Chronic inflammation underpins the pathogenesis of both rheumatoid arthritis (RA) and neurodegenerative conditions such as Alzheimer’s disease (AD). This narrative review explores the role of C-reactive protein (CRP), particularly its monomeric form (mCRP), as a central molecular link connecting systemic autoimmune inflammation with neuroinflammatory and vascular pathology. In RA, fibroblast-like synoviocytes (FLSs) are activated by CRP through CD32/CD64-mediated signaling, triggering proinflammatory cascades involving NF-κB and p38 MAPK. Recent studies have highlighted that locally synthesized CRP within the synovium may convert to mCRP, amplifying inflammation and tissue damage. Beyond RA, mCRP has been identified within amyloid-beta (Aβ) plaques in AD brains, suggesting a direct role in neurodegenerative pathology. Experimental models also demonstrate that mCRP is upregulated in stroke-affected brain regions and associated with complement activation and blood–brain barrier (BBB) disruption, which is central to AD progression. The convergence of pathways involving IL-6, RAGE (receptor for advanced glycation end-products), and mCRP-mediated complement activation reveals a shared axis of inflammation between RA and AD. This highlights the potential of mCRP not only as a biomarker of chronic inflammation but also as a therapeutic target. Furthermore, evidence from periodontal disease and cardiovascular comorbidities highlights the systemic nature of mCRP-driven inflammation, offering insights into the mechanisms of disease overlap. This review advocates for further mechanistic studies into mCRP signaling, particularly its role at the interface of systemic and neuroinflammation, with the goal of identifying new interventional strategies for patients with RA at elevated risk of neurodegenerative and vascular complications.

Systemic inflammation plays a pivotal role in the progression of rheumatoid arthritis (RA) and its associated comorbidities, ranging from cardiovascular (CV) disease to neurodegenerative conditions such as Alzheimer’s disease (AD). This narrative review examines the molecular cross-talk linking these pathologies, with a specific focus on the distinction between pentameric C-reactive protein (pCRP) and its proinflammatory monomeric form (mCRP). We discuss evidence suggesting that mCRP is not merely a passive marker but also an active driver of endothelial dysfunction, atherosclerosis, and synovial inflammation. This review further explores the connections among inflammatory biomarkers, blood vessel integrity, and neurodegeneration, detailing how persistent cytokine elevation (IL-6, TNF-α) and vascular injury contribute to cerebral small vessel disease (cSVD) and cognitive decline, with neurofilament light chain (NfL) serving as a key biomarker of neuroaxonal injury. Additionally, we address the neurobiology of pain in RA, highlighting the mechanisms of central sensitization (CS) and neuroimmune signalling that sustain pain-independent joint swelling. This evidence indicates that understanding the dynamic connection between CRP isoforms and neuronal markers should offer new insights for risk stratification and suggests that targeting mCRP may provide a novel therapeutic avenue to mitigate both articular and extra-articular manifestations of RA.