[Amyloid from insulin treatment: a pitfall for the pathologist and the diabetologist]

Biopsies from six diabetic patients with subcutaneous amyloid deposits formed by injected insulin have been sent to our laboratory during the last year. In all but one of the six patients a subcutaneous adipose tissue biopsy was taken due to suspicion of systemic amyloidosis. Four of these patients had renal insufficiency, with monoclonal gammopathy of undetermined significance (MGUS) in three while the fifth had heredity for transthyretin amyloidosis. In the sixth patient a biopsy was taken due to subcutaneous nodules at insulin injection sites. In all biopsies, large amounts of amyloid were present and their biochemical nature was elucidated by immunohistochemistry or western blot. The risk of incorrect interpretation with misdiagnosis of systemic amyloidosis is underlined. The consequences this may have on insulin treatment are insufficiently studied.