SAT-544 Insulin Amyloidoma: A Rare Complication of Long-Term Therapy

Abstract Disclosure: Z. Ahmed: None. S. Anderson: None. T. Patel: None. T. Porter: None. Introduction: Insulin amyloidoma, or insulin-derived amyloidosis, is a rare but significant complication of long-term insulin therapy. It is caused by localized deposition of amyloid fibrils at injection sites, impairing insulin absorption and glycemic control [1]. Clinical presentation often mimics neoplastic or inflammatory lesions, making awareness and timely diagnosis essential. Differential diagnoses include lipohypertrophy, lipoma, and neoplasms, emphasizing the need for biopsy confirmation [2,3]. Case Presentation: A 59-year-old male with type 1 diabetes for 47 years reported a painless, slowly enlarging left abdominal mass first noticed in 2017, with rapid growth from 2022 onward. His insulin regimen included U200 lispro delivered via a tubeless, wearable insulin pump since 2018, following prior use of U500 and glargine injections. In November 2023, biopsy revealed eosinophilic, amorphous material consistent with amyloidoma, confirmed by Congo red staining and apple-green birefringence under polarized light. Histological analysis identified kappa-restricted plasma cells, though bone marrow biopsy showed no plasma cell neoplasm. PET imaging demonstrated FDG uptake limited to the abdominal wall mass, excluding systemic involvement. Laboratory studies including beta-2 microglobulin and monoclonal protein were unremarkable. Surgical excision in March 2024 removed a 45 x 17 cm mass, and pathology confirmed insulin amyloidoma. Postoperatively, the patient developed a seroma that resolved after drainage. Glycemic control improved after avoiding this site for insulin pump insertion. Conclusion: This case highlights the importance of clinical suspicion for insulin amyloidoma in diabetic patients with persistent subcutaneous masses at injection sites. Accurate diagnosis through early recognition of symptoms and evaluation with biopsy and histology can prevent unnecessary oncologic interventions and improve glycemic outcomes. Management involves avoiding further injections at the site and considering surgical excision for symptomatic relief or improved insulin absorption [3]. References: 1. Nakamura M, et al. Extreme Adhesion Activity of Amyloid Fibrils Induces Subcutaneous Insulin Resistance. Diabetes. 2019;68(3):609-616. 2. Ramani NS, et al. AIns (Insulin) Type Amyloidoma Diagnosed by Fine-Needle Aspiration. Diagnostic Cytopathology. 2024;52(5):E116-E119. 3. Yumlu S, et al. Localized Insulin-Derived Amyloidosis in Diabetes Mellitus. Human Pathology. 2009;40(11):1655-60. Presentation: Saturday, July 12, 2025