Hyperviscosity encephalopathy in suspected polycythemia vera at high altitude: a case report

Polycythemia vera (PV) is a JAK2-associated clonal myeloproliferative neoplasm characterized by erythroid hyperplasia. To the best of our knowledge, this is the first reported case of acute hyper-viscosity encephalopathy as the initial manifestation of suspected PV in a resident of extreme high altitude-a diagnosis frequently mistaken for altitude-induced secondary polycythemia in this population.

A 37-year-old Tibetan man, lifelong resident at 4,100 m, presented with acute encephalopathy characterized by altered consciousness, gait ataxia, and headache. Neurological examination confirmed higher cortical dysfunction. Laboratory studies showed marked erythrocytosis (hemoglobin 229 g/L, hematocrit 77.4%) with paradoxically suppressed serum erythropoietin (EPO, 1.2 mIU/mL). Brain magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) revealed acute bilateral frontoparietal and centrum semiovale diffusion-restricted lesions. Neurological symptoms resolved rapidly after osmotic therapy for intracranial hypertension. These findings were consistent with suspected PV based on WHO diagnostic criteria.

This case suggests that acute infection may trigger life-threatening hyper-viscosity syndrome in suspected PV at extreme altitudes. EPO assessment and JAK2 mutational analysis are recommended to be included in the diagnostic algorithm to distinguish malignant PV clones from compensatory polycythemia and to prevent catastrophic neurological outcomes in high-altitude residents.