Although chronic pain due to diabetic neuropathy, defined as painful diabetic neuropathy (PDN), is a debilitating and distressing complication of diabetes, epidemiological data on PDN has been scarce, especially in Asia. We evaluated the prevalence of Japanese PDN and its impact on their quality of life (QOL) and metnal state. In addition, we examined to which extent physicians are aware of patients' PDN. A total of 298 patients with diabetes were found to be eligible for the study. We revealed that substantial percentage (22.1%) of Japanese diabetic patients had PDN and that PDN had negative effect on patients' QOL and mental state. However, physicians were aware of PDN in only 36.4% of patients with the condition. To the best of our knowledge, this is the first report showing the extent of physicians' awareness of patients' PDN. In conclusion, physicians treating diabetes need to be more aware of patients' PDN in everyday clinical practice to prevent the progression of PDN and improve the patients' QOL and mental state.

Purpose This study aimed to investigate whether changes in psychosocial factors and pain severity were associated with reduction in disability due to pain among patients with chronic pain. We hypothesized that increased self-efficacy would reduce disability. Patients and methods This longitudinal observational study included 72 patients. Patients’ psychological and physical variables were assessed before and after 3 months of treatment. Demographic and clinical information were collected, including the Pain Disability Assessment Scale (PDAS), the Pain Self-Efficacy Questionnaire (PSEQ), the Hospital Depression and Anxiety Scale, and the Numeric Rating Scale (NRS) to assess pain intensity. First, univariate regression analyses were conducted to clarify associations between change in PDAS and sex, age, pain duration, changes in psychosocial factors (self-efficacy, anxiety, and depression) and change in pain intensity. Second, multivariate regression was conducted using the variables identified in the univariate analyses (PSEQ and NRS) to detect the most relevant factor for reducing disability. Results Univariate regression analyses clarified that changes in PSEQ (β = −0.31; 95% CI: −0.54–−0.08, p = 0.008) and NRS (β = 0.24; 95% confidence interval [CI]: 0.01–0.47, p = 0.04) were associated with reduction in PDAS. Multivariate regression analysis demonstrated that change in PSEQ (β = 0.26; 95% CI: −0.50–−0.02; p = 0.01) was associated with a reduction in disability, independent of change in NRS. Conclusion These findings suggest improved self-efficacy is associated with reduced disability in patients with chronic pain, independent of reduction in pain intensity. Focusing on improvement in self-efficacy may be an effective strategy in chronic pain treatment in addition to pain relief.

Variation in the production of opioid receptors over a 24-h period is considered to contribute to circadian alterations in neuropathic pain. In this study, we investigated the possible changes in the circadian rhythm of mRNA expression for µ-opioid receptor (MOR), κ-opioid receptor (KOR), and adrenaline α2a receptor (α2a) in the periaqueductal gray, frontal cortex, thalamus, and spinal cord following sciatic nerve ligation in mice. In sham-operated mice, the latencies of hind paw-withdrawal in response to thermal stimuli at 14:00 and 20:00 were significantly greater than that at 8:00 and the latency at 2:00 was significantly less than those at 14:00 and 20:00, indicating a "rest" period-dominant circadian rhythm for thermal pain-thresholds. In sciatic nerve-ligated mice, the latencies of hind paw-withdrawal in response to thermal stimuli at 14:00 and 20:00 were significantly less than that at 8:00, and the latency at 2:00 was significantly greater than those at 14:00 and 20:00. A correlative tendency between the time-variation of pain latency and the time-variation of MOR mRNA expression was observed in the periaqueductal gray of sham-operated and sciatic nerve-ligated mice. In contrast, neither mouse showed a strong circadian rhythm for the expressions of KOR and α2a mRNAs in any region. The present data suggest that changes in MOR mRNA expression in the periaqueductal gray may be synchronized with the circadian rhythm for the pain threshold for noxious thermal stimuli. In contrast, neuropathic pain in mice exhibited a negative circadian pattern for the expression of MOR, KOR, and α2a receptors in the frontal cortex, thalamus, and spinal cord.

BackgroundOxycodone is one of the options for the management of CLBP in patients with an inadequate response to other analgesics. However, oxycodone is not yet approved for noncancer pain in Japan. Here, we assessed the efficacy and long-term safety of S-8117, a controlled-release oxycodone formulation, for the management of Japanese CLBP patients.Patients and methodsAn initial enriched enrollment randomized withdrawal, double-blind, placebo-controlled, 5-week phase III trial was conducted across 54 centers in Japan to assess the efficacy of S-8117 vs placebo in moderate-to-severe CLBP patients. Subsequently, a 52-week, open-label, single-arm study was conducted across 53 centers in Japan to evaluate the long-term safety of S-8117. The primary endpoint was the time to inadequate analgesic response during 35 days of the double-blind period. Secondary endpoints were the percentages of patients with inadequate analgesic response, discontinuation rate due to inadequate analgesic effects or AEs, and changes in scores of BPI severity, BPI pain interference, SF-36, and Roland-Morris Disability Questionnaire. Safety was assessed as the incidence of AEs and ADRs.ResultsOf the 189 patients enrolled in the double-blind study, 130 patients who completed the initial titration period were randomized 1:1 to receive either S-8117 (n=62) or placebo (n=68). Baseline characteristics were comparable across the study groups. The time to inadequate analgesic response was significantly longer in patients treated with S-8117 than placebo (P=0.0095). Secondary endpoints corroborated the efficacy of S-8117 vs placebo. Overall, 478 AEs were reported in 73/75 patients in the long-term study. The most frequent ADRs were somnolence, constipation, and nausea. No case of drug dependence was reported in the long-term study.ConclusionShort-term efficacy vs placebo and long-term safety of S-8117 were demonstrated for the management of Japanese patients with moderate-to-severe CLBP.

Several clinical reports on neuropathic pain of various etiologies have shown that it significantly interferes with sleep. Inadequate sleep due to neuropathic pain may contribute to the stressful negative consequences of living with pain. It is generally recognized that melatonin (MT) system in the hypothalmus is crusial for circadian rhythm and sleep-wake transition. However, little, if any, is known about whether neuropathic pain could affect the MT system associated with sleep disturbance. In this study, we investigated the possible changes in circadian rhythm for the expression of MT receptors, especially MT1A and MT1B receptors, in the hypothalamus of mice with sciatic nerve ligation. The samples for real-time RT-PCR assay were prepared at 8:00, 14:00, 20:00, and 2:00 on day 7 after sciatic nerve ligation or sham operation. The mRNA expression of MT1A and MT1B receptors at 2:00 in sciatic nerve-ligated mice, which exhibited thermal hyperalgesia along with an increase in wakefulness and a decrease in nonrapid eye movement sleep, was significantly greater than those in sham-operated mice, whereas the levels of both MT1A and MT1B receptors at 8:00 in sciatic nerve-ligated mice were significantly lower than those in sham-operated mice. These findings suggest that neuropathic pain-like stimuli lead to sleep disturbance in parallel with changes in circadian rhythm for mRNA expression of MT 1A and 1B receptors in the hypothalamus of mice.