The clinical and blood investigation reveal the diagnosis of Polycythemia vera. The image of foot shows erythromelalgia. ERYTHROMELALGIA Characterized by burning pain and erythema. Feet > hands Males > females. Most common in middle age. It may be primary (also termed erythermalgia - Mutations in the SCN9A gene) Secondary erythromelalgia myeloproliferative disorders such as polycythemia vera and essential thrombocytosis. drugs, such as calcium channel blockers, bromocriptine, and pergolideo neuropathies connective tissue diseases such as SLE paraneoplastic syndromes. POLYCYTHEMIA VERA mutation JAK2 : replaces valine with phenylalanine (V617F), leading to constitutive kinase activation-- PV pathogenesis. CLINICAL FEATURES Isolated thrombocytosis Leukocytosis splenomegaly high hemoglobin, hematocrit, or red cell count Aquagenic pruritus : distinguish PV from other causes of erythrocytosis. Hyperviscosity -Neu rologic symptoms such as veigo, tinnitus, headache, visual distur bances, and transient ischemic attacks (TIA)