Almost all diabetic patients experience swings in blood glucose levels, which are larger and less predictable than in nondiabetics. When these swings become intolerable and cause disruption to the person's daily life and/or prolonged hospitalization, the person is labeled as having "labile" or "brittle" diabetes. Although brittle diabetes is uncommon (less than 1 percent of insulin-taking diabetic patients) , it can cause a considerable burden on hospital, social, and family resources due to multiple hospital admissions.
The clinical manifestations, diagnosis, and management of brittle diabetes will be reviewed here. General principles of insulin therapy in diabetes mellitus are reviewed elsewhere. (See "General principles of insulin therapy in diabetes mellitus" and "Management of blood glucose in adults with type 1 diabetes mellitus" and "Insulin therapy in type 2 diabetes mellitus".)
Most experts would define brittle diabetes as severe instability of blood glucose levels with frequent and unpredictable episodes of hypoglycemia and/or ketoacidosis that disrupt quality of life. The unpredictable episodes of hypoglycemia and/or ketoacidosis are due to an absolute insulin dependency (undetectable C-peptide levels). Thus, brittle diabetic patients virtually always have type 1 diabetes.
The majority of the published clinical literature regarding brittle diabetes is old with few modern-day descriptions of brittle diabetes encompassing the era of intensive insulin therapy [2,3]. With the availability of basal and bolus insulin regimens, using long and rapid-acting insulin analogs or insulin pump therapy, there has been substantial improvement in the ability to treat most patients with type 1 diabetes effectively . Although most clinical experts in the management of type 1 diabetes continue to see patients with brittle diabetes mellitus, many of whom have a substantial behavioral or iatrogenic contribution to their brittle state, the modern day course of such patients has not been well described.
Three clinical presentations of brittle diabetes have been described: (1) predominant hyperglycemia with recurrent ketoacidosis, (2) predominant hypoglycemia, and (3) mixed hyper- and hypoglycemia . Frequent hypoglycemia, even if asymptomatic, causes both defective glucose counterregulation and hypoglycemia unawareness and thus a vicious cycle of recurrent hypoglycemia. (See "Physiologic response to hypoglycemia in normal subjects and patients with diabetes mellitus", section on 'Hypoglycemia-associated autonomic failure'.)