Inclusion Criteria:  Patients with sciatica of disc origin (radio-clinical concordance on MRI or CT) postero-lateral Duration of evolution greater than 3 weeks despite analgesic / AINS treatment, and less than 3 months EVA sciatica pain > 4/10 Oswestry 30 at inclusion Patient aged 18 years and older Patient affiliated to a social security scheme Patient able to understand the protocol and having signed an informed consent Patient with an indication for corticosteroid infiltration in the context of their pathology  Criteria for non-inclusion  Signs or risks of infection, in particular signs of virosis Poor local skin condition Anticoagulation with VKA or anti-Xa, or haemorrhagic disease Neurological deficit < 3/5 or signs of cauda equina irritation Tarlov's cyst or low dural sac below week 4 Hypersensitivity to Lidocaine, Dexamethasone, or any of its excipients Infiltration of the spine within the previous 3 months Patient with bilateral sciatica Patient with sciatica of osteoarthritic origin Patients with chronic respiratory insufficiency Pregnant or breastfeeding women or women refusing effective contraception until M3 Patient deprived of liberty or under legal protection (guardianship or curatorship) Patient under court protection Patients participating in another clinical research protocol involving a drug or medical device Patients unable to follow the protocol, as judged by the investigator Patient refusing to participate in the study Patient with clinically narrowed lumbar canal Patient with polyneuropathy or myelopathy Patient with sequelae of neuropathic pain