Circulating anticoagulant against factor XI in psoriasis.

A 56 year old white man with psoriasis without serologic evidence of systemic lupus erythematosus was found to have a circulating anticoagulant against Factor XI with a low activity of Factor IX which could not be fully explained. The activity of the circulating anticoagulant was not potentiated on incubation after addition of normal plasma and it was still persisting after 15 months despite periodic treatment with methotrexate and topical steroid creams. This acquired anticoagulant neither protected the patient from myocardial infarction nor produced any bleeding complications.