Localised cutaneous amyloidosis at an insulin injection site

Abstract

This is a case report of a localised amyloidosis at a site of insulin injection in a 66-year-old man, clinically mimicking lipohyper-trophy. The patient has been insulin dependent diabetic since 1963, and was initially treated with bovine insulin followed by porcine insulin until switching to recombinant in the 1990s. Whilst on bovine and porcine insulin treatment, he had noticed three lumps at his regular injection sites over his right and left thigh. These sites had not been used for insulin injection since the 1990s but the lumps gradually enlarged. The microscopic examination showed masses predominantly composed of eosinophilic and partly yellow-brown, non-birefringent amorphous material that is associated with a foreign body reaction, occasional calcification, fibrosis and chronic inflammation. This stained positively with Congo red stain and displayed green birefringence of the eosinophilic material by polarised microscopy, consistent with amyloid. It is known that full-length insulin molecules are found in fibrillar form at the site of frequent insulin injections. These insulin fibrils formed in vivo display the defining characteristics of amyloid aggregates. This amyloid deposition interferes with insulin absorption, leading to suboptimal glucose control. This phenomenon is seen with both porcine and humanised insulin.