Abstract
Objective: Patients with visual snow syndrome (VSS) suffer from continuous (“TV snow-like”) visual disturbance of unknown pathoetiology. In VSS, changes in cortical excitability in the primary visual cortex and the visual association cortex are discussed, with recent imaging studies tending to point to higher-order visual areas. Migraine, especially migraine with aura, is a common comorbidity. In chronic migraine and episodic migraine with aura but not in episodic migraine without aura, a reduced magnetic suppression of perceptual accuracy (MSPA) reflects a probably reduced inhibition of the primary visual cortex. Here we investigated the inhibition of the primary visual cortex using MSPA in patients with VSS, comparing that with MSPA in controls matched for episodic migraine.Methods: Seventeen patients with VSS were compared to 17 age- and migraine-matched controls. Visual accuracy was assessed by letter recognition and modulated by transcranial magnetic stimulation delivered to the occipital cortex at different intervals with respect to the letter presentation (40, 100, and 190 ms).Results: Suppression of visual accuracy at the 100-ms interval was present without significant differences between VSS patients and age- and migraine-matched controls (percentage of correctly recognized trigrams, control: 46.4 ± 34.3; VSS: 52.5 ± 25.4, p = 0.56).Conclusions: In contrast to migraine with aura, occipital cortex inhibition, as assessed with MSPA, may not be affected in VSS.
Highlights
Patients with visual snow (VS) describe continuous, mostly black and white tiny flickering dots in their entire visual field, comparable to the old TV-static noise when missing the analog signal
Its pathophysiology is still under discussion, and it is highly associated with migraine with and without aura and may partially overlap with these, recent research strongly suggests that VS is a distinct disorder [2,3,4,5]
The magnetic suppression of perceptual accuracy (MSPA) profiles of patients with visual snow syndrome (VSS) and migraine-matched controls can be seen in Figure 1 and Table 1
Summary
Patients with visual snow (VS) describe continuous, mostly black and white tiny flickering dots in their entire visual field, comparable to the old TV-static noise when missing the analog signal. Fluorodeoxyglucose-positron emission tomography (PET) investigations showed hypermetabolism in the lingual gyrus, an area of the higher visual association cortex [3, 6]. These findings from functional neuroimaging were confirmed by voxel-based morphometry by two independent groups which demonstrated increased gray matter volume in the same cortical area [6, 7]. The picture is likely more complex with studies pointing to a dysfunction of the primary visual cortex, considering thalamocortical dysrhythmia as the origin of VSS [8, 9] and demonstrating alterations in non-visual, acoustic, and limbic areas [6]
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