Teaching NeuroImages: The lentiform fork sign: An MRI pattern of metformin-associated encephalopathy.

A 63-year-old woman with type 2 diabetes mellitus on hemodialysis presented with subacute onset of slurred speech and difficulty walking after 1 week of inadvertent metformin use. On examination, she had a wide-based gait, symmetric upper limb rigidity, bradykinesia, and slurred speech. Brain MRI revealed a pattern of vasogenic edema with T2/fluid-attenuated inversion recovery hyperintensity in the basal ganglia compatible with the lentiform fork sign (figure). Basal ganglia pathology has been described on the setting of metabolic acidosis and metformin use in hemodialysis patients, resulting in a parkinsonian syndrome.