We reviewed the recent progress in the ability of electroencephalography (EEG) and magnetoencephalography (MEG) to detect pain perception in humans. Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), which reflect metabolic or blood flow changes by painful stimulation, have excellent spatial resolution in the order of mm, but their temporal resolution is not very high. In contrast, EEG and MEG, which reflect physiological changes, have an excellent temporal resolution in the order of msec, however, it is difficult for EEG and MEG to detect activities in deep areas such as the thalamus. Since the spatial resolution of EEG is not very high in the order of cm, MEG is useful for detecting activated areas following painful stimulation.
For recording activities following Aδ fiber stimulation relating to the first pain, MEG were usually recorded following painful CO₂ laser stimulation, but our new method, epidermal stimulation (ES), is also very useful. The primary small activity was recorded from the primary somatosensory cortex (SI), probably in area 1, in the hemisphere contralateral to the stimulation. Then, the secondary somatosensory cortex (SII) and insula were activated with the second activity in SI. These three regions were activated in parallel with almost the same time period. This is a very characteristic finding in pain perception. Then, the cingulate cortex and medial temporal area (MT) around the amygdala and hippocampus were activated. In the hemisphere ipsilateral to the stimulation as well, the above regions were activated, except for SI. Therefore, SI is considered to play a main role in localization of the stimulus point, the SII and insula are important sites for pain perception, and the cingulate and MT are mainly responsible for cognitive or emotional aspects of pain perception.
For recording EEG and MEG activities following C fiber stimulation relating to the second pain, we recently developed a new method of applying weaker CO₂ laser stimuli to tiny areas of the skin. MEG findings following C fiber stimulation were also similar to those following Aδ fiber stimulation. However, the effect of sleep and attention on MEG following C fiber stimulation was much larger than that following Aδ fiber stimulation. This findings may suggest the greater effects of cognitive or emotional functions on the second pain than on the first pain.

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Epidural abscess has been rarely reported as a complication of stellate ganglion block (SGB). We treated a case of epidural abscess, brain abscess and meningitis probably caused by SGB. A 63-year-old male who had an accidental finger injury suffered from CRPS type II. He visited this city hospital and received treatment for SGB several times a week. After treatment for six years, he complained of cervical back pain and progressive stump pain, and developed fever. He then visited our pain clinic and received MRI examination. It showed cervical and lumbar epidural masses and cerebrospinal fluid was xanthochromic. He was diagnosed as having epidural abscess and meningitis. Antibiotic therapy was initiated immediately and he was followed with MRI examination during this treatment. Finally, antibiotic therapy successfully reduced his abscess and surgical decompression was not required. He recovered without significant neurological deficitis. We should be aware of relatively rare complications of epidural abscess and meningitis associated with SGB even if a patient does not have a risk factor of infection.

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We report six patients with cervicogenic orofacial pain. No craniofacial lesions were found in the patients; however, palpation of the neck disclosed trigger points in the cervical muscles and tender points at the transverse processes of the affected side in all patients. Each patient received local anesthetic injection into the painful areas, painful muscles, and deep cervical plexuses. Local anesthetic injection into the painful areas did not relieve the pain. Local anesthetic injection into the trigger points relieved the pain; however, the pain relief was not complete. Deep cervical plexus block with a local anesthetic relieved the pain, but injection of normal saline was not effective. Clinicians should be aware of cervicogenic orofacial pain.

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We report a case of varicella-zoster virus myelitis. A 85-year-old female complained of spastic pain in her right anterior thigh on the 13th day after the onset of herpes zoster on the right L1 dermatome. Continuous epidural block was performed to relieve the pain. On the 18th day she noticed muscular weakness of the right lower limb. Neurologic examination showed disturbance of noxious and temperature sensations lower than left T11 and bilateral hyperreflexia of the patellar tendons on the 21st day. High signal intensity area in the center of the spinal cord between T9 and T10 was demonstrated by T2-weighted magnetic resonance imaging (MRI). High level varicella-zoster virus antibody was found in the cerebrospinal fluid. The possibility of myelitis should be considered when a patient with herpes zoster complains of motor paresis.

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