PHILADELPHIA – Magnetic resonance imaging of the optic nerve may help differentiate the causes of a first optic neuritis event, a study at Johns Hopkins University showed.
Optic neuritis can be a presenting symptom of both neuromyelitis optica and multiple sclerosis, Maureen Mealy, M.S.C.N., said at the annual meeting of the American Academy of Neurology. Serum antibodies can differentiate the two disorders as root causes. But early in the neuromyelitis optica (NMO) disease process, less than 20% of patients are positive for NMO immunoglobulin.
Maureen Mealy, R.N.
"It would be helpful if we could know whether the first incidence of optic neuritis was the presenting symptom of MS or NMO," said Ms. Mealy, clinical manager of the Johns Hopkins Transverse Myelitis Center and Neuromyelitis Optica Clinic, Baltimore.
To investigate the usefulness of MRI as a possible diagnostic tool, Ms. Mealy and her colleagues reviewed the records of 52 patients who presented with optic neuritis. Of these, 26 were later found to have NMO and 26 to have MS. The incident was a first event in 35% of the NMO patients and 61% of the MS patients.
Those with MS were a median of 32 years old, while those with NMO were a median of 36 years. At the time of the MRI, a test for NMO IgG was positive in 54% of those with NMO. None of the MS patients were positive for the antibody. Ms. Mealy noted that positive antibodies were more common among this NMO group than what is normally found in published studies, probably because the patients were seen at a major regional referral center.
The MRI was performed within 30 days of symptom onset. Investigators looked at some very specific regions of the optic nerve, Ms. Mealy said: the retrobulbar, canalicular, and prechiasmal segments; the chiasm; and the optic tract extending into the brain. Neuroradiologists measured the length of each lesion, and also scored each lesion by the number of involved segments. "There were a total of nine segments examined in each image – two retrobulbar, two canalicular, two prechiasmal, the chiasm, and the two optic tracts," she said.
Lesions were significantly longer among patients with NMO than among those with MS (30.5 vs. 13.5 mm). In addition, NMO-related events were significantly more likely to have multisegment lesions. Most MS-related events (19) had only one segment involved, whereas just 6 NMO events had only one segment involved. Eleven NMO events had three segments involved, two had four segments, and four had five or more segments. "There were no MS events with three or more involved segments," said Ms. Mealy, a multiple sclerosis certified nurse.
NMO-associated lesions were also more likely to be bilateral (25% vs. 0% MS lesions), and to involve the optic chiasm (25% vs. 7%) and optic tracts (18% vs. 4%).
MS lesions were more likely to be localized anteriorly in the retrobulbar and/or canalicular optic nerve (70% vs. 36% in NMO). "In contrast, 64% of NMO lesions involved the posterior pathways," she noted. "It seems that a long or extensive lesion that occurs more posteriorly could be an early biomarker for NMO."
She cautioned that the neuroradiologists were not blinded when reading the MRIs. This adds to the necessity for prospective blinded studies before imaging can be used as a predictor or diagnostic tool, she said.
Ms. Mealy said she had no financial disclosures.
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