Unmasking Diabetic Ketoacidosis in a Patient with Metformin Associated Lactic Acidosis

Lactic Acidosis is a very rare, dangerous side effect associated with metformin use. The incidence of Metformin-associated Lactic Acidosis (MALA) ranges between 3.3 to 4.7/100,000 patient-years. It carries a mortality rate of around 30%. We present a unique case of severe lactic acidosis in a type 2 diabetic patient presenting as MALA with diabetic ketoacidosis.

Case Description:

A 48-year female with hypertension and type-2 diabetes mellitus on metformin was brought to the emergency department for a 1-week history of progressively worsening nausea with intractable vomiting, generalized weakness, and altered sensorium. A review of her records showed that she had been diagnosed with renal insufficiency 2 years ago (effective glomerular filtration rate of 11 and serum creatinine of 4.0) for which she failed to follow-up and had continued to take metformin at 2 g/day. Arterial blood gas on presentation showed a pH of 6.602, pCO2 of 20 mmHg, pO2 of 67 mmHg, and a bicarbonate of < 6 mEq/L, with an anion gap greater than 24. Her blood glucose was 333mg/dL with a raised beta-hydroxybutyrate (BHB) of 4.68mmol/L and HbA1c of 9.4. Despite starting a bicarbonate drip immediately, the patient developed a cardiac arrest. Hypothermia protocol for cardiac arrest was followed, and immediate hemodialysis was performed. Post-dialysis, the pH improved to 7.509, and the patient became hemodynamically stable. However, her anion gap remained high at 20 with a worsening BHB level at 10.11 mmol/L. After starting a fixed-dose insulin drip (0.1U/kg/hr), the high anion gap metabolic acidosis resolved and BHB reduced to 0.26 mmol/L.

Discussion:

Initially treated as MALA, the patient had significant clinical improvement following hemodialysis. Although the serum pH returned to normal, the high anion gap metabolic acidosis and elevated BHB resolved only following insulin administration. MALA and diabetic ketoacidosis, though pathologically different conditions, can present similarly making it difficult to differentiate. It is essential to consider and treat multiple etiologies of metabolic acidosis whenever present.