A rare lentiform fork sign in a patient with methanol intoxication with neurological sequelae of parkinsonism and cognitive dysfunction: A case report and literature review

Methanol intoxication is rare in developed countries. Early identification and elimination of the methanol metabolites are vital to an optimal prognosis. A characteristic brain imaging finding is bilateral basal ganglia necrosis and subcortical white matter changes. Here, we report a rare neuroradiological feature called the lentiform fork sign in a patient with methanol intoxication who survived the acute poisoning stage. We report a 31-year-old woman who presented to the emergency department with acute-onset incoherent speech, consciousness disturbance, and a high-anion-gap metabolic acidosis caused by methanol intoxication. She was treated with antidote administration of fomepizole and enhanced methanol elimination through hemodialysis. Neurological sequelae of cognitive decline and parkinsonism developed, with preserved vision. Brain MRI showed bilateral putaminal necrosis and subcortical white matter changes. The apparent diffusion coefficient map showed low signal intensities in the putamen and globus pallidus bilaterally, with brightly hyperintense rims surrounding both putamina that resembled a fork, indicating a lentiform fork sign. She then had sequelae of cognitive decline and delayed parkinsonism feature, which are compatible with the brain lesions on neuroimage studies. Methanol poisoning is an uncommon life-threatening event, and neurological sequelae result from the accumulation of formic acid, a methanol metabolite that inhibits cytochrome c oxidase in mitochondria, leading to neuronal injury. Methanol intoxication should be considered in patients with imaging findings of bilateral basal ganglia necrosis with lentiform fork sign and a metabolic acidosis of unknown origin.