Multiple reports have employed angiographic changes as important indices for evaluating therapeutic effect, but the overall conditions of vascular progression remain obscure [14, 15]. According to the present study, about one third of patients with TA suffered AVD with the median follow-up of 14 months. The most common AVD type was aggravated vascular stenosis in the original lesioned locations, while new lesions were relatively less. The limb arteries were the most vulnerable locations, although the harm arising from limb artery lesions is likely to be less than that of critical arteries that govern vital organs such as the heart, brain, or kidneys, which could increase the likelihood of serious cerebrovascular adverse events and magnify the risk of mortality [4]. Considering the difference in vascular structure and locations between limb arteries and arteries supplying vital organs, hemodynamics such as sheer press and turbulent flow might be another critical issue resulting in aggravated vascular findings, which warrants further investigation. However, the choice of therapeutic strategy should be based on end-organ perfusion for the moment [16].
Assessment and intervention of inflammation are important in patients with TA [17]. ESR and CRP, together with SUVmax in PET-CT, increased in the active disease status, which is consistent with previous findings [13]. However, inflammatory markers at the baseline, including ESR, IL-6, C3, and IL-8, did not predict AVD. Disease remission after 6 months of treatment significantly improved outcomes, indicating that active, early, and successful intervention to control inflammation and disease activity are crucial in patients with TA.
Interestingly, C4 and CRP were related to angiographic aggravation. The complement system is tightly correlated with autoimmune diseases, especially vasculitis [18, 19]. In TA, complement components, such as complement 4-binding protein and C3 [20, 21], can be used as biomarkers to monitor disease activity. In the present study, C4 was a risk factor for progression in vascular imaging, indicating that complement activation might be involved in the pathogenesis of TA. Although it was not an independent risk factor, which might be due to the limited sample size or to the confined function of C4 in complement activation, its valuable role in inducing vascular deterioration deserves further investigation.
CRP has been used as an acute phase protein to evaluate disease activity in TA during follow-up [20, 22, 23]. In the present study, CRP was found to be a prognostic factor for AVD. Comarmond et al. found that CRP, together with the male sex and carotidynia, was an independent risk factor for disease relapse [4], which is consistent with the result of present study since inflammation recrudescence is the essence of disease relapse and failure to alleviate disease activity might result in AVD. Moreover, the value of CRP instead of ESR or IL-6 in predicting AVD, also implied that CRP might be involved in the pathogenesis of TA in a deeper level from the perspective of molecular mechanisms, although the function of CRP in inflammation remains unknown largely yet [24].
Anti-inflammatory therapy is an art, especially anti-cytokine treatment, which partially interrupts vascular progress [25]. In the present study, we found that the patients in the AVD group were prescribed with more active intervention such as the usage of IL-6R and TNF-a antibodies. Previous investigations have shown that IL-6R antibody is effective for the treatment of refractory TA, and is better than cyclophosphamide [22, 23]. However, we found that some specific intervention such as IL-6R antibody failed to completely block the AVD currently, possibly because the disease condition in the progressive group was more severe, considering their younger age, higher C4, and resistance to active disease mitigation. Thus, more aggressive treatment strategies should be encouraged to obtain disease remission in the early stage of 6 months’ treatment, regardless of the drug types.
Different from giant cell arteritis, TA usually starts at a young age [26]. In the present study, we found that younger age could further increase the risk of vascular poor prognosis, which is consistent with a previous report that IL-17 and the relapse rate decrease in patients with TA over the age of 40 years [27]. This might be because of immune aging and the abnormal differentiation of inflammatory cells, such as T-helper 17 cells, in elderly patients [27, 28]. Further investigations are needed to clarify the exact mechanisms. However, the claim that younger patients should be given active and effective intervention at early stage is affirmative.
The nomogram developed based on the prognostic factors was reliable not only in general new patients but in extreme conditions where patients received effective treatments and achieved therapeutic effects. Thus, the nomogram based on earlier characteristics of patients would be a useful tool to predict AVD in TA, implying the poor prognosis in the future. More precise intervention could be prescribed to obtain better prognosis according to hazard ratios obtained from the nomogram.
The present study has several limitations. First, the result has not been validated in TA patients from other cohorts. Second, the follow-up period of the validation was restricted, despite the agreement between predictions and observations within 2 years. Third, the present study focused on the AVD at the whole level, further analysis of new lesions and different extent and locations of AVD could be performed dynamically based on the Angiographic Scores System created by Enrico Tombetti et al. [29]. Moreover, the relationship between AVD and different long-term prognosis of TA warrants further investigated.
In conclusion, 29.4% of patients in TA suffered AVD, which manifested as vascular stenosis in limb arteries mainly. Successful disease remission at 6 months, lower CRP (CRP £ 26.7 mg/L), and higher age were protective factors for AVD in TA, on which the nomogram based provided a useful tool to predict AVD. Early and active intervention is important to reduce AVD, especially for young patients.