Giant Cell Arteritis: Comparison Between Two Standardized Corticosteroids Tapering

Inclusion Criteria: * Age ≥ 50 years * Patient with temporal arteritis giant cell match 2 of the 4 criteria of the American College of Rheumatology (ACR) that given : * a temporal artery biopsy compatible with a diagnosis of CAG or * an abdominal thoracic aortitis diagnosed by Angio CT, MR angiography or PET scanner or * Echo Doppler compatible with a diagnosis of CAG * Oral corticosteroid treatment started up to 14 days, the initial dose is less or equal to 1 mg / Kg * Patient wo has given its written consent Patient affiliated with a social security Exclusion Criteria: Subjects checking one of the criteria for non-inclusion may be eligible to participate in the research. These criteria may include: * Early treatment of CAG disease with a dose\> 1 mg / kg whatever the duration * Corticosteroids already started over 14 days * Giant arteritis cell on relapse * dementia syndrome * No compliant patient * Patients who live more than 150 km from the investigation center * Person under judicial protection, guardianship * Hypersensitivity to prednisone or any of its excipients * Infection requiring an systemic treatment * Evolutive viroses (Hepatitis, Herpes, varicella-zoster virus) * Immunization with live vaccines / mitigated during the 8 weeks preceding inclusion * Pregnancy, breastfeeding women or women of childbearing potential not using contraception