Differential Diagnosis

The patient presents with symptoms of not eating and drinking, elevated blood glucose (6.2), ketones (1.6), tachycardia, nausea, and a history of anorexia nervosa. Here's a differential diagnosis organized into categories:

• Single Most Likely Diagnosis
  • Diabetic Ketoacidosis (DKA): Although the blood glucose is not extremely high, the presence of ketones, tachycardia, and nausea, especially in the context of not eating or drinking (which can lead to dehydration and exacerbate DKA), makes DKA a strong consideration. The patient's history of anorexia nervosa could complicate the clinical picture, potentially masking typical symptoms of DKA.
• Other Likely Diagnoses
  • Dehydration: Not eating and drinking can lead to dehydration, which is compounded by tachycardia and nausea. Dehydration can also contribute to or exacerbate other conditions.
  • Starvation Ketoacidosis: Given the patient's history of anorexia nervosa and the presence of ketones, starvation ketoacidosis is a possibility. This condition occurs when the body starts breaking down fat for energy due to lack of food intake.
  • Gastroenteritis: Nausea and not eating or drinking could suggest a gastrointestinal infection, which could lead to dehydration and potentially affect blood glucose and ketone levels.
• Do Not Miss Diagnoses
  • Septic Shock: Although less likely, septic shock can present with tachycardia, nausea, and altered mental status. It's crucial to consider and rule out infection, especially in a patient who may be immunocompromised due to malnutrition from anorexia nervosa.
  • Cardiac Conditions (e.g., Myocarditis, Cardiomyopathy): Tachycardia could be a sign of underlying cardiac issues, which might be precipitated or worsened by the patient's nutritional status and dehydration.
• Rare Diagnoses
  • Thyroid Storm: This is a life-threatening condition that requires immediate attention. Although rare, it could present with tachycardia, nausea, and altered mental status, among other symptoms.
  • Adrenal Insufficiency: Given the patient's history of anorexia nervosa, which can affect the endocrine system, adrenal insufficiency is a rare but possible diagnosis that could present with nausea, tachycardia, and changes in blood glucose levels.

What to Do

1. Immediate Assessment and Stabilization: Ensure the patient's airway, breathing, and circulation (ABCs) are stable. Provide oxygen if necessary and start IV fluids for hydration.
2. Laboratory Tests: Conduct a complete blood count (CBC), basic metabolic panel (BMP), blood glucose, ketone levels, and consider thyroid function tests and cortisol levels given the patient's history.
3. Monitor Vital Signs: Closely monitor the patient's vital signs, including heart rate, blood pressure, temperature, and respiratory rate.
4. Nutritional Support: Consider consulting a nutritionist to provide appropriate nutritional support, taking into account the patient's history of anorexia nervosa.
5. Psychiatric Evaluation: Given the patient's history of anorexia nervosa, a psychiatric evaluation may be necessary to address any underlying issues contributing to the current condition.
6. Consider Transfer to a Higher Level of Care: If the patient's condition worsens or if there are concerns about the ability to manage the patient's complex medical and psychiatric needs in the current setting, consider transfer to a hospital with more resources.