Diabetes complications. Artwork showing complications that can arise if a person's type 2 diabetes mellitus is not managed properly. Type 2 diabetes is caused by the pancreas not making enough insulin, cells not responding to insulin properly, or a combination of the two. Complications can include eye, kidney and nerve damage. It can also cause vascular damage that leads to ulcers, especially at the extremities. If untreated ulcers can become gangrenous and lead to amputation.