This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Following test is most useful in diagnosing 
Select and explain. 
A. Brainstem involvement in stroke, B. A clinically occult lesion in multiple sclerosis, C. Large hemispheral strokes, D. Spinal cord compression
B: A clinically occult lesion in multiple sclerosis
Answer: B: A clinically occult lesion in multiple sclerosis 
Explanation: 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.