Acquired factor VIII inhibitor in a patient with multiple sclerosis treated with interferon β-1a

Acquired Factor VIII inhibitor is a rare acquired clotting disorder which has been seen in the setting of particular medications, autoimmune disease, and malignancy. Reports of this disorder in patients receiving immunomodulatory therapies for multiple sclerosis are rare. We present a case of a 48 year-old woman with likely development of acquired Factor VIII inhibitor in the setting of interferon beta monotherapy for multiple sclerosis, and discuss the pathogenesis of this disorder which involves shifts in helper T cell populations and increased production of immunoglobulins.