Metformin-Associated Encephalopathy as a Rare but Serious Adverse Effect: A Case Report

Metformin is widely prescribed as a first-line therapy for type 2 diabetes. Metformin-associated encephalopathy is a rare but serious adverse effect that can occur when the drug is inappropriately prescribed to patients with impaired renal function. Here we present the case of a 44-year-old woman undergoing maintenance hemodialysis for diabetic nephropathy who presented to the emergency department with dysarthria and generalized weakness. Although no paralysis was observed, she had difficulty maintaining posture and exhibited gait disturbance. Laboratory tests revealed metabolic acidosis (pH 7.197, bicarbonate 11.7 mmol/L) and hyperlactatemia (12.4 mmol/L). Brain magnetic resonance imaging (MRI) revealed hyperintensity in the bilateral basal ganglia. The patient had been taking metformin. Metformin was discontinued, and emergent hemodialysis was initiated, followed by continued maintenance hemodialysis; the patient's dysarthria, weakness, and abnormal findings on brain MRI subsequently rapidly improved, which confirmed the diagnosis of metformin-associated encephalopathy. Inappropriate prescription of metformin can lead to metformin-associated encephalopathy, a rare but serious adverse effect. Emergency physicians must carefully review of patients' medications and become familiar with the clinical and imaging features of metformin-associated encephalopathy.