing when showering to minimize accidental lead dislodgement. At his 2-month follow-up, the PNS leads were removed. He reported significant pain relief and functional improvement at that time. Specifically, he described being able to participate in family activities, ride his bike, and run with friends, all of which were hindered before initiation of PNS. His updated Numerical Rating Scale (NRS) pain score had fallen to 1/10 at rest and 3-4/10 with activity. The pediatric pain disability index was then performed^12,13  (Table 2).

He had a follow-up visit 1 year after initiation of PNS. His pain score continued to be 1-2/10 at rest and 3/10 with activity. He was able to return to physical activity including running, biking, and attending gym classes; running beyond 30 minutes and squatting caused mild discomfort but was tolerable. In addition, he took up wrestling 5 months after the procedure. He discontinued the use of ibuprofen and reported no complications from PNS.

Our case report presents the successful management of a pediatric patient with peripheral neuropathy with neuromodulation/PNS. Pediatric chronic pain provides significant challenges to physicians for both diagnosis and treatment. In addition, patient communication barriers and psychosocial factors of a family dynamic dealing with their child in pain can further complicate this process.

The assessment and diagnosis of neuropathic pain in children are often based on the design and guidelines created for adults. No specific pediatric guidelines are available.¹⁴  Diagnosis of neuropathic pain is based on history and clinical examination; specific laboratory tests are unavailable; therefore, very young children who may have difficulty with verbalization make this diagnosis a challenge. However, evaluations should include character; intensity; temporal aspects of pain including frequency, aggravating, and relieving factors; and response to treatment in conjunction with a thorough physical examination to delineate specific nerve injury. Screening questionnaire tools, such as LEEDS assessment of neuropathic symptoms and signs and Neuropathic Pain Questionnaire, are also useful in the diagnosis of neuropathic pain.^11,15  The additive effect of frequent steroid injections for pediatric peripheral nerve injury has not been studied. In our patient, a repeat saphenous nerve block would not have provided additional benefit. The initial block provided significant short-term relief, so further diagnostic information was not necessary. A small amount of steroid is added in the block in anticipation of long-lasting pain relief, but the extended relief period was only 2 weeks in duration and therefore was also not a reasonable therapeutic option. Electroneuromyography, skin biopsy, and neuroimaging modalities may help in acute injury but if the diagnosis is highly probable with history and examination, these modalities are rarely required for clinical decision-making in pediatric chronic pain.¹⁶ 

Pain management physicians prefer a multimodal treatment approach for pediatric neuropathic pain using a combination of physical therapy, oral medications, and in rare conditions local anesthetic/steroid blocks.¹⁷  Oral medications including anti-inflammatories, muscle relaxants, antidepressants, anticonvulsants, and opioids may help in initial management. Drug therapy is often unsatisfactory because the underlying mechanism in the pediatric population is rarely well understood. PNS involves the application of electrical stimulation via stimulating electrodes placed near the affected peripheral nerves. Studies have demonstrated that the PNS system acts via both peripheral and central analgesic mechanisms and has a role in modulating the autonomic nervous system.¹⁸  PNS was initially thought to provide an analgesic effect based on the gate-control theory where the electrode stimulates the A-β nerve fibers preferentially, which induces an inhibitory response on the transmission of a signal from pain processing A-δ and C nerve fibers.¹⁹  Recent studies have also shown its involvement in modulating the signals in cortical and subcortical areas of the brain.^20,21  Neuroinflammatory marker modulation has also been reported, including decreases in proinflammatory cytokines interleukin-1β, interleukin-6, and tumor necrosis factor-α after initiation of PNS.²² 

PNS is a minimally invasive treatment of pain that can be initiated and monitored in an outpatient setting. It does not involve medication and therefore potential harmful interactions with other medications are limited. PNS can also be used in combination with physical therapy, psychological support, and medication management, making it a versatile treatment option. There are rare limitations to using PNS. However, implantation of the PNS device has potential risks of infection, bleeding, lead breakage, and incomplete coverage. The duration of the PNS device placement can vary depending on the needs of the patient. It can range from 60 days (as was done with the SPRINT PNS used in our case) to a more permanent implant. We were not able to identify previous published reports of treating pediatric neuropathic pain with PNS; hence, our case provides new information for pediatricians and pain specialists about this subject matter.

In conclusion, PNS is a promising treatment option for pediatric neuropathic pain. However, PNS is not suitable for every child, and the decision to use this treatment should be based on a comprehensive evaluation of the child’s pain levels and response to other treatments. PNS typically should be well tolerated by adolescent children, and the device can be easily removed if the child experiences any adverse reactions. Cognitively delayed children may not have the ability to describe their neuropathic pain or adequately report any adverse effects of nerve stimulation treatment. Young children may not be able to adequately handle and care for the device. Therefore, PNS is not recommended for developmentally/cognitively delayed children and children younger than 10 years of age. Further research is needed to understand the long-term effects of PNS and its applicability in the pediatric population younger than age 10 years. Our case study shows its effectiveness in reducing pain and disability, improving function, and enhancing the quality of life in an adolescent child suffering from neuropathic pain.

PNS

peripheral nerve stimulation