Turner and Wills describe a patient with the Miller Fisher syndrome treated with intravenous immunoglobulin (IVIg), who developed transient confusion and reversible blindness.1 The authors state that the bilateral occipital lobe changes seen on brain MRI were secondary to cerebral infarction. They postulate that this may have occurred as a result of hyperviscosity, although at the time of the event the plasma viscosity was only marginally raised at 1.85 cP (normal range 1.5—1.72 cP). The images seem to show relative sparing of the cortex, which would be rather unusual if the cause was indeed an arterial infarct as would be expected if the mechanism was hyperviscosity induced thromboembolism.2 The authors do not specifically mention that they excluded a cerebral venous sinus …

Dr B Turner nnxbt{at}nnn1.nottingham.ac.uk