Physiology and pathophysiology of chronic pain (Part II): how does pain become chronic?

Abstract

Chronic pain occurs when pain transitions from an acute to a chronic state, especially when acute pain is not effectively managed. In the presence of continuous acute pain, pain processing and pathways gradually undergo several structural and functional modifications in a process known as sensitisation. These modifications may occur in the peripheral or central nervous system. The consequences of these modifications include decreased pain threshold, increased excitability and increased responsiveness to pain. A combination of all of these changes result in the conversion of acute to chronic pain. This review summarises the pathophysiological alterations that are involved in pain chronification. However, these changes and mechanisms are not as simplistic as presented here, as the mechanisms involved are far more complex. The presentation adopted is for the benefit of a basic understanding and not a comprehensive treatise on chronic pain mechanisms.