BackgroundPericoronary adipose tissue (PCAT) density is a biomarker of vessel inflammation, which is supposed to be increased in patients with type 2 diabetes mellitus (T2DM). However, whether the coronary inflammation revealed by this novel index could be alleviated after evolocumab treatment in T2DM remains unknown.MethodsFrom January 2020 to December 2022, consecutive T2DM patients with low-density lipoprotein cholesterol ≥ 70 mg/dL on maximally tolerated statin and taking evolocumab were prospectively included. In addition, patients with T2DM who were taking statin alone were recruited as control group. The eligible patients underwent baseline and follow-up coronary CT angiography with an interval of 48-week. To render patients with evolocumab as comparable to those controls, a propensity-score matching design was used to select the matched pairs with a 1:1 ratio. Obstructive lesion was defined as the extent of coronary artery stenosis ≥ 50%; the numbers inside the brackets were interquartile ranges.ResultsA total of 170 T2DM patients with stable chest pain were included [(mean age 64 ± 10.6 [range 40–85] years; 131 men). Among those patients, 85 were in evolocumab group and 85 were in control group. During follow-up, low-density lipoprotein cholesterol (LDL-C) level (2.02 [1.26, 2.78] vs. 3.34 [2.53, 4.14],p< 0.001), and lipoprotein(a) (12.1 [5.6, 21.8] vs. 18.9 [13.2, 27.2],p= 0.002) were reduced after evolocumab treatment. The prevalence of obstructive lesions and high-risk plaque features were significantly decreased (p< 0.05 for all). Furthermore, the calcified plaque volume were significantly increased (188.3 [115.7, 361.0] vs. 129.3 [59.5, 238.3],p= 0.015), while the noncalcified plaque volume and necrotic volume were diminished (107.5 [40.6, 180.6] vs. 125.0 [65.3, 269.7],p= 0.038; 0 [0, 4.7] vs. 0 [0, 13.4],p< 0.001, respectively). In addition, PCAT density of right coronary artery was significantly attenuated in evolocumab group (− 85.0 [− 89.0, − 82.0] vs. − 79.0 [− 83.5, − 74.0],p< 0.001). The change in the calcified plaque volume inversely correlated with achieved LDL-C level (r =  − 0.31,p< 0.001) and lipoprotein(a) level (r =  − 0.33,p< 0.001). Both the changes of noncalcified plaque volume and necrotic volume were positively correlated with achieved LDL-C level and Lp(a) (p< 0.001 for all). However, the change of PCATRCAdensity only positively correlated with achieved lipoprotein(a) level (r = 0.51,p< 0.001). Causal mediation analysis revealed Lp(a) level mediated 69.8% (p< 0.001) for the relationship between evolocumab and changes of PCATRCA.ConclusionsIn patients with T2DM, evolocumab is an effective therapy to decrease noncalcified plaque volume necrotic volume, and increase calcified plaque volume. Furthermore, evolocumab could attenuate PCAT density, at least in part, via the reduction of lipoprotein(a).Supplementary InformationThe online version contains supplementary material available at 10.1186/s12933-023-01857-w.