痛覚変調性疼痛の最近の話題

Nociplastic Pain Topics

はじめに

　痛覚変調性疼痛は，侵害受容器の活性化も神経障害もなく，痛覚処理・制御回路の可塑的な変化によって生じる痛みである。だが，このように原因なく生じる痛み体験がある，ということを突き詰めて考えると，痛みとは本当は何なのか，という問題にたどり着かざるをえない。痛覚変調性疼痛の概念は，そんな疑問を突き付けてくる。

　まず，痛覚変調性疼痛という概念がどうして必要とされ，この言葉が生み出されたのか，理解しておく必要がある。まず簡単にその定義と歴史について述べ，そして，“最新の話題” を紹介する。

　The International Association for the Study of Pain（IASP）recognizes three mechanistic categories of pain：nociceptive, neuropathic, and nociplastic pain. These categories describe the underlying mechanisms of pain rather than the pain’s classification or diagnosis. This categorization aims to（ⅰ）clarify the biological processes that generate pain,（ⅱ）facilitate the selection and development of mechanism-based treatments for the pain, and（ⅲ）promote innovation in novel therapeutic strategies for pain. Nociplastic pain, as a term proposed in 2017, is defined as pain arising from altered central nociceptive processing without tissue injury or nerve damage. The concept of nociplastic pain challenges the traditional view that pain necessarily results from peripheral tissue or nerve injury, and in turn, it deepens the inquiry into the essence of pain itself, i.e., how the brain generates the unpleasant sensory-and-emotional experience afforded by pain. The IASP Terminology Task Force is developing a Pain Descriptor Discrimination Tool that clinicians can implement to differentiate among the three mechanistic pain categories with the use of patient self-reports, clinical evaluations, and expert assessments. The mechanistic understanding of nociplastic pain is also being advanced by genomic and transcriptomic research such as genome-wide association studies（GWAS）and transcriptome-wide association studies（TWAS）applied to chronic overlapping pain conditions, together with diverse preclinical models. The concept of nociplastic pain may replace our canonical cause-and-effect understanding of pain with a more brain-centric view, leading to deeper insights into the biological and evolutionary significance of pain.