Fluoxetine in Multiple System Atrophy Patients

Inclusion Criteria: * Female or Male Patient with Multiple System Atrophy's disease diagnosed according to international consensus criteria (Gilman's criteria) * Patient between 30 and 80 years of age * Patient not presenting a cognitive problem that could impair the comprehension of the patient and his participation in the protocol * Patient receiving an anti-parkinsonian treatment (if applicable) at a stable dose for at least 2 months before entering the study, and with the expectation that the treatment will remain unchanged throughout the course of the patients participation in the trial * Patient receiving a symptomatic treatment of autonomic disorders (if applicable) at a stable dose for at least 2 months before entering the study, and with the expectation that the treatment will remain unchanged throughout the course of the patient participation in the trial * Signed informed consent obtained * Patient eligible for social security (specific requirement under French law) Exclusion Criteria: * Patient presenting major swallowing problems as he will not take capsule * Patient already receiving a selective inhibitor of serotonin reuptake or other antidepressant, or patient having received one in the 3 months preceding the start of the study * Patient with major depressive syndrome for which the investigator considers that the indication of an antidepressant seems essential * Bedridden patient or confined to a wheelchair during the whole day * Patient with severe hyponatremia * Patient with another Parkinsonian's syndrome that the Multiple System Atrophy (type of atypical Parkinson's disease, progressive supra nuclear paralysis, cortico-basal degeneration) * Patient with dementia * Patient with a Mini-Mental State Exam score \< 24 * Patient unable to understand the protocol or another endpoint or to consider the clinical trial's process * Patient with a chronic disease affecting the development or assessment of the patient during the trial * Patient receiving concomitant medications which could affect the evaluation of outcome measures (e.g. neuroleptics for the assessment of parkinsonian symptoms, vasodilators for the assessment of orthostatic hypotension, sedative drugs prescribed during the day for the assessment of the daytime sleepiness, of apathy or of fatigue) * Patient with absolute or relative contraindications of Fluoxetine (hypersensitivity to Fluoxetine, patient with a history of epilepsy, of manic state, of severe hepatic or renal impairment, of skin bleeding, of severe heart, of uncontrolled diabete, patient treated by selective or non selective IMAO) * Person who are: wards of the state or prisoners (requirement under french law) * Patient pregnant or at risk of same, nursing mother