Repeated insulin injection without site rotation affects skin thickness – ultrasonographic and histological evaluation

AIMS/INTRODUCTION: The influence of repeated insulin injection on subcutaneous tissue is known, but its impact on the skin is unclear. Therefore, this study aimed to elucidate the impact of repeated insulin injections on the skin. MATERIAL AND METHODS: The properties of the skin and the subcutaneous tissue were evaluated in 52 insulin‐treated adult patients with diabetes with abnormal findings at the site of self‐injection (36 with subcutaneous nodules, 16 with suspected subcutaneous tissue induration) by ultrasonography. In all subjects, both normal and abnormal areas were examined. In addition, skin biopsies were performed in four subjects. RESULTS: The skin thickness of the normal and abnormal skin sites was 1.95 (1.60, 2.50) and 2.80 (2.27, 3.30) mm, respectively (median (first quartile, third quartile)), (P < 0.001). The biopsy specimens revealed slightly thickened and tight bundles of collagen in the dermis. Three patients had amyloid deposits in the subcutaneous tissue, and one also showed these in the dermis. These were positively stained for insulin antibody. CONCLUSIONS: Repeated insulin injection procedures result in skin thickening. Increased collagen fibers and possibly amyloid deposition in the dermis may be involved. The results reaffirmed the importance of appropriate site rotation in insulin injection and revealed the usefulness of ultrasonographic skin examination in evaluating the self‐injection procedure.