In any observational study where an exposure of interest, such as pharmaceutical treatment, is not randomly assigned to subjects, a bias is often introduced in estimating the true effect of treatment. This is because patients who receive treatment usually have more severe medical conditions than those without treatment. Failure to control such inherent bias in patient characteristics when assessing for the true effect of treatment across comparison groups, may lead to confounding. The presence of confounding makes it difficult to evaluate the true treatment effect. In this paper, we will introduce statistical strategies which aim to remove the effects of confounding in observational studies.

Smoking is associated with the occurrence of various cancers. However, some patients continue to smoke despite being diagnosed with cancer. Smoking has a negative impact on pain. Among cancer patients, pain affects quality of life (QOL) most significantly. Smokers have been reported to have a greater frequency and severity of cancer-related pain than non-smokers. Although experimental studies have shown that acute exposure to nicotine has an analgesic effect, chronic exposure to nicotine alters pain processing in smokers. In addition, nicotine withdrawal may induce hyperalgesia. Smoking can also interfere with wound healing, and interact with various drugs such as analgesics, which may exacerbate the pain condition. Moreover, pain increases the desire for smoking. Typically, the patient falls into a vicious cycle of pain and smoking. Therefore, in order to maintain the QOL of cancer patients, it is important to support smoking cessation in parallel with pain management, from the time of diagnosis.

One of the major complications affecting the activity of daily living (ADL) in the patients with Buerger's disease is the amputation of the extremities due to serious ischemia and resultant necrosis. There are many patients with Buerger's disease who are resistant to such treatments as pharmacological interventions, lumbar sympathetic ganglion block, and surgical revascularization. We have introduced spinal cord stimulation (SCS) treatment in a patient with Buerger's disease, resistant to those treatments. The effect of SCS was evaluated using the skin perfusion pressure (SPP). SPP was less than 30 mmHg prior to SCS, and defined as critical limb ischemia (CLI), but increased to greater than 40 mmHg 3 months after SCS with better ADL. For the patients with CLI, it is possible that SCS might improve peripheral perfusion, thus improve CLI, which can be monitored by SPP.

We report the case of a 56-year-old female suffering from right lower limb pain. She was diagnosed with idiopathic multiple mononeuropathy by the Department of Neurology and referred to us for pain control. The patient showed claudication in her gait due to pain. Her pain measured 29 mm on the visual analogue scale (VAS). Lumbar epidural blocks (three times/month) were ineffective. However, ultrasound-guided popliteal sciatic nerve blocks (four times/month) contributed to improvement. Multiple mononeuropathy is a disease in which inflammation occurs in peripheral nerves due to conditions such as metabolic diseases, drugs, and collagen diseases. The epidural block was ineffective, but the sciatic nerve block was effective in this case. The direct penetration of local anesthesia at the region of neuritis shows an anti-inflammatory effect, and improved the symptoms. This suggests that a peripheral nerve block may improve symptoms relating to diseases in which a nerve block near the central axis has not been effective.

This retrospective study aimed to test the hypothesis that pulsed radiofrequency (PRF) may enhance analgesic effect and provide symptomatic improvements for patients with herpes zoster-related pain. Seven patients with herpes zoster-related pain who underwent PRF in 2016 were enrolled. The sample included four males and three females. The mean age was 71.2±12.3 years old. Of the seven patients, PRF was administered once in five patients, twice in one patient, and three times in one patient. The interval from the onset of herpes zoster to the first administration of PRF ranged from 42 days to 5.3 years. After PRF, the visual analogue scale (VAS) for pain scores improved and clinical symptoms including allodynia were ameliorated, in six patients, regardless of their disease durations. There were no reported complications. Further larger scale prospective trials are needed to evaluate the efficacy of PRF including its duration of effectiveness at each clinical stage.

Complex regional pain syndrome (CRPS) accompanies allodynia. Allodynia impairs the quality of life in chronic pain patients and is often difficult to treat. It has been suggested that yokukansan has an anti-allodynic effect. In this case report, shichimotsukokato was administered to a patient with CRPS who could not continue to take yokukansan. Shichimotsukokato provided the same anti-allodynic effect as yokukansan. Shichimotsukokato contains chotoko, which is the active constituent leading to anti-allodynia action in yokukansan. This case suggests that shichimotsukokato may offer similar anti-allodynia effect as yokukansan.

