The Posterior Reversible Encephalopathy Syndrome (PRES), is a rare entity that is associated with hypertension, autoimmune diseases and cancer drugs. We describe a 62 year old female patient with myasthenic crisis that following treatment with immunoglobulin G who presents neurological impairment, with initial MRI lesions suggestive of PRES, which were confirmed in control imaging. This entity should be considered in patients presenting with focal neurological impairment following the use of immunoglobulin.