[Posterior reversible encephalopathy syndrome caused by long-term administration of Azathioprine: a case report].

A 57-year-old woman, who had been taking azathioprine (AZP) for systemic sclerosis and interstitial pneumonia over 16 years, presented with right hemiparesis and paresthesia. On admission, brain MRI diffusion-weighted imaging (DWI) demonstrated high-signal-intensity lesions in the right frontal lobe. Although the symptoms had disappeared quickly, brain MRI on the 7th day revealed that these lesions had spread to the left cerebellar hemisphere and the right fronto-parietal lobes, appearing as high signal intensity lesions on ADC map. On the basis of the MRI imaging and clinical courses, posterior reversible encephalopathy syndrome (PRES) caused by AZP was suspected, and brain MRI revealed the immediate improvement of the lesions after the AZP discontinuation. There have been a few reports of PRES caused by AZP, all of which occurred within one month after administration. It is noteworthy in considering differential diagnosis that PRES can also occur during long-term administration of AZP.