Inclusion Criteria:  Age > 18 years Written informed consent Indolent Multiple myeloma or monoclonal gammopathy of unknown significance (MGUS) with monoclonal IgG component Active cryoglobulinemia vasculitis defined by positive type I IgG cryoglobulinemia and a clinically active cryoglobulinemia with skin, joint, renal, and/or peripheral involvement, Treated naïve or relapsers type I cryoglobulinemia patients Affiliated to National French social security system  Contraception :  Male participants : A male participant must agree to use a highly effective method of contraception during the participation period and for at least 5 months after the last dose of study treatment and refrain from donating sperm during this period. Female participants : A female participant is eligible to participate if she is not pregnant, not breastfeeding, and with at least one of the following conditions: Not a female of childbearing potential (FCBP), OR A FCBP who must have a negative serum or urine pregnancy test with a sensitivity of at least 25 mIU/mL within 24 hours of starting study medication and must apply a highly effective method of contraception during the participation period and for at least 5 months after the last dose of study treatment and refrain from donating oocyte during this period HIV negative serology; negative HBs Ag test; HCV negative serology and/or negative HCV RNA if positive HCV serology  Exclusion Criteria:  Patient with a vasculitis unrelated to cryoglobulinemia Patient with non-active cryoglobulinemia vasculitis, Patient with diagnosis of multiple myeloma Patient treated with immunosuppressant (e.g alkylating agent, Rituximab, chemotherapy for plasma-cell neoplasms) introduced or increased in the month prior to the inclusion, Live vaccines within 30 days prior to baseline or concurrently with Isatuximab Infection requiring hospitalization and/or use of parenteral (IV or IM) antibiotics (antibacterials, antivirals, anti-fungals, or anti-parasitic agents) within 60 days of Day 0. Active tuberculosis HIV positive, positive Ag HbS, positive HCV RNA Any clinically significant, uncontrolled medical conditions that, in the Investigator's opinion, would expose excessive risk to the patient or may interfere with compliance or interpretation of the study results. Hypersensitivity or history of intolerance to steroids, mannitol, pregelatinized starch, sodium stearyl fumarate, histidine (as base and hydrochloride salt), arginine hydrochloride, poloxamer 188, sucrose or any of the other components of study therapy that are not amenable to premedication with steroids and H2 blockers or would prohibit further treatment with these agents. Hypersensitivity to the active substances (isatuximab and premedication) or to any of their excipients Received any investigational drug within 14 days prior to inclusion or within 5 half-lives of the investigational drug, whichever is longer. Participation in another interventional study or being in the exclusion period at the end of a previous study.  Vulnerable populations  pregnant or breastfeeding women Persons deprived of liberty by judicial or administrative decision Persons under psychiatric care without their consent Adults subject to a legal protection measure Persons unable to express their consent Neutrophils < 1000/mm3 Platelets < 75000/mm3