Localized insulin‐derived amyloidosis: A potential pitfall in the diagnosis of systemic amyloidosis by fat aspirate
Authors: Anita D'souza, Jason D. Theis, Julie A. Vrana, Francis Buadi, Angela Dispenzieri, Ahmet Dogan
Journal: American Journal of Hematology (2012)

Accurate amyloid subtyping is critical after diagnosing amyloidosis as treatment can vary from observation to chemotherapy or organ transplantation depending on the subtype. Localized amyloidosis at insulin injection sites (AIns) is a known complication of insulin [1-3]. We present three cases of insidious AIns that were referred as systemic amyloidosis. Using mass spectrometry (MS), we analyzed the amyloid proteome in these patients. One half of the fat aspirate specimen was processed in RPMI media containing 10 U/ml heparin sulfate and collected on a polyester filter (Netwell; Corning). The spicules were washed with media and erythrocyte lysis buffer (Buffer EL; Qiagen). The tissue was solubilized, de-lipidated, lyophilized, and disrupted by sonication in 0.1 M TRIS pH 8. The sample was digested in trypsin (Promega) and subjected to nano-flow liquid chromatography electrospray tandem MS. The data were interrogated in the Swiss-Protein database using Mascot, Seaquest and X! Tandem search algorithms. The results were assigned probability scores in Scaffold (Proteome Software, OR). Protein identifications were accepted if established with at least 95% probability, at 90% confidence. Using spectral counting approach, proteins with greater number of spectra were considered to be present at higher concentrations. Patient 1, a 79-year-old female with Type 1 diabetes for 46 years, on recombinant insulin, presented to Cardiology with exertional dyspnea. An electrocardiogram showed left axis deviation, right bundle branch block, and first-degree atrioventricular block; echocardiogram showed concentric left ventricular hypertrophy with an interventricular septum measuring 15 mm. Her N-terminal prohormone of brain natriuretic peptide (NT-pro BNP) was 2,178 pg/ml (10–244 pg/ml). This prompted a suspicion for infiltrative cardiomyopathy. She had chronic kidney disease without proteinuria and tingling in hands and feet. In the preceding 2 years, she had lost 30 lbs, and diagnosed with gastric dumping syndrome. A fat aspiration was Congo red positive. She was referred to Hematology for further management of suspected systemic amyloidosis. Incidentally, she was experiencing frequent hypoglycemic episodes over the preceding year. MS analysis of the fat aspirate specimen revealed AIns (Fig. 1, patient 1). Scaffold overview of three fat aspirates with AIns showing insulin (no. 1) in all three patients. Patient 2, a 71-year-old female with Type 1 diabetes for 60 years presented to Cardiology with exertional dyspnea and labile blood pressure. She had recurrent episodes of hypoglycemia. Echocardiogram revealed preserved ejection fraction with severe diastolic dysfunction. A cardiac MRI did not show classic gadolinium nulling seen with amyloidosis. Cardiac catheterization showed coronary atherosclerosis. Other testing revealed a creatinine of 1.2 mg/dl with microalbuminuria at 121 mg/day. She had untreated small lymphocytic lymphoma, with a monoclonal IgM lambda protein on immunofixation. Systemic immunoglobulin-derived amyloidosis was considered and an abdominal fat aspirate duly performed showed amyloid. MS analysis revealed insulin within the amyloid deposits in the abdominal fat and a diagnosis of AIns was made (Fig. 1, patient 2). Patient 3, A 52-year-old male presented to the Medicine Clinic with a 20 lbs weight loss over several months, along with nausea, emesis, and diarrhea. He had an abdominal fat aspirate performed elsewhere to evaluate for secondary amyloidosis and this was Congo red positive. He was referred to us to assess for systemic amyloidosis. He was on subcutaneous recombinant insulin for 13 years for Type 2 diabetes mellitus. Workup did not reveal a monoclonal protein or other organ involvement. A fat aspirate was repeated at our center and was Congo red negative. No definite diagnosis was made. The patient was seen 4 years later for cytopenias, at which time a bone marrow and fat aspirate were repeated. Bone marrow was normal, with no amyloidosis. The fat aspirate showed Congophilic deposits, and MS revealed recombinant insulin within these deposits (Fig. 1, patient 3). Iatrogenic insulin-derived amyloidosis, a form of localized amyloidosis, was described in 1983 [4]. Patients can develop nodular deposits at insulin injection sites [1-3]. Patients often have brittle diabetes from unpredictable release of insulin from these amyloidomas. Management involves local treatment, surgical excision of amyloidomas, and avoiding these sites to administer insulin [1-3]. None of our patients had local masses/symptoms, although two patients had hypoglycemic episodes. Because long-standing diabetics can have hypertrophic cardiomyopathy, proteinuria, peripheral, and autonomic neuropathy, symptoms and signs can be mistaken for systemic amyloidosis. Presence of monoclonal gammopathy may confound the situation. MS-based proteomic amyloid typing helped in definitive diagnosis in our patients, thus avoiding unnecessary diagnostic tests and inappropriate treatment. Anita D'Souza*, Jason D. Theis , Julie A. Vrana , Francis Buadi*, Angela Dispenzieri* , Ahmet Dogan , * Division of Hematology, Department of Internal Medicine, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota.