Visual Snow: a Potential Cortical Hyperexcitability Syndrome

Abstract

The purpose of this review is to provide an overview of visual snow (VS) and provide information regarding current treatment options for VS. Visual snow (VS) is a rare disorder manifesting with a persistent visual phenomenon of seeing numerous tiny snow-like dots throughout the visual field, and it can cause debilitating visual and psychological consequences. It is emerging as a disorder separate from, but associated with, migraine visual aura, and neuronal cortical hyperexcitability is being considered as a theoretical mechanism for the persistent-positive visual symptoms. There are few studies that have investigated the treatment of VS, but as our understanding of this entity begins to change, we expect that new treatment approaches and treatment trials will emerge in the next decade. Currently, our approach is to consider pharmacologic treatment for all patients with VS who report decreased quality of life as a result of VS. Resolution of the disorder is difficult to accomplish with treatment, but in our experience, even when symptom intensity is simply reduced, many patients find that there is an improvement in their quality of life that is beneficial. Our preferred treatment options include: (1) oral lamotrigine with a slow increase from 25 mg daily to a maintenance dose of 200-300 mg daily in divided doses as tolerated, and this is typically achieved by advancing the dose in increments of 25-50 mg weekly following the first 2 weeks of therapy; (2) oral acetazolamide with an initial dose of 250 mg daily followed by a slow increase over 1-2 weeks to a total of 1000 mg daily in divided doses, and higher doses can be tolerated by some without increasing the risk-benefit ratio; or (3) oral verapamil long-acting at 120-240 mg daily, and if side effects limit the dose the can be initiated, then lower doses with short-acting verapamil two or three times daily can be substituted until higher doses with the long-acting formula can be tolerated. By initiating drug treatments with low doses and slowly increasing over 1 to 4 weeks, tolerability and compliance improves and allows patients to realize the full benefits of treatment. The proposed mechanisms of microstructural cortical abnormalities and hyperexcitability as a cause of VS may lead to new treatment approaches in the future. Until such a time, medications reported to relieve persistent visual phenomena of migraine and visual aura of migraine are treatment options worth considering and these are reviewed for that purpose. Although clinical trials for the treatment of visual snow are lacking due to the rarity of the disorder, medications reviewed here should be considered for use in patients with VS who experience an impact on their quality of life. Theoretical mechanisms that lead to cortical hyperexcitability are being investigated and could lead to new treatment options. In the meantime, medications may provide benefits in this disabling condition.

Neuro-ophthalmologic Findings in Visual Snow Syndrome

“…In particular, the anticonvulsant lamotrigine, the diuretic acetazolamide, and the calcium-channel blocker verapamil are recommended as first-line therapies for visual snow. 7 Lamotrigine down-regulates glutamate, which is known to propagate cortical spreading depression in migraine. 31 van Dongen et al 11 prescribed lamotrigine to 26 of 58 patients with visual snow syndrome, which led to partial remission in 5/26 (19.2%).…”

“…6 Beside neurological diseases, retinal diseases, persistent migraine aura, and hallucinogenic drugs must be excluded as possible causes of visual snow and palinopsia-visual snow syndrome must be diagnosed by exclusion after a thorough ophthalmic examination. 7 There are a few case series that have described ophthalmological findings of visual snow. However, none of these previous reports have included pupillary light reflex and contrast sensitivity in these patients, whereas both of these measurements are reported to be abnormal in patients with migraine visual aura.…”

“… 6 Beside neurological diseases, retinal diseases, persistent migraine aura, and hallucinogenic drugs must be excluded as possible causes of visual snow and palinopsia—visual snow syndrome must be diagnosed by exclusion after a thorough ophthalmic examination. 7 …”

Prevalence of visual snow syndrome in the UK

“…Nevertheless, a large number of publications about visual snow and visual snow syndrome have occurred in PubMed within the last 5 years (e.g. [5,6,[8][9][10][11][12][13][14]). This and extensive media coverage, as well as responses on social platforms (e.g.…”

Identification of White Matter Networks Engaged in Object (Face) Recognition Showing Differential Responses to Modulated Stimulus Strength

“…It is reasonable to suppose that primary sensory areas will show a graded response to the effective magnitude of a stimulus, whereas other regions engaged in perception may exhibit a nonlinear (even binary) response. One unexpected finding is that the magnitudes of LnL responses exhibit an opposite trend with increasing noise, which could be a feature of the responses of lingual gyrus which, for example, is also associated with visual snow syndrome, a condition in which people see white or black dots in parts or the whole of their visual fields ( Bou Ghannam and Pelak 2017 ). A fluorodeoxyglucose PET study has demonstrated hypermetabolism in the lingual gyrus in patients with visual snow syndrome ( Schankin et al.…”