Usually, sciatic schwannomas are asymptomatic until they start to compress the sciatic nerve which leads to leg pain . The treatment is a complete resection of the tumor without causing any damage to neurological functions .
We report a case of a 50-year-old woman referred for treatment of persistent neuropathic pain in the left lower limb after resection of a schwannoma.
2 Case report
The patient’s history goes back to 1986 when she started to have electric-like pain in her lower left limb upon intercourse. She was 27 years old and had one child. She underwent physical examinations which revealed a palpable left ovarian cyst. Then, she had exploration laparatomy during which the cyst was removed. However, 2 days after the operation she had severe pain at rest on her lower left limb. The pain was burning and pricking in nature. She was not able to sleep on her left side. She was advised to consult a rheumatologist since the pain was not related to the surgery. She was prescribed nonsteroidal anti inflammatory drug (NSAID) which reduced the pain intensity. The pain persisted for 4 years. The patient delivered her second child.
In 1990, the patient had a recurrent left ovarian cyst. She underwent a second laparotomy for removal of the cyst. The laparatomy revealed a schwannoma on the left S1 nerve root and a biopsy was taken. Directly after the operation, she had severe pain.
A year later, the patient had surgical excision of the left S1 nerve root at the plexus along with the schwannoma. Following the surgery, she experienced pain upon sitting and touch, and had a limp in her left leg. She was prescribed NSAIDs, antidepressant and pregabalin.
Throughout 1991–2006, despite the pharmacological treatment, the patient had persistent mild pain. In 2006, pain severity increased and was referred to our institution for pain management.
Upon physical examination, the incision from her previous surgery was 4 cm away from the sacral midline and parallel to S1 and S2. The length of the incision was 3 cm. The patient had severe allodynia upon palpation at the area between S1 and L5 and the visual analog scale (VAS) score increased from 3 to 10. She had severe pain at rest and movement. She was not able to sit down properly.
Her neurologic exam revealed a normal mini mental state examination (MMSE), cranial nerves, right side and left upper limb status. The left lower extremity motor power showed mild weakness (4/5 Medical Research Council Scale, MRCS) in the leg abduction (gluteus medius minimus), 4/5 in foot eversion (peroneous longus muscle), 4/5 in the plantar and toes flexion (gastrocnemius/soleus and intrinsic foot muscles) and 3/5 in the hip extension (gluteus maximus muscle). The sensory exam showed severe reduction in pinprick and temperature sensation in the lateral aspect of foot, lower leg and dorsolateral thigh and buttocks. The left ankle jerk was absent.
We decided to perform nerve block. Nerve stimulator guided injection was performed at the pain trigger point being 1 cm above the midline of the incision. Upon nerve stimulation the contraction of the gluteal muscle was observed. Then, 20 mL of the anesthetic mixture were injected. Each 20 mL of the injected mixture contained: 5 mL lidocaine 2%, 5 mL lidocaine 2% with epinephrine 5 μg/mL, 8 mL bupivacaine 0.5%, and 2 mL clonidine 150 μg/mL.
The patient had immediate pain relief after the block (VAS 1/10). She remained pain free for 15 days after which pain reappeared but with less severity (3/10). Repetitive nerve block was performed in a progressive manner. First, she received the nerve block once per month for a year. Then, the pain intensity decreased to 1/10 and thus the frequency of receiving the nerve block was reduced to 1–2 times per year. This frequency is persistent till present time. Currently the patient is not taking any medication.
The most common treatment of schwannoma is by surgical excision . Our case had resection of the schwannoma and excision of the left S1 nerve root causing injury to the corresponding nerve which led to neuropathic pain.
Pharmacological treatment for neuropathic pain usually includes antidepressants, calcium channel α2-δ ligands such as pregabalin, in addition to morphinics . Our patient did not respond to pharmacological treatments except for NSAID drugs which decreased her pain. However, she developed gastric pain and had to stop NSAIDs.
Nevertheless, repetitive nerve block provided effective relief of neuropathic pain. Neuropathic pain occurs when the nervous system is injured and changes in its sensitivity may become persistent. These changes in peripheral signal processing can cause altered central pain processing and central sensitization . Pain can happen spontaneously such that innocuous stimuli lead to pain .
Repeated ilioinguinal block using a catheter technique was shown to be effective in relieving pain caused by inguinal neuralgia . However, the catheter technique was not suitable in this case since it was not possible to place a catheter in the gluteal region. Yet, repeated nerve block might have allowed for prolonged prevention of central and peripheral sensitization. It is possible that this interrupted the neural circuit between nociceptors, central nervous system and motor unit; thus leading to pain alleviation . This could imply that blocking the trigger signal from reaching the central nervous system may narrow the window of pain by reducing the increased sensitivity to painful stimuli and central sensitization in addition to allodynia which accompany tissue injury.
In the present case, the block was not successful three times since the patient felt pain the day after receiving the block; so the block was repeated. The nerve stimulator was used to approximately locate the nerve injury and to inject the anesthetic mixture close to the nerve since we did not have ultrasound at that time. However, a disadvantage of the use of nerve stimulator is that it is not possible to determine the exact location and spread of the injected mixture.
In conclusion, the patient pain intensity decreased and her quality of life improved. Hence, repetitive nerve block could be effective in managing neuropathic pain.
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About the article
Published Online: 2018-02-10
Published in Print: 2018-01-26
Research funding: None declared.
Conflict of interest: None declared.
Informed consent: Published with the written consent of the patient.
Ethical approval: Not applicable.
Citation Information: Scandinavian Journal of Pain, Volume 18, Issue 1, Pages 125–127, ISSN (Online) 1877-8879, ISSN (Print) 1877-8860, DOI: https://doi.org/10.1515/sjpain-2017-0155.