Percutaneous electrical nerve stimulation in post-mastectomy neuropathic pain: A case report

Introduction

Globally, breast cancer is the most common cancer diagnosed in females, with a five-year survival rate of up to 90%.^1,2 Post-oncological treatment pain is a common side effect experienced by breast cancer survivors, with a prevalence of 25–60%. ³ In addition to pain, up to 50% of women experience other moderate to extreme upper body symptoms, including a restricted range of motion, sensation changes and weakness. Such symptoms have been reported up to 18 months after surgery. ⁴

Post-oncological treatment pain is often chronic, and its management is complex as the cause is multifactorial. Disease progression, chemotherapy, psychological factors and tissue trauma due to surgery and/or radiotherapy can all cause pain.^5,6 Chronic pain is often debilitating and may significantly limit the quality of life. ⁷

Transcutaneous electrical nerve stimulation (TENS) has been supported in the literature to treat pain. ⁸ TENS is a form of peripheral neuromodulation which transcutaneously stimulates nerves that are thought to be the pathological driver of the patient’s pain. Percutaneous electrical nerve stimulation (PENS) is an extension of TENS wherein specific nerves are targeted and directly stimulated percutaneously. Stimulation is typically performed proximal to the region of pain to affect the distal nerve distribution.

PENS has been utilised to treat various chronic conditions, including post-amputation pain, ⁹ post-electroconvulsive therapy headaches ¹⁰ and musculoskeletal pain. ¹¹ However, there are limited studies on using PENS in chronic post-mastectomy pain. ¹²

We report the use of PENS for treating chronic neuropathic pain following mastectomy and radiotherapy for breast cancer. The patient provided full written consent for her case report to be published.

Case report

A 55-year-old Caucasian female weighing 50 kg was referred to the North Queensland Persistent Pain Management Service (NQPPMS) for chronic left-sided anterior chest wall and axilla pain. The pain had been present for 14 months and followed bilateral mastectomy with axillary lymph node dissection for left-sided T1cN0M0 triple-negative breast cancer. The onset of pain was first experienced four to five days after surgery. She reported lateral chest wall pain involving her axilla on the left side. The pain was described as ‘pulling, burning, and tightening, with electric shock-like sensation’. This was initially managed as acute postsurgical pain with oxycodone and paracetamol.

She received four cycles of adjuvant chemotherapy and radiotherapy in the subsequent five months. This led to a significant radiation burn on her left lateral chest wall, cording (also known as axillary web syndrome, a hardened lymph vessel that feels like a tight cord) in her axilla, and a decreased range of motion (ROM) of her left arm. Over the next few months (eight months after surgery), with a physiotherapy regime including exercise, massage, stretching and swimming, the impact of her cording was reduced, and she regained full ROM in her arm. She also reported some pain resolution. She was then discharged from the physiotherapy service.

However, she re-presented 12 months after surgery with left-sided chest wall pain recurrence. Computed tomography imaging and ultrasound were unremarkable, although she still demonstrated cording in her left axilla. After a further two months of physiotherapy without adequate pain resolution, she was referred to NQPPMS. At her initial consultation, she rated her pain severity at a constant 8/10 on a verbal numerical rating scale. Her pain was experienced along her left chest wall and arm down to her elbow. She reported symptoms consistent with hyperalgesia and allodynia in the affected regions and denied paraesthesia. The examination was unremarkable, and her only analgesic medication was paracetamol.

Numerous anti-neuropathic medications and adjuvant therapies, such as pregabalin, amitriptyline and topical lidocaine patches, were tried but not tolerated. As part of the multidisciplinary pain management strategy that the NQPPMS provides, she also attended regular psychology consultations and continued physiotherapy massage and exercise with little improvement in her pain.

Forty-one months after surgery she had a trial of intercostal nerve blocks performed at levels T3 to T8 on the left side which did not provide significant pain relief. She was then given a five-day lidocaine infusion at 58 months. This had immediate partial relief with improved deep breathing but she still rated her pain as 3/10. The infusion, supplemented with regular paracetamol and transdermal lidocaine patches for breakthrough pain, allowed her to manage her pain well over the next four months. Another five-day lidocaine infusion was given at 67 months, reducing her pain score to a baseline of 6/10. However, the duration and degree of pain improvement decreased significantly with each lidocaine infusion. The patient was keen to pursue other treatment strategies as it was a 4-h commute from her home to the hospital for infusions.

A diagnostic left-sided serratus anterior plane block was performed at 87 months. This was performed under ultrasound guidance using 8 ml of 0.2% ropivacaine and 5.7 mg betamethasone. Her pain score was reduced from 8/10 to 4/10 with increased arm ROM and deeper breathing.

