Magnetic resonance imaging (MRI), neurobehavioral testing, and toxic encephalopathy: two cases.

The objective of this investigation was to examine cerebral magnetic resonance imaging (MRI) pathology and functional deficits demonstrated by neuropsychological testing in cases of toxic encephalopathy. Two subjects, occupationally exposed to toxic chemicals, were studied. As part of their neurological assessment, MRI was done and each underwent a neuropsychological battery for patients with toxic exposures (White et al. Clin. Neuropharmacol. 13(5), 392-412, 1990). In Case 1, who was exposed to inorganic mercury, MRI showed mild central and cortical atrophy. Punctiform foci (T2) were noted in both frontal regions underlying the precentral gyri and in the subcortical myelin. Neuropsychological testing showed problems in cognitive flexibility, cognitive tracking, inhibiting perseveration, fine manual motor coordination, visuospatial analysis and organization, memory, and affect and personality. In Case 2, who was exposed to 2.6-dimethyl-4-heptanone, MRI showed multiple small foci in the white matter and pons. Neuropsychological testing indicated affective changes, deficits in manual motor speed, verbal fluency, visuospatial organization, and short-term memory. Lack of aphasia in patients with toxic encephalopathy indicates that neurotoxins probably affect subcortical and mesial temporal structures more than cortical gray matter. These MRI studies show subcortical sites of pathology.