LD is one of the most common complications of subcutaneous insulin injections and may present as either lipohypertrophy (LH) or lipoatrophy (LA). LA is defined as a large, often profound, retracted scar on the skin that results from serious damage to subcutaneous fatty tissue, probably of an immunological etiology.
LH represents the majority of LD cases with the areas of thickened subcutaneous fat tissue confined to frequently used insulin injection sites in the form of painless induration, swelling, and nodules lacking an external sign. In etiology, two main local factors are considered: tissue trauma caused by poor injection habits, such as insufficient injection site rotation, frequent needle reuse, and insulin molecule strong growth-promoting power.