Proposal to refine the mechanistic classification of chronic pain and corresponding clinical symptomatology

The management and treatment of patients suffering from chronic pain must be based on a precise understanding of the pathophysiological mechanisms underlying the syndrome. However, it cannot be defined solely by the presence or absence of disease or injury affecting either non-neuronal tissues or the neuronal structures of the somatosensory system, as these elements do not always accurately or causally reflect the underlying mechanisms of the pain experienced by patients. The current taxonomy of chronic pain classically includes three main mechanisms: nociceptive, neuropathic, and nociplastic. However, certain ambiguities of this classification need clarification, such as: (1) the importance given to demonstrating a lesion of the somatosensory nervous system for the diagnosis of neuropathic pain; (2) the specificity of sensory descriptors for the diagnosis of neuropathic pain; (3) the imprecision of the concept of "central sensitization". In this article, a new taxonomy is proposed, identifying: (1) differential mechanisms of neuropathic pain related to "large" or "small" nerve fiber systems; (2) "sensory", "cognitive", and "emotional" components of nociplastic pain; (3) "sensory nociplastic pain", which can be distinguished from neuropathic pain by the presence of diffuse, variable, and multiform "neuropathic-like" symptoms; (4) a modulator linked to sensitization related to psychosocial vulnerability and stressors. A comprehensive understanding of the mechanisms of pain relies on a rigorous interpretation of patients' symptoms. It is particularly important to determine whether sensitization mechanisms are present from disease onset, suggesting primary nociplastic pain, or whether they emerge over time, reflecting secondary processes of nociceptive or neuropathic pain syndrome chronification.