Inclusion Criteria:  Medical History :  severe and prolonged rotatory vertigo; acute onset, subacute, within 3 days; nausea ; imbalance.  Physical examination :  spontaneous nystagmus beating towards the healthy ear (fast phase); no evidence of central vestibular lesion; Head impulse test abnormal, at least for the lateral semicircular canal (in some cases, the sign is only detectable for the 2 vertical semicircular canals with specific equipment, mostly not available in current practice); areflexia or hyporeflexia (asymetry > 70% calculated according to the classical Jongkees formula [slow phase velocity of the nystagmus in response to caloric stimulation at (right at 30°C + right at 44°C) - ( left at 30°C + left at 44°C ) / (right 30°C + left 30°C + right 44°C + left at 44°C) x 100], in the caloric test (10 cc in 20 s, at 30 and 44° C)  Exclusion Criteria:  history of vestibular disorders other than benign paroxysmal positionning vertigo (BPPV); symptoms lasting more than 3 days; cochlear symptoms (deafness before, during or after vertigo); central oculomotor dysfunction; central vestibular dysfunction; signs of brain dysfunction (e.g. epilepsy); MRI (if done) abnormal central vestibular pathways; psychiatric disease (history of psychiatric disease); glaucoma ; acute infection (herpes simplex, herpes zoster, corneal herpes, chicken pox, tuberculosis); patients already on corticosteroids; severe diabetes (fasting blood glucose > 7 mmol/l); Severe hypertension (systolic >180; diastolic > 110); contraindications to glucocorticoids (peptic ulceration, osteoporosis confirmed by bone density tests or pathological fractures); allergy to glucocorticoids or mannitol malignant disease; cardiac disease (recent myocardial infarction, heart failure); liver dysfunction (cirrhosis) renal insufficiency; Pregnancy or breastfeeding.