Background: Cerebellopontine angle epidermoid is a rare congenital tumor. This is a slow growing benign tumor with late presentation in adulthood. There is a possibility of missed diagnosis. Case Presentation: A 56 year-old woman had intermittent left cheek pain for 10 years. The patient was diagnosed with typical trigeminal neuralgia (TGN) at a general hospital. She was treated with a satellite ganglion block and oral medication. As a typical trigeminal neuralgia, the nature of pain was atypical. During the first examination, sensory disturbances in the second branch of the trigeminal nerve in the left side and delayed light reflexes of the left pupil were detected. Cranial magnetic resonance imaging (MRI) was performed. The result of the MRI showed a cerebellopontine angle epidermoid tumor. TGN resolved completely after near complete tumor resection. Upon removal of the tumor, the patient required no analgesics. Conclusion: We reported a case of TGN due to epidermoid. The diagnosis was made after a thorough neurological examination. Regular MRI is also necessary. This is because symptoms are exhibited even if the tumor is small. To ensure correct diagnosis and treatment, careful case management in the pain clinic is necessary.

A 34 year-old woman, diagnosed with herpes zoster along the mandibular division of the trigeminal nerve, showed severe zoster associated pain (ZAP) of left lower jaw, auricle and tragus. Stellate ganglion block alleviated the pain of lower jaw but strong allodynia of the auricle and tragus was remained. The ultrasound-guided auriculotemporal block was improved the allodynia significantly and the allodynia disappeared after the third block administration. For managing ZAP, when attempting to provide sensory nerve blockage in the auriculotemporal region, we recommend choosing the auriculotemporal block for the periphery and the shallow layer first, followed by the mandibular block or auriculotemporal block at the deep layer. The ultrasound-guided auriculotemporal block may reduce the amount of local anesthetic required and provide the desired effect safely and securely.

A 42-year-old woman with type 1 diabetes, initially admitted to the hospital for the management of ischemic gangrene, received almost daily injections of buprenorphine for associated right foot pain. Subsequently, she underwent off-pump coronary artery bypass graft (CABG) surgery and received pentazocine for post-thoracotomy pain. After several months she was referred to our pain clinic, as she not only had severe pain but also firm expectations for the continued administration of buprenorphine and pentazocine injections. She was therefore diagnosed with opioid dependence. We recommended a transition to oral tramadol and pregabalin. When a fentanyl patch was introduced for the withdrawal symptoms, they disappeared the following day. Following this, we adjusted the prescribed medications for about six weeks, after which she was discharged home. In this case, we strongly suspect an opioid pseudoaddiction through the treatment progress. Furthermore, we propose that fentanyl, which is a pure μ receptor agonist and offers a more stable blood level as a patch, is an effective and safe therapeutic agent for opioid-dependent patients in Japan with limited therapeutic options.

Trigeminal neuralgia results in severe pain from performance of daily living activities, such as eating and face-washing. Moreover, though carbamazepine, which is the initial drug of choice for the treatment of trigeminal neuralgia, has a high efficacy rate, its side effects, including dizziness and drowsiness, reduce mobility. Seven patients with trigeminal neuralgia were treated with scalp acupuncture alone or in conjunction with drug therapy, and their symptoms decreased significantly. The method of scalp acupuncture involves the application of needles to the subcutaneous tissues of the scalp, prior to hitting the periosteum, in the projection of the somatosensory area of Penfield's homunculus. The electroacupuncture are electrically stimulated for 20 min at a frequency of 150 Hz. We have previously reported the efficacy of scalp acupuncture in the treatment of chemotherapy-induced peripheral neuropathy. The possible mechanism of pain relief by scalp acupuncture is that the treatment affects brain neuronal plasticity.

We report a patient with cervicogenic headache who was treated with radiofrequency thermocoagulation of the C2 root. A 29 year-old woman presented in X−8 year with a headache in the left occipital area following a fall from the bed. The headache resolved with medical therapy. In X−4 year, the headache recurred. A stenosis of the intervertebral foramen at C1/2 by a bone splinter was thought to be the cause of the headache from a computed tomography finding. Foraminotomy was performed and the headache disappeared. However, a bone splinter recurred again in X year. Oral medication and physical therapy were not effective; she had difficulty sleeping and working because of the headache. Local anesthetic injection paravertebral to C2 was effective in the short term. She was treated with radiofrequency ablation of the C2 root and the headache was well controlled. This case demonstrated the effectiveness of radiofrequency ablation in treating cervicogenic headache originating from the C2 root.

A 77-year-old man with a history of diabetes was diagnosed with herpes zoster (HZ) involving the mandibular nerve. He was hospitalized in the dermatology department and acyclovir (ACV) administration was initiated. Abnormal behavior observed on the following day raised suspicion of ACV encephalopathy, and the ACV was discontinued. As pain control was insufficient, the patient was referred to the pain clinic. Treatment relieved the pain, and the patient was discharged. On day 51 after onset, he complained of lower-left tooth loss and was referred to our oral surgery department. With the diagnosis of lower-left jaw osteonecrosis, sequestrectomy was performed under general anesthesia. Cases of HZ occurring in a trigeminal nerve branch II and III distribution, with successive loss of teeth and jaw osteonecrosis, have been reported. Physicians should be aware that HZ can be associated with this complication. In the present case, insufficient administration of antiviral drugs for HZ may have been a factor.