Should Most Patients With Optic Neuritis be Tested for Neuromyelitis Optica Antibodies and Should This Affect Their Treatment?

Pain Symptoms in Optic Neuritis

Signs and symptoms of optic neuritis (ON), an autoimmune disorder of the central nervous system (CNS), differ between patients. Pain, which is commonly reported by ON patients, may be the major reason for some patients to visit the clinic. This article reviews the presence of pain related to ON with respect to underlying disorders, including multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocyte glycoprotein associated disease (MOGAD). The aim of this review is to provide an overview of pain symptoms in accordance with the context of various pathophysiological explanations, assist in differential diagnosis of ON patients, especially at the onset of disease, and make recommendations to aid physicians make decisions for follow up diagnostic examinations.

Visual impairment

This chapter can guide the use of imaging in the evaluation of common visual syndromes: transient visual disturbance, including migraine and amaurosis fugax; acute optic neuropathy complicating multiple sclerosis, neuromyelitis optica spectrum disorder, Leber hereditary optic neuropathy, and Susac syndrome; papilledema and pseudotumor cerebri syndrome; cerebral disturbances of vision, including posterior cerebral arterial occlusion, posterior reversible encephalopathy, hemianopia after anterior temporal lobe resection, posterior cortical atrophy, and conversion blindness. Finally, practical efforts in visual rehabilitation by sensory substitution for blind patients can improve their lives and disclose new information about the brain.

The Correlation between Aquaporin-4 Antibody and the Visual Function of Patients with Demyelinating Optic Neuritis at Onset

ON patients with AQP4-Ab seropositivity tend to be predominantly female and young and have worse visual acuity and more severe damage to their visual fields compared with AQP4-Ab seronegativity.

Neuromyelitis optica and aquaporin-4 (AQP4) autoantibodies in consecutive optic neuritis patients in Southern Finland

PURPOSE

  To analyse the frequency of neuromyelitis optica (NMO) among consecutive optic neuritis (ON) patients in Southern Finland and the feasibility of Aquaporin-4 (AQP4) autoantibody assay in the diagnosis of NMO.

METHODS

  Consecutive patients with symptoms suggestive of acute ON and managed in the Helsinki University Central Hospital were evaluated critically screened for AQP4 autoantibody during a 47.5-month period. The antibodies were determined using radioimmunoprecipitation method. AQP4 index >15 was considered positive, 10-15 borderline and <10 normal. Brain magnetic resonance imaging (MRI) was performed for all patients.

RESULTS

  Of the 300 patients with suspected ON, 191 were eventually diagnosed as ON, and 66 (35%) of them had a previous diagnosis or were diagnosed with multiple sclerosis (MS). Of the 125 patients without MS diagnosis, 62 (50%) had demyelinative lesions in MRI, which is a risk factor for developing MS. Two patients (1.1%; 95% CI 0.3-4.5) fulfilled the criteria of NMO. Positive AQP4 antibodies were found in three patients (1.6% 95% CI 0.3-4.5), one of them had NMO, one had MS and one became diagnosed with MS a month later. Borderline autoantibody levels were found in 10 patients, 7 of whom had MS.

CONCLUSIONS

  NMO is rare among ON patients in the population of Southern Finland. In this small cohort, the sensitivity and positive predictive values of the AQP4 autoantibody index for NMO were low, 1/2 and 1/3 respectively, and do not support initiating routine screening.

Optic neuritis in neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune demyelinating disease associated with recurrent episodes of optic neuritis and transverse myelitis, often resulting in permanent blindness and/or paralysis. The discovery of autoantibodies (AQP4-IgG) that target aquaporin-4 (AQP4) has accelerated our understanding of the cellular mechanisms driving NMO pathogenesis. AQP4 is a bidirectional water channel expressed on the plasma membranes of astrocytes, retinal Müller cells, skeletal muscle, and some epithelial cells in kidney, lung and the gastrointestinal tract. AQP4 tetramers form regular supramolecular assemblies at the cell plasma membrane called orthogonal arrays of particles. The pathological features of NMO include perivascular deposition of immunoglobulin and activated complement, loss of astrocytic AQP4, inflammatory infiltration with granulocyte and macrophage accumulation, and demyelination with axon loss. Current evidence supports a causative role of AQP4-IgG in NMO, in which binding of AQP4-IgG to AQP4 orthogonal arrays on astrocytes initiates complement-dependent and antibody-dependent cell-mediated cytotoxicity and inflammation. Immunosuppression and plasma exchange are the mainstays of therapy for NMO optic neuritis. Novel therapeutics targeting specific steps in NMO pathogenesis are entering the development pipeline, including blockers of AQP4-IgG binding to AQP4 and inhibitors of granulocyte function. However, much work remains in understanding the unique susceptibility of the optic nerves in NMO, in developing animal models of NMO optic neuritis, and in improving therapies to preserve vision.