The old classifications of diabetes are breaking down.
Type 1 used to be called juvenile onset diabetes, but is suffered by many later in life. It is more properly classified as an autoimmune disease in which the islet cells of the pancreas are attacked by the immune system.
Type 2 diabetes is the end result of the metabolic syndrome in which insulin resistance plays the central role. High abdominal obesity promotes resistance to the action of insulin and poor glucose management. This is part of a more complex cascade, but the end stage is extreme resistance to the action of insulin and eventual pancreatic insulin insufficiency. The pancreas may eventually collapse and cease to produce insulin in the “burn out” stage.
Type 1.5 diabetes is a way to describe the progression from type 1 diabetes to the conditions of type 2 diabetes. Poor insulin and glucose management lead to high insulin resistance in the type 1 diabetic. Thus, the apparent paradox that someone whose pancreas fails to produce insulin may become resistant to the action of insulin. Likely, this individual has become obese in the abdominal region from injecting too much insulin to control blood glucose. The fat produces hormones that make one insulin resistant. The progression is thus from insulin insufficiency to excess insulin (exogenously produced and injected) to insulin receptor burn out.