Polycythemia and chorea.

Polycythemia vera is a sporadic myeloproliferative disorder of increased red blood cell mass affecting multiple organ systems. Associated thrombosis, hemorrhaging, and hyperviscosity commonly result in neurological manifestations, sometimes in the form of chorea and ballism. Resultant choreiform movements have been mainly described as generalized with orofaciolingual and appendicular muscle involvement, hypotonia, and hyporeflexia. Chorea has also been uncommonly reported as arising from secondary causes of polycythemia; however, the underlying pathophysiology has not been clearly elucidated. Proposed mechanisms for basal ganglia dysfunction include hypoperfusion due to venous stasis, receptor hypersensitivity in a setting of reduced catecholamine levels, and altered platelet dopamine metabolism. Magnetic resonance imaging and single-photon emission computed tomography perfusion studies have failed to reveal an anatomical or physiological basis for polycythemia vera-associated chorea, yet rare pathological examinations of deceased patients have shown signs of cerebral venous thrombosis and perivenous demyelination. Administration of neuroleptics may suppress abnormal choreiform movement; however, effective management of polycythemia vera requires serial venesections in conjunction with chemotherapy. Appropriate treatment may prolong survival to more than 10 years, although chorea may spontaneously remit, re-emerge with resurgence of disease, or continue indefinitely despite maintenance therapy.