Clinical features and outcomes of hyperglycemic hyperosmolar syndrome: a retrospective study at a Japanese university hospital.

Background: Hyperglycemic hyperosmolar syndrome (HHS) is a severe complication of diabetes, and is triggered by infection, use of corticosteroids, non-adherence to medications, and acute diseases. Despite advances in diabetes management, the clinical features and outcomes of patients with HHS remain unclear. This study aimed to investigate the clinical characteristics and prognoses of patients with HHS at a university hospital in Japan. Methods: This retrospective cohort study analyzed 84 consecutive patients diagnosed with HHS between 2018 and 2023. Patients with HHS were classified into "isolated HHS" and "mixed diabetic ketoacidosis (DKA)/HHS" groups based on established criteria. A subgroup analysis further divided the isolated HHS group into those with and without metabolic acidosis. Clinical data were collected from electronic medical records. Results: The median age of patients with HHS was 75 years, with infections (51.2%) being the most common trigger. Approximately 70% of patients did not receive diabetes medication. The isolated HHS group had a significantly higher 30-day mortality rate (26.0%) than the mixed DKA/HHS group (0%). In the isolated HHS group, those with metabolic acidosis showed markedly worse outcomes, with a 30-day mortality rate of 54.6% versus 20.7% in those without acidosis. Conclusion: HHS predominantly affects elderly patients and is often associated with poor diabetes management. The isolated HHS group had a worse prognosis than the mixed DKA/HHS group, and the presence of metabolic acidosis other than ketoacidosis significantly increased mortality. Regular blood glucose monitoring and appropriate diabetes medications are crucial for preventing the development of HHS.