The Pain Disability Index (PDI) is a self–reported outcome measure initially developed in English to assess disability caused by pain in seven dimensions of daily life activity, including family ⁄ home responsibilities, recreation, social activity, occupation, sexual behavior, self–care, and life–support activity. This study aimed to develop a linguistical­ly valid Japanese version of the PDI (PDI–J) according to the guidelines for the translation and cultural adaptation of patient–reported outcome measures establish­ed by the task force of the International Society for Pharmacoeconomics and Outcomes Research. A draft of the PDI–J was developed through a forward translation of the original PDI from English to Japanese, reconciliation of the translation, back–translation from Japanese to English, and harmonization. We subsequently conducted a cognitive debriefing in five patients using the PDI–J draft and reviewed it before finaliz­ing a linguistically valid PDI–J. We also considered a five–item version of the PDI (PDI–5–J), which excluded two items (sexual behavior and life–support activity) from the original version. This consideration was made for brevity and because sexual behavior is a considerably personal parameter that some patients may be reluctant to answer and life–support activity because it was considered ambiguous in Japanese. Therefore, we were able to develop a linguistically valid PDI–J and PDI–5–J through this process. Further study is warranted to confirm the psychometric validity and reliabili­ty of the two indices (PDI–J and PDI–5–J).

Objective: Pain severity is associated with structural joint pathology and pain sensitiza­tion in knee osteoarthritis (OA); however, the applicability of these findings to Japanese patients remains unknown. Hence, we investigated the association between either radiologic severity or central sensitization and chronic joint pain in knee OA.

Methods: We divided 43 patients with knee OA into two groups based on the severity of knee joint pain: strong ⁄ severe pain (Group A, n=17) and mild ⁄ moderate pain (Group B, n=26). Radiographic evidence of structural joint pathology was graded according to the Kellgren–Lawrence (K–L) scale. The degree of central sensitization was indexed using quantitative sensory testing (QST), including pressure pain threshold (PPT) and temporal summation of pain (TSP). In order to determine the factors that influence joint pain severity, we compared data from the radiographic assess­ment and QST between the two groups and examined the correlation between pain severity and either radiographic assessment or QST.

Results: There were no significant differences in the K–L scale between patients with either strong ⁄ severe or mild ⁄ moderate joint pain. Those with strong ⁄ severe pain had a lower PPT and higher TSP than did the patients with mild ⁄ moderate pain. In addition, QST was found to be significantly correlated with joint pain.

Conclusion: When measured using QST, we found a significant difference in central sensitization between Groups A and B, whereas radiologic severity did not differ signifi­cantly.

For the perioperative management, acute and chronic postsurgical pain (CPSP) are the urgent medical matters to be considered. The International Association for the Study of Pain (IASP) has named 2017 as the Global Year Against Pain After Surgery where they focused on the pain after surgery. As one of various aspects of postsurgical pain, they had published fact sheet named “Chronic Postsurgical Pain (CPSP): Definition, Impact, and Prevention”. In the fact sheet, they had concluded that “prediction of CPSP might in theory allow preemptive targeting of individual patients at risk”. Pain catastrophizing scale (PCS) could be one of predictive factors for CPSP. As other predictive factors, endo­genous pain modulation, such as conditioned pain modulation (CPM) and temporal summation of pain (TSP) has been reported. In addition, offset analgesia (OA) has been considered to represent the endogenous pain modulation recently. However, it remains unclear whether these preoperative evaluations could lead to the prediction of acute and chronic postsurgical pain. We have developed the portable measurement device for the evaluation of endogenous pain modulation such as CPM, TSP and OA. With the developed device, CPM, TSP and OA were tested in healthy volun­teers and patients scheduled for orthognathic surgery. In addition, PCS scores were recorded preoperatively. The data showed that the preoperative evaluation of CPM, PCS and OA would lead to the prediction of patients at risk for postsurgical pain.

Phantom limb pain is an intractable pain for which no effective treatment has been establish­ed. The pain has been attributed to abnormal plastic changes in the sensory motor cortex corresponding to the deafferented body part. Some feedback therapy such as mirror therapy have been applied to modify the abnormal cortical changes, although it is not been unveiled how to change the corresponding sensory motor cortex to reduce pain.

We have applied neural decoding to magnetoencephalography (MEG) to extract motor information of the upper limb, and realized a Brain–Computer Interface (BCI) that allows patients to operate a prosthetic hand as if they were moving a phantom limb. In addition, we have demonstrated that neurofeedback (NF) training to control the BCI induced plastic changes in the patient’s sensorimotor cortex and changes in the pain. Actually, the training to attenuate the motor representation of the phantom limb reduced the pain.

In addition, we evaluated the efficacy of the NF training by a blinded crossover trial of training with three consecutive days. Twelve patients were trained to control the phantom limb images, that were controlled through BCI. After three days NF trainings, the pain assessed with the Visual Analogue Scale (VAS) was significantly reduced for five days. Furthermore, the pain reduction was associated with the attenuation of the motor representation of phantom limb. These results suggest that the residual motor representations of phantom limb cause the phantom limb pain.

We have demonstrated that the NF training elucidates the pathogenesis of chronic pain and develops a new treatment.

Relationship between chronic pain and cortical activity was shortly reviewed. Change in cortical neural activity in patients with chronic pain has been reported in many previous papers. Those previous reports showed characteristics finding of basic rhythm, such as increment of theta activity, depending on the degree of pain and the pathological condition in patients with peripheral and central chronic pain syndrome. Recent studies, including our studies, suggested quantitative analysis of cortical neural activity, such as current density, frequency distribution, and connectivity between pain–related cortical areas, could evaluate subjective chronic pain. Connectivity analysis also suggested chronic pain might induce modulation of large scale network including default mode network, which resulted in modification of sensory and motor cognition and psychological responses in daily life of patients.