ACUTE ENCEPHALOPATHY ASSOCIATED WITH THE USE OF INTRAVENOUS IMMUNOGLOBULIN. REPORT OF ONE CASE Adverse reactions to intravenous immunoglobulin (ivIg) therapy, such as anaphylaxis, acute encephalopathy, aseptic meningitis, or thrombotic phenomena are uncommon. We report a 58-year-old man with hypertension presenting with muscle weakness which led to paraparesia and respiratory failure. With the diagnosis of Guillain-Barré syndrome (GBS), he was treated with ivIg. He developed an acute encephalopathy few hours after the administration of ivIg, with a decreased level of consciousness and agitation. A CT scan revealed moderate and diffuse brain edema.  Encephalopathy resolved 96 hours after ivIg withdrawal and use of plasma exchange. A CT scan performed seven days after showed the resolution of brain edema.