Posterior reversible encephalopathy associated with nocturnal blood pressure non-dipping pattern

We report the case of a 70-year-old man who presented with a recent history of headache, altered mental status and sleepiness. He was known to have type II diabetes mellitus, and a mild, treated and apparently well controlled hypertension. Brain magnetic resonance imaging demonstrated extensive abnormalities in the parieto-occipital white matter, suggestive of posterior reversible encephalopathy syndrome (PRES). An extensive diagnostic evaluation did not allow the detection of any known cause of the syndrome. Twenty-four-hour non-invasive ambulatory blood pressure monitoring showed a mild to moderate hypertension, with non-dipping pattern. This case suggests that, in the context of an overnight blunted blood pressure profile, even a mild or moderate hypertension can result in cerebral vasogenic oedema, underlining the diagnostic importance of 24-h blood pressure monitoring in patients with PRES without severe hypertension or other commonly recognized causes of posterior reversible encephalopathy.