Spontaneous resolution of acquired factor X deficiency in amyloidosis.

We describe the case of a 51-year-old man with systemic amyloidosis in whom factor X activity was initially 6% of the normal. Amyloidosis was responsible for congestive heart failure and a nephrotic syndrome but there was no bleeding diathesis. A 12-month trial of melphalan and prednisone failed to improve cardiac and renal dysfunction; factor X levels remained low. Eighteen months after this treatment was stopped, factor X spontaneously normalized although renal insufficiency persisted. We suggest that the possibility of a spontaneous factor X recovery must be considered when evaluating efficacy of therapeutic agents in amyloidosis.