| Summary: | Systemic amyloid light-chain amyloidosis is a protein misfolding disorder characterized by extracellular deposition of amyloid fibrils derived from abnormal clonal immunoglobulin light chains in various organ systems. While amyloid light-chain amyloidosis is known to cause neuropathy when it involves the peripheral nervous system, deposition within peripheral nerve sheath tumors has not been previously reported. A 68-year-old man with a history of systemic amyloid light-chain amyloidosis with cardiac and renal involvement presented with a painful mass in the lower third of the leg. Imaging was consistent with a peripheral nerve sheath tumor. Pathologic evaluation demonstrated a schwannoma, which unusually contained prominent amyloid deposition, subsequently demonstrated to be of amyloid light-chain-type by mass spectrometry-based proteomic analysis. Amyloid light-chain deposition has been characterized in different organs and tissues, including neurosurgical specimens such as peripheral nerve. This case highlights a new finding of amyloid light-chain deposition in a schwannoma, which likely resulted from gradual amyloid light-chain deposition in a slow-growing schwannoma prior to treatment of systemic amyloid light-chain amyloidosis. Treatment protocols vary dramatically. Therefore, it is crucial to establish the correct amyloid type as well as to distinguish localized from systemic disease.
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