Abstract

Amyloidosis consists of a wide range of disorders characterized by the abnormal extracellular deposition of non-branching linear fibrils in numerous organs. It is classified based on the type of precursor protein that forms the amyloid fibrils and the presence of systemic or localized deposition. Repeated insulin injections at the same site have been reported to induce secondary localized insulin-derived amyloidosis (LIDA). LIDA is a rare condition that can lead to poor glycemic control and increased insulin requirement. Herein, we present an interesting case of LIDA in a 66-year-old male type 1 diabetic patient who initially sought treatment for "infected cysts" on both his thighs at previous insulin injection sites. The presumed "cysts" were drained at an urgent care and the patient was prescribed antibiotics. At the dermatology clinic, firm nodules measuring 2 to 4 cm were observed. A complete excision of the right thigh nodule was performed. Microscopic examination confirmed significant amyloid deposition in the subcutis, with vascular and interstitial involvement, supported by Congo red staining. Subsequent liquid chromatography tandem mass spectrometry analysis detected a peptide profile consistent with Ains (insulin)-type amyloid. These findings supported the diagnosis of LIDA. Left thigh nodule excision was subsequently performed, also showing amyloid deposition. In summary, LIDA is an iatrogenic form of amyloidosis confined to areas of insulin injections, without systemic involvement.  The awareness of the clinical presentation and histopathologic features of this entity is crucial in achieving an accurate diagnosis.