AIns (insulin) type amyloidosis in a kidney transplant candidate with a newly identified monoclonal gammopathy.

Background: Amyloidosis is a heterogeneous group of disorders with 42 types of amyloidogenic proteins currently described. The most common forms include AL (immunoglobulin light chain), ATTR (transthyretin), and AA ([Apo] serum amyloid A). Beyond routine Congo red staining, amyloid typing is essential to ensure the appropriate diagnosis and clinical management of patients with amyloidosis.

Purpose: In this report, we discuss the utility of proteomics-based amyloid typing in the setting of a patient with a newly identified monoclonal gammopathy (IgG kappa) discovered during an evaluation for kidney transplantation. This case highlights the value of recognizing non-AL amyloid proteins.

Methods: Amyloid protein identification by liquid chromatography tandem mass spectrometry (LC-MS/MS) was performed on an abdominal subcutaneous fat aspirate (SFA) from the patient.

Results: The bone marrow biopsy demonstrated involvement by plasma cell myeloma (15% kappa monotypic plasma cells). Although a Congo red stain on the biopsy showed no amyloid deposition, amyloid was identified in the concurrent SFA. Instead of AL amyloid, LC-MS/MS demonstrated AIns (insulin) type amyloid, which was confirmed to be related to the patient's subcutaneous insulin injections. With this information, the patient was diagnosed with SMM and remained a viable candidate for kidney transplantation.

Conclusions: Proteomics-based amyloid typing allows sensitive and specific identification of both common and rare amyloid types. Amyloid typing by this method ensures appropriate clinical management of patients with both systemic and localized amyloidosis.