B

Diplopia that appears when the patient looks to the left and the right eye fails to adduct is the classic pattern of a right internuclear ophthalmoplegia, produced by a lesion of the right medial longitudinal fasciculus; this fits the examination finding far better than meningitis, a generalized “cranial neuritis,” or merely stating the underlying cause (demyelination) [Obuchowska & Mariak, 2009, PMID 19673451].