Acute deep vein thrombosis with concurrent new diagnosis of AL-amyloid-induced factor X deficiency

Acquired factor X (FX) deficiency is a rare but well-documented clinical feature of AL amyloidosis. Patients with FX deficiency can present with clinically significant bleeding diathesis due to the adsorption of circulating FX to amyloid fibrils. Here, we report an unusual case of a man in his 60s who presented with 6 months of intermittent bruising, labs demonstrating new FX deficiency, elevated free lambda light chains for underlying AL amyloidosis and concurrent new peroneal vein thrombosis. This is the first report of concurrent thrombotic complications in the setting of AL-amyloid-induced FX deficiency. We discuss the diagnostic and therapeutic conundrum of diagnosing AL amyloidosis with bruising as the leading clinical symptom and the management of acute deep vein thrombosis in the setting of FX deficiency.