関節リウマチにおけるBMIとインフリキシマブの効果の関連

関節リウマチにおけるBMIとインフリキシマブ（生物学的製剤、商品名レミケード）の効果の関連をみた論文を紹介します。

Klaasen R, Wijbrandts CA, Gerlag DM, Tak PP. Body mass index and clinical response to infliximab in rheumatoid arthritis. Arthritis Rheum. 2011 Feb;63(2):359-64. doi: 10.1002/art.30136.

インフリキシマブは体重1kgあたり3mg、経静脈的に投与しました。結果ですが、インフリキシマブ使用前のBMIと疾患活動度（DAS28）には、有意な関連を認めました。また、疾患活動度で調整した後でも、BMIが高い患者では疾患活動度の改善が有意に低い関連を認めました。

つまり、BMIが高い関節リウマチ患者では脂肪量が多く、脂肪組織が関節リウマチにおいて何らかの免疫調整に関わっている可能性があるといえます。

ただ、多変量解析は行っていますが、関節リウマチがより重度の患者では、インフリキシマブの効きが悪く、悪液質のことが多い（関節リウマチによる悪液質やサルコペニアでは、脂肪量が保たれていることも多い）のかもしれません。

また、同じ体重の関節リウマチ患者でも筋肉量が多いか少ないか、脂肪量が多いか少ないかで、インフリキシマブの投与量を変更しなければいけないのかもしれません。

Abstract
OBJECTIVE: Adipose tissue has immunomodulating effects in rheumatoid arthritis (RA), although the exact role is, at present, unclear. The purpose of this study was to determine whether body mass index (BMI) affects response to infliximab in RA patients investigated prospectively.

METHODS: In 89 patients with active RA, the BMI was calculated before initiation of infliximab treatment (3 mg/kg intravenously). After 16 weeks of treatment, changes in disease activity were assessed with the Disease Activity Score in 28 joints (DAS28).

RESULTS: The mean ± SD BMI was 26 ± 5 kg/m(2) (range 17-42). The BMI correlated positively with the DAS28 at baseline (r = 0.34, P = 0.001). Since selection of study patients according to DAS28 values could influence the clinical response to tumor necrosis factor (TNF) blockade due to regression to the mean because the clinical response is itself based on the change in the DAS28 values, analysis of covariance was used to correct for the baseline DAS28. A highly significant, negative association between the BMI and the absolute decrease in the DAS28 after 16 weeks (P = 0.001) was found also when adjusted for anti-citrullinated protein antibodies.

CONCLUSION: Although the infliximab dosage is based on body weight, RA patients with a high BMI responded less well to infliximab, a finding that held true when adjusted for the baseline DAS28 or anti-citrullinated protein antibody status. These results support the notion that adipose tissue may be involved in the pathophysiology of RA and could have implications for other immune-mediated inflammatory conditions treated with TNF antagonists.