Pain has been one of the most intolerable sufferings of human beings. A specific theory by Descartes (1596-1650) had been the basis of pain science until the gate control theory was published in 1965. This new and revolutionary theory has focused on the modulation of sensory input at the spinal cord level, and information has been accumulating since this revolutionary theory. However, a newer theory has yet to be established to solve such clinical phenomena as phantom limb pain, chronic intractable pain, placebo effects, and similar related classifications. Pain clinicians are privileged to get ideas from patients, and the ideas would be beneficial for epoch-making treatments, as well as for developing new concepts or paradigms related to pain.
The basic knowledge of pain mechanisms is summarized here to help pain clinicians diagnose and treat patients from the scientific point of view.

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We compared the utility of predicting the skin-epidural space distance by using various imaging modalities. Subjects comprised patients meeting the indications for lumbar epidural block who had undergone magnetic resonance imaging, radiography and computed tomography for primary disease. Skin-epidural space distances from these modalities were estimated using computed calculating functions of the imaging system. Immediately after the use of ultrasonography to estimate the distance between the skin and dura mater in short-axis and longitudinal views in the lateral position, epidural puncture was performed using a median approach. Puncture distance between the skin and epidural space was recorded. Skin-epidural space distance as estimated by each modality correlated significantly with puncture distance (p<0.001), body weight (p<0.01) and body mass index (p<0.001). In particular, ultrasound imaging showed the highest correlation to puncture distance (r=0.96, p<0.001). In conclusion, ultrasound imaging can predict skin-epidural distance with high correlation to the actual puncture distance, and it could allow adequate and safe epidural block.

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We report a patient who developed involuntary movement of the lower limbs, probably caused by spinal myoclonus, after bolus injection of a local anesthetic into the epidural space. An 86 year-old woman with postherpetic neuralgia received a bolus epidural injection of 1 % mepivacaine 6 ml via an indwelling epidural catheter. Involuntary movement of the right lower limb began 30 min after the injection. The intensity and frequency of this movement increased, and the same abnormal movement of the left lower limb also developed 45 min after the mepivacaine injection. The patient was alert during the episode; however, she could not restrain the abnormal movements, which began to subside in each limb after one hour, gradually resolved, and completely disappeared 3 hr after the injection. She could ambulate after the episode, and MRI of the spinal cord disclosed no abnormalities around the epidural catheter. However, syringomyelia was found in the cervical spinal cord (C4 to C7). We conclude that the cause of the involuntary movement of the lower limbs of this patient was spinal myoclonus, because no mechanical stimulation was caused by the epidural catheter, hematoma, or nerve damage.

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We have reported the effectiveness of intrathecal lidocaine and steroids in the five elderly patients (aged 74 to 83) who had refractory low back and/or lower limb pain originated from multiple operations on their backs. They were treated with epidural block three times and simultaneously daily orally administered for treatment with 150 mg of mexiletine, 15 mg of baclofen (these dosage were divided by 3), and 25 mg of amitriptyline (before sleep). However, neither the low back pain nor the lower limb pain decreased. Intrathecal block by 1 ml of 0.5% lidocaine and 3.3 mg of dexamethasone sodium phosphate was continued 7 times at 2-weeks intervals. The patients were assessed their pain intensity with pain scores used by a visual analogue scale (VAS, mm) 14 weeks later. Pain scores at before treatment were 74 mm in case one; 62 mm in case two; 81 mm in case three; 78 mm in case four; and 100 mm in case five. Pain scores after treatment were 33 mm, 60 mm, 5 mm, 29 mm and 25 mm, respectively. Although the pain score decreased in 4 cases, it did not decrease in case 2 because this patient complained of widespread low back and lower limb pain. An intrathecal block with local anesthetics containing glucocorticoid might be useful for the pain management in backs that have undergone multiply operations.

