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Neuroradiology Case of the Week

Case 420

June 2009

M. F. Boomsma, MD, and A. S. A. van der Linden, MD
Sint Antonius Hospital Nieuwegein, The Netherlands

Clinical Presentation: A 22-year-old male presented with a headache that started 10 days before, along with visual impairment of the right eye. He had a VOD of 0.7 with right-sided isolated papilledema Subsequently MR imaging of the orbits and brain was performed.

Imaging Findings: See below.

Diagnosis: Optic neuritis

Discussion: The classic triad of optic neuritis (ON) consists of loss of vision, eye pain, and dyschromatopsia. Seventy percent of cases in adults are unilateral. The typical clinical course is that of eye pain and worsening visual function, which progresses over days to weeks. The eye pain usually resolves over days, often as the visual loss begins. The patients usually recover spontaneously, with recovery of visual loss beginning within 2-3 weeks and stabilizing over months. Optic neuritis not uncommonly recurs, either in the same or the contralateral eye in 28% and 35% of patients developed recurrence within 5 and 10 years, respectively. Recurrence is more common in patients who were subsequently diagnosed with multiple sclerosis (MS). Irreversible optic nerve damage occurs in up to 85% patients; however, this damage often is subclinical. As many as 80% of patients regain at least 20/30 vision, 45% within the first 4 months and 35% within 1 year. In 20% of patients long-term severe vision loss will persist. This morbidity is separate from that associated with MS.
     Whites of northern European descent are affected 8 times more frequently than blacks and Asians. Whites of Mediterranean ancestry are at intermediate risk. African blacks and Asians are rarely affected. In the United States, the male-to-female ratio for optic neuritis is 1:1.8. The mean age of onset is approximately 30 years, with most patients presenting from age 20-40 years. Autoimmune induced demyelinisation is presumed to be multifactorial in which both genetic and environmental factors predispose patients. The presence of alleles for HLA-Dw2 or HLA-DR2 is a known risk factor in the development of multiple sclerosis and optic neuritis. Viral or bacterial infection, stress, and systemic antigens and metabolites have been proposed as possible initiating events that result in autoreactive antibodies and T cells crossing the blood brain barrier and injuring myelin.
     The diagnosis of optic neuritis is usually made on clinical grounds, supplemented by ophthalmological examination findings. MRI is used to further characterize and to exclude other disease processes and to investigate the whole brain, which is the real contribution of MR imaging in the setting of ON. This is due to the fact that the most valuable predictor for the development of subsequent multiple sclerosis is the presence of white matter abnormalities. Twenty-seven to 70% of patients with isolated optic neuritis show abnormal MRI findings of the brain, as defined by 2 or more white matter lesions on T2-weighted images. In the Optic Nerve Treatment Trial, the 5-year risk of developing multiple sclerosis was 16% in patients with normal brain MRI findings, 37% with 1-2 lesions, and 51% with 3 or more lesions. At 10 years, the only statistically significant difference was between no lesions (22% risk) and one or more lesions (56% risk) [1].
     The nerve can be divided into 5 segments, anterior (45%), abutting the optic disc; mid intraorbital (61%); intracanalicular (34%); intracranial prechiasmatic (5%); and chiasmatic segments (2%). Lesions occasionally involve more than one site. The optic nerve shows mild enlargement on T1WI, focal hyperintensity on T2WI, hyperintensity on STIR and T1CE shows in more than 90% enhancement, with central enhancement being typical with a variant ‘tram track’ pattern that may simulate nerve sheath meningioma. FLAIR shows suspicious white matter foci in the brain. MR spectroscopy shows lowered choline and elevated NAA concentrations. Functional-MR shows extraoccipital activation during visual stimulation and suggests functional reorganization in response to neural impairment. The differential diagnosis of ON consists of: anterior ischemic neuropathy, infectious neuropathy, idiopathic perineuritis (pseudotumor), granulomatous optic neuropathy, optic nerve glioma, radiation induced neuropathy, drug induced neuropathy, gluten sensitivity, hypereosinophilic syndrome and vasculitis. Neuromyelitis optica, also known as Devic disease, is a rare demyelinating process that also affects the optic nerve. This disease is frequently misdiagnosed as multiple sclerosis, but it is a separate entity that is distinguished from multiple sclerosis by its severity, by disease location (affects the optic nerves and the spinal cord, sparing the brain), and by cerebrospinal fluid analysis (polymorphonuclear pleocytosis and absence of oligoclonal banding) [2].
     MRI has a direct influence on treatment, because when 2 or more WM lesions are present on MRI; treatment can decrease development of clinical definite (CD) MS and reduce the burden and number of active lesions in the future [3].
     Microscopic features in the acute setting show macrophages, lymphocytes and plasma cells together with myelin loss, axonal damage and cholesterol droplets. Oligodendocytes precursors and remyelinisation attempts suggest potential for intervention. In the chronic setting atrophy is found together with gliosis, astrocytic scar formation, axonal loss, little remyelinisation and in some cases cavitation.
     In our patient subsequent liquor investigation showed oligoclonal IgG bands, without serum oligoclonal IgG bands. A new MRI of the brain performed 3 months after onset of symptoms showed diminishing of the left temporal WM lesion without enhancement. Enhancement of the optic nerve was no longer present, but high signal intensity of the optic nerve persisted on STIR.
     At this moment findings are considered to be part of a clinical isolated syndrome (CIS), according to the revised MacDonald criteria. Prognostically this patient has a 37% chance on image findings alone, but together with the liquor findings his prognosis of developing MS worsens [4]. A new MR brain will be performed one year after onset of symptoms for further analysis.

References:

1. Kang PS, Munter FM, Swallow C. Optic neuritits. eMedicine, February 8, 2006. http://emedicine.medscape.com/article/383642-overview.
2. Harnsberger HR, Hudgins PA, Wiggins RW III, et al. Diagnostic Imaging: Head and Neck. Amirsys, 2004.
3. Polman CH, Reingold SC, Edan G, et al. Diagnostic criteria for multiple sclerosis: 2005 revisions to the "McDonald Criteria". Ann Neurol. 2005 Dec;58(6):840-6. [PubMed]
4. Tintoré M, Rovira A, Río J, et al. Baseline MRI predicts future attacks and disability in clinically isolated syndromes. Neurology. 2006 Sep 26;67(6):968-72. [PubMed]