Given the success of the diagnostic serratus anterior plane block and following a detailed discussion with the patient, a left serratus fascial plane PENS procedure was undertaken. This was performed four months after her diagnostic block when her pain score had gradually returned 7/10. An Algotec NeuroStimulator PENS Therapy® device and a 22-gauge flexible probe with an 80 mm active length were used with Program C, which alternates between 100 Hz and 2 Hz every 3 s for 25 min.

The patient tolerated the PENS procedure well with no immediate complications. Over the next six months her pain score reduced to 3/10 from the previous 7/10 and she regained full ROM of her left arm. Repeat serratus plane PENS was performed about 16 months later, and she continues to report good pain relief.

Discussion

We report the use of PENS to treat post-mastectomy and post-radiotherapy chronic pain that was not responsive to traditional pain management treatments. The patient had experienced chronic pain and limited range of motion in her left arm for more than seven years. Various treatment modalities were trialled for her pain, with most providing little relief.

Pain is commonly classified into nociceptive, neuropathic, and nociplastic. Nociceptive pain arises from actual or threatened damage to non-neural tissue due to the activation of nociceptors transducing signals through nerve fibres. A lesion or disease of the somatosensory nervous system causes neuropathic pain. ¹³ Nociplastic pain arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain. The mechanisms are not entirely understood, but it is theorised that augmented central nervous system pain, sensory processing and altered pain modulation play important roles in nociplastic pain. ¹⁴

Neuropathic pain is most prevalent in cancer survivors, but a mixed type of pain is also prevalent and is more challenging to treat than pain from a single mechanism. ¹⁵ While the patient did have cording, which may contribute to nociceptive pain, ¹⁶ her pain was described using neuropathic descriptors as ‘burning and tightening, with an electric shock-like sensation’. Her pain was associated with the accompanying sensory signs of hyperalgesia and allodynia over a dermatomal area corresponding to the T3 to T8 levels on the left anterior chest wall. Therefore, at the time of presentation to NQPPMS, with this description and distribution of pain and history suggestive of a lesion of the somatosensory system, a diagnosis of probable neuropathic pain was made based on previously established diagnostic criteria. ¹⁷ It is noted that the patient’s pain could later have been classified as nociplastic pain based on the chronicity, regionality and evoked pain hypersensitivity. ¹⁸

Chronic post-mastectomy pain has been linked to several risk factors, including axillary lymph node dissection, cording, radiotherapy, being of an ethnic minority, being under 35 years old, with a prior history of chronic pain, diagnosis of depression or anxiety, advanced tumour stage, and catastrophising. ² Considering these, our patient was identified to have axillary lymph node dissection, radiotherapy and cording as risk factors for developing post-mastectomy pain syndrome (PMPS).

The serratus anterior plane (SAP) block was first documented by Blanco et al. in 2013. ¹⁹ This technique was proposed as a viable alternative to thoracic paravertebral and central neuraxial blockade for chest wall and upper abdominal incisions. ²⁰ Most reports of SAP blocks in the literature focus on chest wall analgesia in the acute setting, as the block is easy to perform and relatively safe.

PENS has proven highly effective in treating this patient’s chronic pain. Her pain score reduced to 3/10 and her ROM increased, allowing a significant improvement in function and quality of life.

With the advent of this technology, there has been extensive literature published on the use of PENS in the context of other types of chronic pain.^{9 –11} Still, there is limited literature on the setting of chronic post-mastectomy pain. PENS is a minimally invasive neuromodulation technique which acts at the subcutaneous level and is effective for certain types of chronic pain. It has been demonstrated that both PENS and TENS modulate Aβ nerve fibres ²¹ and the local release of biochemical mediators such as endorphins and neurotransmitters.^{22 –24} During PENS, a needle probe of varying length (area dependent) is inserted into the skin. The probe is tunnelled percutaneously along the axis of the painful area, typically within the subcutaneous tissue at a depth between 0.5 cm and 3.0 cm, and then activated. ²⁵ In this case, Program C of the Algotec NeuroStimulator PENS Therapy® device was used. This is a standard stimulation protocol based on published evidence for an increased release of enkephalins, beta-endorphin and endomorphin with 2-Hz stimulation, and of dynorphin at 100-Hz stimulation.^22,24,26

Some recent studies describe nerve blocks or radiofrequency neurolysis as a treatment for PMPS. One retrospective study investigated the use of thoracic paravertebral blocks to treat PMPS and reported immediate but short-term (less than one month) pain relief in 88% of patients. ²⁷ Another study described significantly decreased pain over six months in a case series of 100 patients who underwent pulsed radiofrequency and steroid injection targeting T2 and T3 dorsal root ganglia for intercostobrachial neuralgia after mastectomy. ²⁸

We propose that PENS may represent a safe and effective treatment for PMPS. As the relevant literature is promising but limited, further case reports and studies documenting the use of PENS are warranted in post-mastectomy patients where other treatments have failed to provide long-term benefits.