Posterior Reversible Encephalopathy Syndrome as a Complication of Essential Thrombocythemia: A Case Report and Literature Review.

Posterior reversible encephalopathy syndrome (PRES) is a well-defined clinicoradiological syndrome that can arise in various clinical settings, most commonly in association with hypertensive states. However, less typical causes, including hematologic disorders, have also been reported. A 47-year-old male with CALR-mutated essential thrombocythemia (ET) on chronic aspirin therapy developed progressive headache, drowsiness, nausea, and blindness. Workup revealed worsening thrombocytosis (1,250 × 10⁹/L) with unremarkable blood pressure, craniocervical AngioTac, and systemic assessment. PRES secondary to ET exacerbation was suspected. Hydroxyurea was initiated, leading to platelet reduction and symptom improvement. Brain MRI showed bilateral parieto-occipital Fluid-Attenuated Inversion Recovery (FLAIR) hyperintensities. At four months, only mild visual disturbances persisted, with follow-up MRI showing near-complete resolution. ET decompensation may trigger PRES even with normal blood pressure, highlighting the importance of platelet monitoring to prevent complications. All reported cases involved middle-aged males with severe thrombocytosis (>700 × 10⁹/L) and symptom resolution following ET treatment and platelet reduction.