Subclinical Optic Neuritis in Neuromyelitis Optica

Abstract

We read with great interest the review of neuromyelitis optica (NMO) by Morrow and Wingerchuk (1). Even with proposed diagnostic criteria (2), establishing the diagnosis of NMO may be difficult. We describe a patient with white matter cerebral lesions, myelitis, and subclinical optic neuritis with negative NMO-IgG at the initial presentation. The diagnosis of NMO became certain 5 months later when the patient developed overt bilateral optic neuritis and a positive NMO-IgG antibody. A 46-year-old woman experienced the onset of dizziness, nausea, and vomiting. Neurological examination was unremarkable except for horizontal gaze evoked nystagmus and mild weakness in her right leg. Muscle strength in the right lower extremity was at 4/5, patellar deep tendon reflexes were hypoactive, and the plantar reflex was indifferent on the right side. Vision was 20/20 bilaterally with normal color vision, funduscopy, and visual evoked potentials. Automated visual fields demonstrated mild generalized depression (Fig. 1).FIG. 1: Visual fields show mild generalized loss bilaterally (mean deviation: right, −3.83 dB; left, −4.44 dB).Brain magnetic resonance imaging (MRI) revealed enhancement of the entire length of the left optic nerve (Figs. 2A and 2B) hyperintensities in the dorsal medulla, around the fourth ventricle, in the periaqueductal gray matter, mammillary bodies, the thalamus, and in the vicinity of the third ventricle (Fig. 2C). MRI of the spine showed T2 hyperintensity extending through cervical and thoracic spinal cord (Fig. 2D). Serum biochemistries, complete blood count, and erythrocyte sedimentation rate were normal, as were serological tests for herpes virus family, cytomegalovirus, Epstein-Barr virus, antinuclear antibody, anti-Smith antibody, anti-soluble substance-A and anti-soluble substance-B, anti-Jo-1, anti-Scl-70 antibody, anticardiolipin antibodies, and NMO-IgG. Cerebrospinal fluid was acellular, without oligoclonal bands, normal glucose, and increased protein of 271 mg/dL (normal, 15–45 mg/dL).FIG. 2: Contrast-enhanced T1 axial (A) and coronal (B) magnetic resonance imaging (MRI) shows enhancement of the left optic nerve (arrows). C. Axial fluid-attenuated inversion recovery image demonstrates an increased signal (arrows) surrounding the third ventricle. D. Sagittal T2 MRI of the spine shows a longitudinally extensive lesion from the medulla to the thoracic cord.The patient was treated intravenously with 1,000 mg of methylprednisolone/day for 7 days. She returned to our clinic 5 months later with pain in the right eye and blurred vision in both eyes. Visual acuity was 20/50 in the right eye, and 20/200 in the left eye. The right optic disc was swollen, and the left disc was pale. Visual evoked potentials were abnormal bilaterally, and NMO-lgG antibody was now found to be positive. Our case is instructive for 2 reasons. First, patients with NMO may present with clinical and neuroimaging findings highly suggestive of NMO, yet NMO-IgG antibody may not be detected. Given that the sensitivity of this test is 73% (3), repeat testing is warranted if clinical suspicion is high and initial results are negative. Second, patients with NMO may present with subclinical optic neuropathy. At presentation, our patient only had mild visual field changes, yet MRI revealed contrast enhancement of the left optic nerve. To our knowledge, this observation has not been reported previously.