<prompt> Following test is most useful in diagnosingBrainstem involvement in strokeA clinically occult lesion in multiple sclerosisLarge hemispheral strokesSpinal cord compression  <response>: The testing of evoked potentials is of the greatest utility in detecting subclinical spinal cord and optic nerve lesions. Up to two-thirds of persons with multiple sclerosis have neurologic deficits that are evident on visual or personal somatic evoked potentials but not on physical examination. A second lesion of this type frequently establishes the diagnosis of multiple sclerosis. Evoked potentials may be abnormal in the other conditions listed in the question. 