Optic neuritis in demyelinating disorders

Relevance Optic neuritis (ON) can be an initial symptom of demyelinating diseases of the central nervous system (CNS). ON is divided into typical and atypical [1]. Typical ON (idiopathic or associated with MS) is characterized by unilateral damage to the optic nerve (ON), mild edema of the optic disc (ON), and rapid recovery of vision within 1 month. Atypical ON is more often associated with ONM and MOGAS. It manifests itself as bilateral damage to the ON and involvement of more than half of its length, chiasm, or optic tracts. Vision can be reduced to the point of loss of light perception, and recovery is often incomplete even with treatment with glucocorticoids [1, 3]. Atypical course of ON allows to suspect ROS or MOGAZ, especially in the presence of serological markers, such as antibodies to aquaporin-4 (AQP4-IgG) and myelin oligodendrocyte glycoprotein (MOG-IgG) [2]. ROS is a severe autoimmune disease, ON is one of the most common initial manifestations in 37–93% of patients. MOGAZ is a separate nosological form, in which ON is observed in 54–59% of patients and often has a relapsing course [3, 4]. Diagnostics of ON includes the use of optical coherence tomography (OCT), which allows to assess the thickness of the retinal nerve fiber layer (RNFL) and ganglion cell complex (GC). OCT is especially useful for assessing structural changes 6 months after ON [1]. In addition, patients with MOGAZ often have more pronounced involvement of the optic nerve along its entire length, which distinguishes them from patients with MS and MDON [5]. Objective To define the characteristic clinical manifestations of optic neuritis and to evaluate the diagnostic value of optical coherence tomography in demyelinating diseases of the central nervous system. Material and methods The study included 43 patients with demyelinating ON and 20 healthy participants. The study used OCT to assess the thickness of the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) 6 months after ON in all patients and the control group. Results Optic neuritis was the initial symptom of the disease in 75% of patients with MDON, 62% with MOGAZ, and 85.7% with MS/IDON. In the MOGAZ and MDON groups, bilateral ON was predominant. Exacerbations of ON occurred in 65% of patients with MOGAZ, in other groups they were not noted. In the AQP4-ON group, VA in the acute period was significantly lower compared to all examined groups. Complete restoration of VA was noted in patients with MS/IDON in the remote period of ON. The smallest RNFL thickness was found in the AQP4-ON group and in the MOG-ON group. Similar structural differences were found in relation to the thickness of the GCC complex. When studying the correlation of VA with OCT parameters, a direct dependence of changes in VA and RNFL thickness (K = 0.59; p < 0.001), GCC complex (K = 0.58; p < 0.001) in the remote period was found in the groups of patients with AQP4-ON and MOG-ON. Conclusion Most patients had ON symptoms at the onset of demyelinating CNS disease. The most severe course with pronounced structural damage to the optic nerve (ON) and an unfavorable prognosis for visual acuity (VA) recovery was observed with AQP4-ON. MOG-ON was characterized by a high frequency of exacerbations, which significantly affected VA in the long term and the degree of loss of the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCS). OCT can serve as an additional tool for the differential diagnosis of demyelinating forms of optic neuritis. Keywords: optic neuritis; multiple sclerosis; optical coherence tomography