A 22-year-old woman gradually developed depression, dementia, and chor
ea over an 8-month period. She fulfilled the criteria for the primary
antiphospholipid antibody syndrome but not those for systemic lupus er
ythematosus. Her chorea and neurobehavioral deficits responded favorab
ly to a regimen of prednisone, hydroxychloroquine, and aspirin. This a
ppears to be the first report of a patient with a lupus anticoagulant
and reversible dementia. The response to immunosuppressive therapy imp
lies an antibody-mediated condition similar to Sydenham's chorea.