Evaluation of Fluid Retention Due to Superpotent Topical Corticosteroid

Inclusion Criteria: * Patient with age higher than 18 * Patient with bullous pemphigoid, * Patient treated by local corticosteroid therapy (clobetasol propionate cream) but not yet processed or for less than 48 hours, * Signed informed consent. * Patient affiliated to Social Security Regimen * Effective contraception in women of childbearing age (for postmenopausal women, confirmatory diagnosis of menopause will be collected) Exclusion Criteria: * Concomitant treatment with corticosteroids * Recent introduction or recent (\<6 weeks) treatment with diuretics, angiotensin-converting enzyme, receptor antagonist or anti-angiotensin renin (aliskiren) * contraindication to the use of Clobetasol propionate (DERMOVAL and CLARELUX) * Patient on salt diet (\<or = to 5 g / d) * Patients carry a defibrillator or a pace maker * Amputated Patient * Pregnant and lactating * Patient with Urinary Incontinency * Recent heart decompensation in the last 6 weeks * known Nephrotic Syndrome * known or Severe hepatic impairment * Hypoalbuminaemia less than 20 g / l