Abnormal Connectivity and Brain Structure in Patients With Visual Snow

Abstract

Objective: Visual snow (VS) is a distressing, life-impacting condition with persistent visual phenomena. VS patients show cerebral hypermetabolism within the visual cortex, resulting in altered neuronal excitability. We hypothesized to see disease-dependent alterations in functional connectivity and gray matter volume (GMV) in regions associated with visual perception.

Methods: Nineteen patients with VS and 16 sex- and age-matched controls were recruited. Functional magnetic resonance imaging (fMRI) was applied to examine resting-state functional connectivity (rsFC). Volume changes were assessed by means of voxel-based morphometry (VBM). Finally, we assessed associations between MRI indices and clinical parameters.

Results: Patients with VS showed hyperconnectivity between extrastriate visual and inferior temporal brain regions and also between prefrontal and parietal (angular cortex) brain regions (p < 0.05, corrected for age and migraine occurrence). In addition, patients showed increased GMV in the right lingual gyrus (p < 0.05 corrected). Symptom duration positively correlated with GMV in both lingual gyri (p < 0.01 corrected).

Conclusion: This study found VS to be associated with both functional and structural changes in the early and higher visual cortex, as well as the temporal cortex. These brain regions are involved in visual processing, memory, spatial attention, and cognitive control. We conclude that VS is not just confined to the visual system and that both functional and structural changes arise in VS patients, be it as an epiphenomenon or a direct contributor to the pathomechanism of VS. These in vivo neuroimaging biomarkers may hold potential as objective outcome measures of this so far purely subjective condition.

Keywords: functional connectivity; lingual gyrus; temporal cortex; visual snow; visual system.

FIGURE 1

Illustration of resting-state functional connectivity (rsFC) differences comparing healthy controls (HCs) to patients with visual snow (VS). (A) Patients with VS showed significantly increased rsFC (connections labeled in blue) compared to that in HCs. Results are shown at p < 0.05 (all t-values > 3.3), false discovery rate (FDR) seed level corrected (with additional correction for age and migraine occurrence). X, Y, and Z denote Montreal Neurological Institute (MNI) coordinates. (B) Effect sizes for both groups for significant rsFC between-group differences (^∗p-values). These plots are shown for illustrative purposes only to demonstrate that the observed effects are mainly due to higher positive correlations in patients than in controls (i.e., they are not the result of weaker anticorrelations between regions). Abbreviations: atFUS, anterior temporal fusiform gyrus; pTFUS, posterior temporal fusiform gyrus; IOTG, inferior occipito-temporal gyrus; AG, angular gyrus; IFG, inferior frontal gyrus; aITG, anterior inferior frontal gyrus; IFG, inferior frontal gyrus; MidFG, middle frontal gyrus; FEF, frontal eye field; pSTG, posterior superior temporal gyrus; LPFC, lateral prefrontal cortex; L, left; R, right.

FIGURE 2

Overlay of structural differences (shown in sagittal, coronal, and axial slices) between healthy controls (HCs) and patients with visual snow (VS). Increases in gray matter volume were seen in the right (R) lingual gyrus [p = 0.014, family-wise error (FWE) corrected, t-value = 4.61] in the patient group when compared to controls.

FIGURE 3

Association between gray matter volume and disease duration. A positive correlation was seen in the bilateral lingual gyrus [p < 0.05, family-wise error (FWE) corrected].