RESULTS
The study was conducted with 130 eyes of 65 patients, 44 (67.7%) male and 21 (32.3%) female, whose ages ranged from 18 to 59. The mean age was 39.68 ± 9.99 years. The cases were divided into two groups as ”MS Group” (n = 70) and ”Control Group” (n = 60). The duration of the disease in the MS group ranges between 2 and 25 years, with a mean of 14.74 ± 5.85 years and a median of 15 years. According to MS types; twenty-nine (44.6%) of the cases had RRMS and six (9.2%) had SPMS type. There was no statistically significant difference between the groups in terms of ONSD, SWE ON, SWE OD, and SWE perineural area levels (p> 0.05). (Table 1).
In the MS group; there is no statistically significant difference between patients with and without optic neuritis, in terms of mean age, gender distribution, MS duration, MS types, ONSD, SWE ON, SWE OD, SWE perineural area, and EDSS levels (p> 0.05). (Table 2). There is no statistically significant difference in terms of ONSD, SWE ON, SWE OD, and SWE perineural area between the MS patients with optic neuritis and the control group (p> 0.05). (Table 3). There is no statistically significant difference in terms of ONSD, SWE ON, SWE OD, and SWE perineural area between the MS patients without optic neuritis and the control group (p> 0.05). (Table 4)
DISCUSSION : MS is an autoimmune, chronic, inflammatory, and demyelinating disease. While MS can lead to optical neuritis, internuclear ophthalmoplegia, nystagmus, and saccadic dysmetria as visual dysfunction, optic neuritis is the most frequently detected one.15 It is often associated with severe visual loss. Therefore, early diagnosis of optic nerve damage is extremely important. Recently, ultrasonography has become an important adjuvant in the evaluation of the optic nerve.16 We performed this study considering that SWE can be an effective modality for evaluating the optic nerve in the early diagnosis of optic neuritis due to non-invasive and low-cost properties.
Volume loss and axonal damage in the retinal nerve fibers can be observed in MS patients.15 The optic disc usually appears normal but is mildly edematous in one-third of cases.17 Also, autoimmune-related posterior uveitis or vasculitis of the optic nerve in Wegener’s granulomatosis may cause optic disc edema.18 This effect of autoimmune pathologies on the optic disc may cause damage by similar mechanisms in MS patients. The presence of the vascular network in the perineural area may play a role in the development of optical neuritis by having immune cells in this autoimmune inflammatory process.19 Thus, we thought that the evaluation of the perineural area might be beneficial and added this area to our research. In the literature, these parameters have been evaluated with MRI in different studies.20-22 However, there is no study in which all three parameters were evaluated together on SWE.
In the literature, there is only one study evaluating sonoelastographic findings in patients with MS, and only the optic nerve was evaluated in this study.13 Besides, in another study; Batur et al. evaluated both ON and retrobulbar tissue in patients with isolated optic neuritis on SWE and reported that comparison of the normal eye with isolated optic neuritis. The stiffness of the optic nerve in optic neuritis was found higher than the contralateral normal optic nerve and this difference was statistically significant.23 In our study, we aimed to develop a different point of view; the optic disc and perineural area were also evaluated in addition to the optic nerve, and quantitative evaluation was made particularly on SWE to increase the reliability of the study. Our study has been the first to evaluate all these parameters together. Besides, we strengthened the clinical effectiveness of our study by comparing our SWE measurements with the EDSS score. EDDS is widely used in clinical trials and for the assessment of MS. Since we thought the EDDS and sonoelastographic parameters might have a relation, we also compared the SWE results with the EDDS scores. Unfortunately, we could not find any significant differences.
In Inal et al.’s study, the sonoelastographic changes in the optic nerve in patients with MS were evaluated in terms of the elasticity of the optic nerve based on the three main colorings in strain elastography (SE) and SWE.13 According to this study, both SE and SWE can be used to investigate inflammation in patients with MS and may provide early diagnosis of optic neuritis. In our study, no statistically significant difference was found in the comparison of the optic nerve, optic disc, and perineural area SWE measurements between the MS patients (with or without optic neuritis attack) and healthy volunteers. According to these findings, our study results do not support the results which they reported.
At this point, the disadvantages of SWE arise such as the difficulty of the measurement technique and dependence on the operator. Optic nerve diameter up to 5 mm is considered normal in a healthy population.24,25 Inal et al. found that the mean optic nerve diameter was 5.31 ± 0.48 mm (range, 3.8–6.5) in MS patients, while this value was 5.22 ± 0.58 mm (range, 3.7–7) in healthy volunteers. These findings support the concerns about the measurement. In our study, this value was 3.03 ± 0.58 mm in the healthy population and it was compatible with the information in the literature.
Optic neuritis may cause increased or decreased ONSD in the acute and chronic phases.16,26,27 This may be an early and late sign of optic neuritis. The hypothesis that optic nerve thickness and stiffness may differ in optic neuritis with MS patients is the study’s main purpose. However, we could not find any significant difference in ONSD and SWE ON between patient groups with and without control and optic neuritis. According to the optic neuritis stage, we anticipate that non-classified patients may have led to these results.
One of the limitations of our study is that SWE is an operator-dependent measurement method. Although our small size of the patient population seems to be a problem, the prospective study design increases the reliability of our results.