Giant cell arteritis (GCA) is a large-vessel vasculitis that typically occurs in people over the age of 50.
Corticosteroids (GC) are the cornerstone of treatment for GCA. French guidelines recommend starting at 0.7 or 1 mg/kg/day at diagnosis, depending on the occurence of ischemic complication(s). Then, it is recommended to gradually decrease their dose to achieve withdrawal in 12 to 24 months.
Despite this treatment, 47% of patients relapse. Relapses are favored by rapid reduction of corticosteroid doses and large vessel involvement at diagnosis. Fortunately, relapses are severe in only 3.3% of cases and ischemic complications are very rare. However, this contributes to prolonging the duration of corticosteroid treatment and thus the risk of cortico-induced adverse events, which have not been significantly reduced in the last 20 years. The main risk factors for the development of steroid-related complications are advanced age and cumulative steroid dose.
For this reason, the development of cortisone-sparing strategies is necessary to improve the management of patients with GCA. Thanks to major advances in the understanding of the pathophysiological mechanisms of GCA, new therapeutic targets have been discovered. For example, the efficacy of tocilizumab (TCZ), an anti-IL-6 receptor monoclonal antibody, has been demonstrated in two phase 2 trials and one phase 3 trial, leading to its approval for the management of patients requiring rapid reduction in corticosteroid doses and/or those relapsing repeatedly on prednisone \>7.5 mg/day. In recently published US guidelines, TCZ can even be used at diagnosis to reduce the need for corticosteroid therapy.5 Indeed, TCZ appears to be remarkably effective in controlling GCA activity and saves approximately 2000 mg of prednisone in cumulative dose.
At present, the place of TCZ compared to methotrexate in the therapeutic strategy is still being evaluated, notably through the METOGiA study (PHRC-N 2017), which is being conducted by our team. Inclusions for METOGiA ended in March 2023 with results expected in 2025. Outside of this study, approximately 1500 patients are currently receiving TCZ treatment for GCA (data from ROCHE-CHUGAI).
There is no doubt that TCZ treatment is effective and rather well tolerated in the elderly population, but it generates problems that are not solved to date:
* the cost (\~900€/month)
* the difficulty monitoring these patients because the biological markers usually used to monitor GCA (CRP, ESR, fibrinogen) can no longer be measured since TCZ blocks their production by the hepatocytes. Monitoring of disease activity therefore requires very careful clinical examination and the use of expensive imaging tests such as PET scans because GCA can be active despite normal ESR, CRP and fibrinogen levels. Some studies suggest that monitoring serum IL-6 may help identify patients with active disease, but this test is not readily available and the threshold above which relapse should be suspected is unclear because TCZ induces an increase in serum IL-6 levels by blocking IL-6 receptors, even in patients in remission.
* For the same reasons, infections are difficult to detect in patients treated with TCZ.
This raises the question of how to discontinue this treatment, especially since other treatments that do not interfere with CRP, ESR, or fibrinogen measurements are being evaluated.
This shows that this treatment tends to be prolonged well beyond one year when the disease is often in remission without corticosteroids. This is probably related to two factors: 1/ the fear of relapse after treatment withdrawal; 2/ the absence of a scheme for withdrawing TCZ.
The risk of relapse after stopping TCZ has been reported in several studies, in particular the long-term follow-up of phase 2 and 3 trials that demonstrated the efficacy of TCZ for the treatment of GCA. Overall, regardless of the duration of TCZ treatment, the risk of relapse is approximately 40% 6 months after the last injection of TCZ, and the risk of relapse is higher if the large arteries (aorta and its branches) are involved.
Thus, although the available data are limited, it appears that tapering rather than immediately stopping TCZ limits the risk of relapse after full withdrawal.