Extended follow-up after stopping mepolizumab in relapsing/refractory Churg-Strauss syndrome.

OBJECTIVES To report on the extended follow-up of relapsing/refractory CSS patients treated with mepolizumab with respect to relapse rates. METHODS The follow-up consisted of regular clinic visits of patients who received nine infusions of mepolizumab (750mg IV) and switched to methotrexate 0.3mg/kg for maintenance of remission. Glucocorticoids were maintained as low as possible. Disease activity was measured using the Birmingham Vasculitis Activity Score (BVAS). Disease states as remission or relapse were defined according to the EULAR/EUVAS recommendations. The serum eosinophil cationic protein (ECP) was measured regularly and concentrations were correlated with BVAS. RESULTS The follow-up of the study population under standard methotrexate maintenance therapy was extended to a median of 22 months. Three of nine patients were still in remission at the end of follow-up. During this time five major relapses in three and seven minor relapses in five out of the total nine patients were recognised. ECP levels were found to correlate stronger with the BVAS (r=0.38; p<0.0001) than other measures such as eosinophil counts. CONCLUSIONS After induction of remission with mepolizumab the majority of patients suffered relapses when switched to methotrexate maintenance therapy. These data suggest that patients with CSS may require long term treatment with mepolizumab. Future trials in CSS should use other doses or dosing intervals for patients in remission. ECP is a promising marker of disease activity in CSS.