The multimorbidity of rheumatoid arthritis （RA） and periodontitis （PD） has drawn increasing attention， as both conditions are characterized by chronic inflammation， immune dysregulation， and progressive bone destruction. Modern research confirms that PD is a significant risk factor for RA development， and their coexistence mutually exacerbates disease progression. However， traditional Chinese medicine （TCM） currently lacks a systematic theoretical explanation for this complex multimorbid relationship. This study， based on the TCM theory of abnormal collateral， thoroughly examines the intrinsic connection between RA and PD multimorbidity， proposing "abnormal collateral as the pivot， with accumulated toxins eroding bone" as the core TCM pathogenesis. The research elucidates PD as the "origin of abnormal collateral"， where its pathogens act as toxic factors that invade the joints through collaterals， triggering RA via mechanisms such as molecular mimicry. The dynamic pathological progression of RA-PD multimorbidity can be described as follows： the displacement of Ying and Wei at the microscopic level manifests as immune hyperactivation， leading to collateral malnutrition； heat-toxins traversing collaterals induce collateral hyperactivity， resulting in pathological angiogenesis； ultimately， toxin accumulation at the pivotal abnormal collateral site erodes bone， activating the receptor activator of nuclear factor kappa-B ligand （RANKL）-receptor activator of nuclear factor kappa-B （RANK） signaling pathway-driven osteoclast differentiation. This theoretical framework innovatively integrates modern findings in oral microbiology， immune-inflammation， and bone metabolism， offering a holistic and dynamic perspective to understand the complexity of multimorbidity. Given the limited efficacy of current periodontal treatments for RA and the scarcity of reported TCM compound interventions for multimorbidity， the abnormal collateral theory proposes a systematic intervention strategy centered on "governing diseases through collaterals and regulating collaterals with herbs"， along with TCM therapeutic principles such as "unblocking， clearing， and nourishing collaterals". Potential herbal treatments for multimorbidity are also highlighted. Future research should focus on refining TCM syndrome patterns in multimorbid patients and leveraging omics technologies for deeper exploration， thereby providing a theoretical foundation and research direction for TCM in addressing complex multimorbid conditions.

The multimorbidity of rheumatoid arthritis （RA） and periodontitis （PD） has drawn increasing attention， as both conditions are characterized by chronic inflammation， immune dysregulation， and progressive bone destruction. Modern research confirms that PD is a significant risk factor for RA development， and their coexistence mutually exacerbates disease progression. However， traditional Chinese medicine （TCM） currently lacks a systematic theoretical explanation for this complex multimorbid relationship. This study， based on the TCM theory of abnormal collateral， thoroughly examines the intrinsic connection between RA and PD multimorbidity， proposing "abnormal collateral as the pivot， with accumulated toxins eroding bone" as the core TCM pathogenesis. The research elucidates PD as the "origin of abnormal collateral"， where its pathogens act as toxic factors that invade the joints through collaterals， triggering RA via mechanisms such as molecular mimicry. The dynamic pathological progression of RA-PD multimorbidity can be described as follows： the displacement of Ying and Wei at the microscopic level manifests as immune hyperactivation， leading to collateral malnutrition； heat-toxins traversing collaterals induce collateral hyperactivity， resulting in pathological angiogenesis； ultimately， toxin accumulation at the pivotal abnormal collateral site erodes bone， activating the receptor activator of nuclear factor kappa-B ligand （RANKL）-receptor activator of nuclear factor kappa-B （RANK） signaling pathway-driven osteoclast differentiation. This theoretical framework innovatively integrates modern findings in oral microbiology， immune-inflammation， and bone metabolism， offering a holistic and dynamic perspective to understand the complexity of multimorbidity. Given the limited efficacy of current periodontal treatments for RA and the scarcity of reported TCM compound interventions for multimorbidity， the abnormal collateral theory proposes a systematic intervention strategy centered on "governing diseases through collaterals and regulating collaterals with herbs"， along with TCM therapeutic principles such as "unblocking， clearing， and nourishing collaterals". Potential herbal treatments for multimorbidity are also highlighted. Future research should focus on refining TCM syndrome patterns in multimorbid patients and leveraging omics technologies for deeper exploration， thereby providing a theoretical foundation and research direction for TCM in addressing complex multimorbid conditions.