Psoriasis is a chronic inflammatory condition driven by a complex interplay between heritable and microenvironmental factors. Genome-wide heritability for psoriasis (PsO) is estimated at up to 50%. Although bearing genetic susceptibility at birth, most patients will remain disease free for years until an exposomal trigger activates the immunological pathway that leads to the first disease flare. In rare patients, the first flare is an isolated event, but in most patients it will evolve into a chronically relapsing-remitting disease characterized by lasting lesions and recurrent flares. Primary objective is to compare efficacy of bimekizumab versus topical corticosteroids on psoriasis clinical disease activity, assessed by PGA, at week 16 and week 24. Patients will be randomized 1:1 to receive either 320mg bimekizumab at weeks 0 (W0), W4, W8 and W12, or clobetasol ointment for 2 to 4 weeks until complete clearance of the lesion. After a maximum of 4 weeks topical clobetasol will be applied twice weekly on the site of lesion until week 16 then stopped. Patients will not receive active treatment between week 16-24. Between week 24-96 patients that flare can receive continuous topical clobetasol if needed. These patients will be considered non-responders at subsequent timepoints for the main analysis. If the patients worsen their psoriasis under the treatments given during the study and progress to moderate or severe psoriasis (PASI 10 and above) they will end their participation to the study to receive a treatment adapted to the new severity of their psoriasis. The patients will be referred to their dermatologist to receive the actual standard of care adapted to their new condition. During the study, the following assessments will be performed and samples will be collected