Acquired factor X deficiency associated with atypical AL-amyloidosis.

We herein describe the case of a 77-year-old woman with acquired factor X deficiency that was likely caused by atypical amyloidosis. The patient developed severe gastrointestinal bleeding as a result of a significant decrease of factor X activity. Neither proteinuria nor diarrhea was observed as an initial manifestation. Although a bone marrow examination revealed direct fast scarlet-positive extracellular deposits, they did not exhibit red-to-green dichroism under polarized light. Immunofluorescence microscopy showed that the fibrillar proteins were positive for CD138 but negative for β2-microglobulin or amyloid A antibodies. These atypical pathological features of immunoglobulin light chain-amyloidosis in this patient might be related to its unique clinical presentation.