This patient should have an MRI of the brain. She has symptoms and signs consistent with optic neuritis, including pain with eye movement, central scotoma, and an afferent pupillary defect. Although idiopathic optic neuritis can occur, the most common cause is multiple sclerosis (MS). An MRI of the brain should be obtained to evaluate for brain lesions consistent with MS. If they are present, a diagnosis of MS is likely on the basis of the official diagnostic criteria. These criteria require clinical and radiologic dissemination of lesions in space and time. In this patient, the occurrence of two disparate clinical events happening at separate times satisfies criteria for dissemination in time, and the presence of an optic nerve (cranial nerve II) lesion (detected on clinical examination) and additional brain lesions (if shown by MRI) would satisfy criteria for dissemination in space.
Determination of the erythrocyte sedimentation rate (ESR) has no role in the evaluation of MS. ESR elevation can occur in giant cell arteritis, a potential cause of visual loss, but this is typically a condition of older patients. In addition, this patient has not had the symptom of a headache.
Although a lumbar puncture is often performed when evaluating a patient for MS, the presence or absence of oligoclonal bands in the cerebrospinal fluid (CSF) is not part of any MS diagnostic criteria. Approximately 10% to 15% of patients with MS do not have these bands in their CSF, and their presence, by itself, is a nonspecific finding. If an MRI confirms the diagnosis of MS, CSF examination is unnecessary.
A rapid plasma reagin test is a screening test for syphilis. The classic pupillary abnormality of neurosyphilis is the Argyll-Robertson pupil, in which pupils are unreactive to light but constrict to accommodation. This patient instead manifested an afferent pupillary defect, which is a sign of reduced optic nerve (cranial nerve II) conductance. Although optic nerve inflammation can be a complication of meningovascular neurosyphilis, this scenario is quite rare, and this patient shows no other concerning signs or symptoms for this condition.