Differential Diagnosis for HHS (Hyperosmolar Hyperglycemic State)

Single Most Likely Diagnosis

• Diabetic Ketoacidosis (DKA): Although HHS is a distinct entity, DKA and HHS can present similarly, with the key difference being the presence of significant ketosis in DKA. However, the clinical presentation of severe hyperglycemia and dehydration can overlap, making DKA a crucial consideration.

Other Likely Diagnoses

• Severe Dehydration: This can be due to various causes such as gastroenteritis, heat stroke, or any condition leading to significant fluid loss. Severe dehydration can present with altered mental status and hyperosmolarity, similar to HHS.
• Sepsis: Especially in elderly patients, sepsis can cause altered mental status, dehydration, and hyperglycemia, mimicking HHS.
• Stroke or Intracranial Hemorrhage: These conditions can cause altered mental status, which is a key feature of HHS. Hyperglycemia is also common in acute stroke.

Do Not Miss Diagnoses

• Meningitis or Encephalitis: Although less common, these infections can present with altered mental status and fever, and it's crucial to consider them due to their high mortality if untreated.
• Acute Coronary Syndrome: Hyperglycemia and dehydration can occur in the context of an acute coronary event, especially in diabetic patients.
• Pulmonary Embolism: This condition can cause sudden onset of symptoms, including altered mental status in severe cases, and is critical not to miss due to its high mortality.

Rare Diagnoses

• Hyperthyroid Crisis: This condition can cause hyperglycemia, dehydration, and altered mental status, although it is much less common than other diagnoses on this list.
• Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of severe hypertension, hyperglycemia, and altered mental status.
• Adrenal Insufficiency: Especially in patients with known adrenal disease, this can cause hypotension, dehydration, and altered mental status, which might be confused with HHS.