Differential Diagnosis

The patient presents with a complex clinical picture, including metabolic acidosis (pH 7.1, HCO3 17, CO2 40), elevated creatinine (200 umol), unconsciousness, fever, new cellulitis to the groin, and a history of type 2 diabetes mellitus (T2DM) on metformin. Here's a structured approach to the differential diagnosis:

• Single Most Likely Diagnosis

  • Septic Shock with Metformin-Associated Lactic Acidosis (MALA): The combination of fever, new cellulitis (a potential source of infection), unconsciousness, and metabolic acidosis in a patient with T2DM on metformin suggests septic shock. The elevated creatinine level indicates renal impairment, which could be exacerbated by sepsis or MALA. Metformin can cause lactic acidosis, especially in the context of renal failure or severe infection.

• Other Likely Diagnoses

  • Diabetic Ketoacidosis (DKA): Although less likely given the absence of specific mention of ketones, DKA remains a possibility, especially with the patient's history of T2DM and the presence of metabolic acidosis. However, the absence of ketosis information and the presence of a clear infectious source (cellulitis) makes septic shock more likely.
  • Sepsis-induced Acute Kidney Injury (AKI): The elevated creatinine suggests AKI, which could be secondary to sepsis, hypovolemia, or nephrotoxic agents. The patient's fever and cellulitis support a septic cause.
  • Urosepsis: Given the groin cellulitis, there's a possibility of a urinary tract infection as the source of sepsis, especially if the cellulitis is related to a urinary tract infection complication.

• Do Not Miss Diagnoses

  • Meningitis or Encephalitis: Although less likely, given the absence of specific neurological signs, these conditions can present with fever, altered mental status, and can be rapidly fatal if not treated promptly.
  • Intra-abdominal Sepsis: An intra-abdominal source of infection (e.g., diverticulitis, appendicitis) could explain the sepsis and metabolic acidosis. This diagnosis is critical to consider because it may require surgical intervention.

• Rare Diagnoses

  • Ethylene Glycol or Methanol Poisoning: These can cause metabolic acidosis but are less likely given the clinical context (fever, cellulitis) that strongly suggests an infectious etiology.
  • Isolated Lactic Acidosis from Other Causes: While lactic acidosis can occur from various causes (e.g., biguanide toxicity, liver disease), the presence of an infectious source makes septic shock a more likely explanation for the patient's condition.