plasma exchange (pe) and immunoadsorption (iA) are standard therapeutic options of immunemediated neurological disorders. This study evaluates the relation of the relative quantity of applied dose of PE and/ or IA and its achieved therapeutic effectiveness within the treated underlying neurological disorders. In a retrospective study, we evaluated data from PE and IA carried out 09/2009-06/2014 in neurological patients at the University-Hospital of Saarland, Germany. Apheresis dose was defined as the ratio of the extracorporeal treated plasma volume to the patient's plasma volume. Effectiveness was assessed through disease-specific tests and scores by the attending neurologist(s); results were classified into response or no response. 1101 apheresis (PE:238, IA:863), in 153 hospitalstays were carried out, averaged, 7.0 treatments per patients, 82% responded, 18% not. Mean applied apheresis dose per treatment was 0.91 with mean doses of 1.16 for PE and 0.81 for IA. The totally applied mean dose per stay was 5.6 (PE:5.01, IA:5.81). No correlation was seen between apheresis dosing and treatment effectiveness (PE:R2 = 0.074, IA:R2 = 0.0023). PE and IA in therapy-refractory immune-mediated neurological disorders majorly achieved a measurable severity improvementwithout correlation to the applied dose. Moreover, our data rather suggest, that effectiveness may be given with volumes below currently recommended volumes. Apheresis is an established method of removing proteins and antibodies from the blood, here of interest plasmapheresis (PE) and immunoadsorption (IA), two methods with different targeted blood components. In PE, the patient's plasma is withdrawn and replaced by fresh frozen plasma or by protein-contending solutions. In IA, the patient's plasma is passed through an adsorber, eliminating the target components. PE and/ or IA are, at least in therapy-refractory cases 1 , the standard therapeutic option for immune-mediated neurological diseases, here chronic inflammatory demyelinating polyneuropathy (CIDP) Guillain-Barré syndrome (GBS), myasthenia gravis, or multiple sclerosis. Central pathogenic elements of these immune-mediated diseases are B-lymphocytes and antibodies as directed to structures of the nervous system and are involved in the process of neuroinflammation, leading to neurological symptoms e.g the ascending paralysis or sensory deficits. So far, recommendations for relative plasma volume per patient and treatment are few and inconsistent. In our study, we exactly ask the question of a direct proportional effectiveness of PE and IA regarding response/ no response correlated to the applied apheresis dose, meaning the relative quantity of treated plasma volume. Methods Study population. All patients with study relevant immune-mediated nlogeuroical disorders and treated in the Department of Neurology at the Saarland University Medical Centre (UKS) between Sept 2009 and June 2014, were per se eligible for this study. Thereof, the therapeutic option of apheresis was considered in case of therapy failure ...

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