Chronic pain is a major health problem, affecting 10–30% of the population in developed countries. While chronic pain is defined as “a persistent complaint of pain lasting for more than the usual period for recovery,” recently accumulated lines of evidence based on human brain imaging have revealed that chronic pain is not simply a sustained state of nociception, but rather an allostatic state established through gradually progressing plastic changes in the central nervous system. To visualize the brain activity associated with spontaneously occurring pain during the shift from acute to chronic pain under anesthetic-free conditions, we used manganese-enhanced magnetic resonance imaging (MEMRI) with a 9.4-T scanner to visualize neural activity-dependent accumulation of manganese in the brains of mice with hind paw inflammation. Time-differential analysis between 2- and 6-h after formalin injection to the left hind paw revealed a significantly increased MEMRI signal in various brain areas, including the right insular cortex, right nucleus accumbens, right globus pallidus, bilateral caudate putamen, right primary/secondary somatosensory cortex, bilateral thalamus, right amygdala, bilateral substantial nigra, and left ventral tegmental area. To analyze the role of the right amygdala in these post-formalin MEMRI signals, we repeatedly inhibited right amygdala neurons during this 2–6-h period using the “designer receptors exclusively activated by designer drugs” (DREADD) technique. Pharmacological activation of inhibitory DREADDs expressed in the right amygdala significantly attenuated MEMRI signals in the bilateral infralimbic cortex, bilateral nucleus accumbens, bilateral caudate putamen, right globus pallidus, bilateral ventral tegmental area, and bilateral substantia nigra, suggesting that the inflammatory pain-associated activation of these structures depends on the activity of the right amygdala and DREADD-expressing adjacent structures. In summary, the combined use of DREADD and MEMRI is a promising approach for revealing regions associated with spontaneous pain-associated brain activities and their causal relationships.

Osteoarthritis of the knee impairs activities of daily living of those affected. Its irreversible degenerative changes to the knee joint induce functional disturbance and unpleasant arthralgia. The pain has inflammatory components and often is manifested with mechanical allodynia and hyperalgesia. Sustained weight bearing and joint movements increase pain sensitivity in knee osteoarthritis. Understanding the mechanisms underlying the mechanical allodynia and hyperalgesia might provide a therapeutical target for pain relief in patients with such symptoms. Piezo channel is a mechanically activated ion channel that may be involved in mechanical transduction in the articular cartilage. Although it has been shown that inflammation potentiates Piezo channel current induced by mechanical stimulation, whether Piezo expression levels are influenced by knee osteoarthritis has remained unknown. We measured Piezo mRNA in knee joints and dorsal root ganglia after establishing a model of knee osteoarthritis in rats using monosodium iodoacetate and found Piezo mRNA level is not upregulated. This finding raises a question as whether and how Piezo channels may be involved in mechanically induced pain in osteoarthritis.

Case: A 58-year-old man presented with lumbar spinal stenosis due to epidural lipomatosis. He underwent transsacral canal plasty (TSCP), in a manner similar to epidural adhesiolysis, which can be performed under local anesthesia. His leg pain improved dramatically in the year after surgery. Furthermore, magnetic resonance images during this time show neural decompression by reduction of the amount of epidural fat.Conclusion: TSCP was found not only to relieve pain but also to achieve neural decompression in this patient with spinal canal stenosis caused by lumbar epidural lipomatosis. This is the first report to demonstrate the usefulness of TSCP for spinal epidural lipomatosis.Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSCC/ B975).

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Background: Skeletal-related events due to spinal metastasis in cancer significantly impair patients’ activities of daily living and quality of life. Most of these events occur suddenly. To reduce their impairment occurred suddenly, and to allow them to return to their normal life immediately, many patients undergo palliative surgery; however, some patients do not improve their performance status (PS) as expected. There is little evidence regarding the factors influencing a patient’s PS after palliative surgery. We aimed to investigate the pre-operative predictors of poor PS 1 month after surgery.Methods: The study included a consecutive series of 71 patients with pathological spinal fracture who underwent palliative surgery. Pre-operative predictors of poor post-operative PS were investigated. The participants were categorized into two groups according to PS; the Good group (PS 0, 1, or 2) and the Poor group (PS 3 or 4). We performed univariate and multivariable logistic regression analyses on demographic information, unidentified primary site, AIS grade, poor PS, spinal instability neoplastic score, revised Tokuhashi score, New Katagiri score, modified Glasgow Prognostic Score (mGPS), neutrophil-lymphocyte ratio(NLR), and prognostic nutrition index (PNI). Results: Post-operatively, the Poor group included 38.0% of the patients. Univariate analysis revealed that the following pre-operative factors were related to poor outcomes (p<0.05): BMI<18.5; AIS grade C; poor PS; revised Tokuhashi score 0−8; New Katagiri score 7−10; mGPS 2; and PNI. In the multivariate analysis, mGPS 2 (OR = 22.8, 95% CI = 2.59−202.00, p<0.01) was a significant pre-operative predictor of poor post-operative PS. Conclusion: mGPS 2 was a predictive clinical factor that influenced PS 1 month after surgery. Patients with mGPS 2 should be carefully evaluated to determine their treatment, especially whether they should undergo palliative surgery.