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This case report reveals that the crowned dens syndrome (CDS) that developed after clinical trial drug administration for postherpetic neuralgia (PHN) was difficult to diagnose. The patient, a 78-year-old woman, decided to participate in Phase III trials of buprenorphine tablets as treatment for left chest pain that developed shingles. After the trial started, the PHN pain was reduced, but she suffered intense neck pain, warmth, and limited neck retro flexion. A spinal CT scan revealed faint calcified deposits on the transverse ligament of the atlas, and CDS was diagnosed. One week after administration of the nonsteroidal anti-inflammatory drugs, the neck pain had disappeared.
The CDS, its rapid onset, presents the intense neck pain and a limited range of motion. The diagnostic evidence is calcification around the transverse ligament of the atlas and dens and the intense inflammatory response. We must seriously suspect CDS in a patient afflicted with a rapid onset of neck pain and a limited range of motion.

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A 52-year-old woman suffered from severe lumbago and left sciatica. A lumbar MRI revealed a cystic lesion in the lumbar spinal canal. Based on these findings, a synovial cyst of a lumbar facet joint was presumed. A variety of medications and epidural blockades did not improve her pain.
After that, we performed an epiduroscopy (EDS) procedure to puncture the cyst. By introducing a contrast medium into the lumbar epidural space through the EDS, we identified a circular non-staining region and diagnosed it as the cyst. The cystic wall was so firm that we did not insert the EDS, but we could insert a needle into the circular region through the interlaminar space between the 4th and 5th lumbar vertebrae and thus decompress the cyst. Immediately after this, her pain improved.
At the present time, she is drug-free with little pain. This case favorably suggests minimum invasive intra-spinal canal surgery for decompression of the radicular nerve in the future, using the EDS as a support to identify the lesion.

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We report a successful case of intercostal block in a 51-year-old female patient who could not take oral medication. She underwent resection of oro- and hypopharynx cancer and reconstruction with jejunum. Her cancer was unresponsive to chemotherapy, radiation, and palliative care with a fentanyl patch, oral opioid medication, and pregabalin. Metastasis developed in the right thorax, and pain and nausea prevented her from taking oral medicine. CT revealed an invasion of cancer to costal bones; neuropathic pain was suspected. Intravenous morphine and ketamine were ineffective. Intercostal nerve block was effective for pain relief of the right chest. After gastric fistula surgery for a definite drug administration route, she was discharged uneventfully for home care.

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We report a home-care patient who received multiple radiofrequency thermocoagulation(RFT) to relieve cancer pain without increasing opioid dosage. A 46-year-old man had an uncontrollable lumbar backache and a lower-extremity weakness caused by bone metastases from pancreatic cancer. We provided epidural and intercostal nerve blocks and increased opioid dosage. As the cancer became advanced with accompanying spinal cord damage and respiratory failure he needed hospitalization. But he was discharged with domiciliary oxygen therapy because he desired to die at home. Rest pain was well controlled by opioid patch, but movement-exacerbated pain was not. Increasing the dosage was limited by a side-effect of somnolence. After RFT was applied at home to the Th6 and Th7 intercostal nerves and to the Th7 nerve roots at the hospital, opioid dosage decreased by half and somnolence disappeared. He received treatment with RFT on the Th3 and Th4 intracostal nerves, and he could work at home until just before death, as he had wished. The nerve blocks are useful even during home visit treatment.

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We report 3 patients with phantom limb pain and phantom limb sensation after an operation for forequarter amputation whose pain was relieved by oral gabapentin. Case 1 had phantom pain 14 days after amputation. The pain was relieved with a dose of 300 mg/day of oral gabapentin, and the numerical rating scale (NRS) was improved from 8/10 to 0~1/10. Case 2 had a neuropathic pain caused by a tumor of humerus before amputation, and oral gabapentin was administered at a dose of 300 mg/day. Pain was relieved and NRS was improved from 5/10 to 3/10. Oral gabapentin at the same dose was also effective for relieving a phantom sensation that occurred 9 days after the operation. Case 3 had phantom pain 2 days after amputation. Pain was relieved with a dose of oral gabapentin, 600 mg/day, and NRS was improved from 6/10 to 2/10.
The results in these cases suggest that oral gabapentin is effective for the relief of phantom pain and phantom sensation after amputation.

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[in Japanese]

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