Low-contrast stimuli superior for detecting first-episode optic neuritis
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Low-contrast visual evoked potential was superior to conventional high-contrast visual evoked potential for the diagnosis of first-ever optic neuritis, according to a study published in Frontiers in Neurology.
“Optic neuritis (ON) detection is important for the early diagnosis and management of multiple sclerosis and neuromyelitis optica spectrum disorder,” Soo-Hyun Park, PhD, of the departments of neurology and critical care medicine at Inha University in South Korea, and colleagues wrote. “However, the conventional high-contrast visual evoked potential used for ON detection lacks sensitivity for identifying ON presenting as mild or unremarkable visual disturbance, which is common in first-episode ON.”
In a retrospective survey, Park and colleagues reviewed the medical records of patients with ON, multiple sclerosis (MS) or neuromyelitis optica spectrum disorder between January 2013 and December 2016. They assessed 60 patients with demyelinating diseases, including 29 with MS and 31 with idiopathic ON, and 32 healthy controls. Thirty-nine eyes had first-ever ON, and 81 eyes did not have ON (non-ON).
Researchers induced visual evoked potentials (VEP) using three pattern-reversal checkerboard stimuli: 10% contrast with a check size of 32’ (LC32), 100% contrast with a check size of 32’ (HC32, conventional VEP) and 100% contrast with a check size of 16’ (HC16). They calculated area under the curve (AUC) to determine the most fitting VEP method for identifying optic nerve involvement.
Compared with first-ever ON and healthy eyes, LC32 had the highest AUC for detecting ON (0.750, P < .001), followed by HC32 (0.730, P < .001) and HC16 (0.702, P = .001).
Further, LC32 and HC32 VEPs were abnormal in 76.9% and 43.6% in first-ever ON eyes, respectively, and in 53.1% and 9.9% of non-ON eyes, respectively. Those VEPs were abnormal in 34.4% and 6.3% of control eyes. The combination of tests did not improve sensitivity in any group, according to researchers.
“We revealed that LC32 VEP is superior to conventional HC32 VEP or HC16 VEP for detecting first-ever ON,” Park and colleagues wrote. “These findings imply that VEP with LC stimulation might be more sensitive than conventional HCVEP to detect ON without remarkable visual impairment.”
Perspective
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ON can be difficult to diagnose clinically, especially in mild cases of visual disturbance. We know from the Optic Neuritis Treatment Trial that treatment with corticosteroids speeds up visual recovery but does not influence visual outcome. Therefore, if the visual disturbance is mild, treatment may be deferred.
This study focused on improving sensitivity of VEP to detect first-episode ON, which is often mild. While low-contrast VEP (LCVEP) was more sensitive than conventional high-contrast VEP (HCVEP), half of the non-ON eyes and one-third of the controls had abnormalities.
While LCVEP shows promise in detecting mild and asymptomatic ON, there are a few limitations to the study. Eyes with acute ON or with first attack less than 6 months prior were excluded. Further studies to identify sensitivity in acute episodes and correlation of clinical examination data with abnormal LCVEP would be helpful to hopefully improve specificity.
The 2017 McDonald criteria to diagnose MS requires evidence of dissemination in time and space. If the McDonald criteria is revised to include the optic nerve as a site for dissemination in space, the ability to diagnose mild or asymptomatic ON may be more critical for earlier diagnosis of demyelinating diseases.
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