Lethal capillary leak syndrome after a single administration of interferon beta-1b.

Interferon beta-1b (IFNbeta-1b) is a potent immunomodulatory drug in the treatment of MS. We report a lethal capillary leak syndrome after the administration of IFNbeta-1b in a patient with disseminated white matter disease, monoclonal gammopathy, and acquired C1 inhibitor (C1-INH) deficiency. IFNbeta-1b may cause a transient release of proinflammatory cytokines finally resulting in an uninhibited activation of the complement cascade in patients with C1-INH deficiency.