[Acquired Willebrand factor deficiency associated with monoclonal IgG kappa gammapathy. Presence of an inhibitor of ristocetin co-factor (author's transl)].

An 85-year-old woman without personal history of haemorrhages was found to have qualitative and quantitative deficiency of Factor VIII persisting at least 6 months. Asymptomatic monoclonal IgG kappa gammopathy was also discovered in the same patient, together with a circulating inhibitor of ristocetin co-factor. The fact that the inhibitory effect was reduced after the patient's serum IgG's were bound to staphylococcal protein A suggests that the inhibitor belonged to that category of immunoglobulins, although the authors were unable to detect it after elution.