A 35-year-old female has progressive numbness of the right arm and difficulty see­ing objects in the left visual field. She is known to be HIV positive,but has not consistently taken medications in the past. On examination,she appears healthy,but has a right homon­ymous hemianopsia and decreased sensory perception in her left upper extremity and face. Her CD4 count is 75 cells per fA,and her MRI is consistent with a demyelinating lesion of the left parietooccipital are