Localized Immunoglobulin Light-Chain Amyloidosis of the Ulnar Nerve

Amyloidosis is a disorder caused by extracellular tissue deposition of insoluble fibrils. Amyloidosis can be divided into systemic or localized disease. Primary systemic amyloidosis is a multisystem disease caused by the deposition of amyloid in various tissues. Localized amyloidosis has different characteristics than those of systemic amyloidosis. In this paper, we present the case of a middle-aged woman who presented with worsening ulnar nerve palsy. Electrophysiological examination and MRI indicated a tumor surrounding the ulnar nerve in the forearm. However, the operative findings revealed that ulnar nerve fascicles were replaced with a yellow tissue, which was diagnosed as amyloid light-chain λ amyloidosis, based on histopathological examination. Systemic amyloidosis was ruled out after the screening examinations. This paper is the first report of the ulnar nerve as the sole site of localized immunoglobulin light-chain amyloidosis manifestation.