Iatrogenic, insulin-dependent, local amyloidosis.

Human and experimental amyloidosis can occur either as a generalized widespread deposit of various proteins or a localized deposit. We looked for local amyloidosis caused iatrogenically under clinical and experimental conditions. Subcutaneous tissue from one diabetic patient and six Wistar rats, which had received a continuous local infusion of 1.2 iu of insulin daily for 6 weeks, was examined histologically. In all cases the development of granulation tissue around the tip of the catheter was observed. In addition, inhomogenous extracellular deposits showing green birefringence under polarized light when stained Congo red were seen. Immunohistologically, they displayed binding of anti-insulin antibody. Electron microscopy demonstrated a typical spear-like fibrillar structure with a fibril diameter of 60 to 80 A. These findings confirmed that the deposited substance was amyloid. Iatrogenically administered protein produced in vivo amyloidosis at the site of its entry. Insulin can lead to the formation of amyloid fibrils not only in vitro but also in vivo.