Differential Diagnosis for Hyperglycemia and Ketosis

The patient's presentation of ++ ketones in urine, thirst, and a fasting glucose of 18 mmol/l suggests a state of hyperglycemia with ketosis. Here's a differential diagnosis organized into the requested categories:

• Single Most Likely Diagnosis

  • Diabetic Ketoacidosis (DKA): This condition is characterized by hyperglycemia, metabolic acidosis, and ketosis, often presenting with symptoms like thirst, polyuria, and in severe cases, altered mental status. The presence of ketones in the urine and a significantly elevated fasting glucose level strongly supports this diagnosis.

• Other Likely Diagnoses

  • Hyperglycemic Hyperosmolar State (HHS): Although HHS typically presents with less pronounced ketosis compared to DKA, it's still a consideration, especially in patients with type 2 diabetes. The key distinguishing feature would be the absence of significant ketosis and a higher glucose level.
  • Starvation Ketosis: Prolonged fasting can lead to a state of ketosis due to the body's shift towards fat metabolism for energy. However, the glucose level would typically not be as high as 18 mmol/l unless there was an underlying issue with glucose regulation.

• Do Not Miss Diagnoses

  • Pancreatitis: Especially if the patient has abdominal pain, pancreatitis could be a cause of hyperglycemia and ketosis, particularly if there's an underlying pancreatic pathology.
  • Infection: Severe infections can precipitate DKA or HHS in diabetic patients. It's crucial to evaluate for any signs of infection.
  • Medication-induced Hyperglycemia: Certain medications, such as steroids and some psychiatric medications, can cause hyperglycemia. Identifying and managing these potential causes is critical.

• Rare Diagnoses

  • Cushing's Syndrome: This endocrine disorder can cause hyperglycemia due to excess cortisol production. However, it would be an uncommon initial presentation.
  • Pheochromocytoma: Although rare, this tumor of the adrenal gland can cause episodes of hyperglycemia among other symptoms like hypertension and tachycardia.
  • Glucagonoma: A rare tumor of the pancreas that produces excess glucagon, leading to hyperglycemia. It's characterized by a distinct rash (necrolytic migratory erythema), weight loss, and diabetes.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory results, and medical history to determine the most appropriate course of action.