A systematic review of the pain-related emotional and cognitive impairments in chronic inflammatory pain induced by CFA injection and its mechanism.

Researchers reviewed 66 studies to understand how chronic pain affects emotions and thinking. They used a common laboratory model where inflammation is created by injecting a substance called CFA (complete Freund's adjuvant) to trigger pain. The review found that chronic inflammatory pain doesn't just hurt physically—it can also cause anxiety, depression, and problems with memory and thinking. These emotional and mental problems appeared at different times after pain started. Anxiety developed either very quickly (within 1-3 days) or later (2-4 weeks after pain began). Depression typically showed up within four weeks, while thinking and memory problems appeared between 2-4 weeks. The researchers identified specific brain regions and pathways involved in these connections, particularly areas called the anterior cingulate cortex and amygdala, which became overactive and inflamed. They also found that inflammation, stress on cells, changes in gut bacteria, and communication problems between the gut and brain all contributed to these emotional and cognitive issues alongside pain. This research helps explain why people with chronic inflammatory conditions often experience anxiety, depression, and mental fog along with their physical pain. Understanding these connections is important because it suggests that effective treatment should address not just the pain itself, but also the emotional and cognitive symptoms that come with it. Acupuncture may help by reducing inflammation and modulating brain activity in these key areas. If you're experiencing chronic pain with emotional or cognitive symptoms, consult a qualified, licensed acupuncturist experienced in pain management.

This systematic review analyzed 66 experimental studies examining pain-related emotional and cognitive comorbidities in CFA-induced chronic inflammatory pain models. Temporal patterns showed anxiety-like behaviors emerging at 1-3 days or 2-4 weeks post-CFA injection, pain aversion within 2 weeks, depression within 4 weeks, and cognitive impairments at 2-4 weeks. Key mechanistic findings identified heightened neuronal excitability, enhanced excitatory synaptic transmission, and neuroinflammation in the anterior cingulate cortex (ACC) and amygdala as primary contributors to pain-anxiety comorbidity. Multiple neural pathways were implicated, including enhanced S1Glu→cDLSGABA, rACCGlu→thalamus, PBN→CeA, MD→BLA, IC→BLA, and AMCAMKII→MCCCAMKII pathways, with decreased vCA1→BLA and BLA→CeA activity. Pain-depression involved enhanced BLA→ACC pathways, while pain-cognition comorbidity showed enhanced IL→LC but decreased vCA1→IL pathways. Additional mechanisms included inflammation, oxidative stress, apoptosis, ferroptosis, and gut-brain axis dysfunction. Clinical relevance: Understanding these neurobiological mechanisms may inform multimodal treatment approaches, including acupuncture targeting neuroinflammation and neural pathway modulation in chronic inflammatory pain conditions.