Hyperglycemia after stroke also occurs frequently in nondiabetic patients. One meta-analysis reported that hyperglycemia during the acute stroke period increased inhospital or 30-day mortality by about threefold [9]. In this analysis, it is difficult to conclude that hyperglycemia produced an independent negative effect because more severe stroke is associated with higher glucose levels. Therefore, there has been a long debate about whether hyperglycemia should be controlled in nondiabetic patients. There has been only one clinical trial to address this question, the GIST-UK trial [10]. In this study, patients with hyperglycemia after stroke (diabetic 17%, nondiabetic 83%) received a glucose-potassium-insulin infusion (n = 464) in the treatment group, while the control group received a saline infusion (n = 469). Outcomes of this study were 90-day death and severe disability. Unfortunately, the study was terminated early because of delayed recruitment and limitations of financial resources. In this underpowered study, blood glucose control with insulin infusion had no effect on the outcomes. There have been no other studies examining this issue, so the effect of blood glucose control in acute stroke cannot be concluded. However, insulin therapy did not show any tendency of improvement in nondiabetic stroke patients in this study, and we do not need to make any fuss about it. In our opinion, if blood glucose is episodically over 200 mg/dL in nondiabetic patients, it is better to observe it without treatment. Blood glucose control should be considered if the level is consistently above 200 mg/dL and should be maintained at 140–180 mg/dL according to the current guideline recommendation. The possibility of unrecognized diabetes should be investigated using HbA1c.

Most clinical practice guidelines or textbooks on stroke rarely get into the specifics of diabetes management. They usually refer readers to the current guidelines from diabetes organizations such as the American Diabetes Association. In fact, there is no reason for long-term management of diabetes to be different in the presence or absence of stroke. Based on the principles of diabetes management, it may not be so difficult even to stroke physicians. However, the actual situation during the acute stage of stroke is not so comfortable for them, because of the complicated categories of diabetes medications and the new drugs that become available each year, and diabetes physicians often intervene in consultation. The situation may vary greatly from one country to another, but such consultations often exacerbate a simple problem. Unfamiliar with stroke situations, they may easily provide an insulin prescription during the acute stage, although the use of non-insulin antidiabetic agents is preferable, and the insulin therapy might persist for a long time without being noticed by the stroke physicians. Insulin therapy should be restricted to special situations or to patients with advanced diabetes, because of the risk of frequent hypoglycemia and low compliance due to its invasiveness. In this case, diabetes control may become worse, and the possibility of recurrence of the vascular event may increase. Even with a diabetes consultant, stroke physicians must understand the basics of diabetes care and the concept of antidiabetic drug use. This is because diabetes management is a long and distant voyage from the beginning to prevent the patient from driving the wrong way.

Before going into the details on diabetes care, just remember one principle. Stroke causes stress hyperglycemia. If needed, insulin therapy should be used temporarily to control this but should be discontinued when the patient is stable. In the same way, when the dosage of non-insulin antidiabetic agent is increased during the acute stage, it should be reduced during the chronic stage. Glucose monitoring should be performed frequently at least during the 3 months after stroke along with appropriate adjustment of antidiabetic medications. The following is a summary of the core content of long-term diabetes management. We have tried to describe the approach of antidiabetic medications from mild to severe diabetes to make it as easy as possible, even if you are unfamiliar with diabetes care.