Diseases and Disorders

Visual Snow Syndrome: An Overview

Shadt Skawratananond


Introduction

Visual snow syndrome is a neurological disorder characterized by a constant visual disturbance of tiny, flickering dots that can be likened to the static of an untuned television. Visual snow has been very recently introduced into medical literature, so little research has been conducted [1]. The exact causes of visual snow are also unknown. There are other symptoms that accompany the disorder, such as photophobia (sensitivity to light), palinopsia (afterimages), nyctalopia (difficulty seeing at night), and entoptic phenomena (seeing images from within the eye itself), migraines, and tinnitus [2]. Researchers have proposed a theoretical mechanism for the disorder through a controlled analysis of patients with positron emission tomography: hypermetabolism of the supplementary visual cortex (lingual gyrus) [3]. The current population of those affected by visual snow syndrome is unknown. Despite this, have modern research techniques advanced enough to determine the treatment and pathology of visual snow syndrome?
 

Unknown Cause and Spectrum Quality of Visual Snow Syndrome

Neurologically, the cause of visual snow syndrome was an anomaly until neuroimaging studies found higher metabolism levels in the lingual gyrus. A study found that patients with visual snow syndrome had brighter colors in the lingual gyrus than shown in the healthy control group through the use of [(18) F]-2-fluoro-2-deoxy-D-glucose positron emission tomography and statistical parametric mapping (statistical significance was defined by P < 0.001). Another way that researchers had observed visual snow syndrome was through visual evoked potential (VEP) tests, which feature measurements of the electrical activities in the brain observed directly in response to visual stimuli. Researchers paired the VEP test with a “double-pulse” test (two visual stimuli presented in quick succession) and found that the VEP revealed gamma-band neural oscillations (a peculiar indication) in the patients of visual snow syndrome. What was concluded from this test was that patients of visual snow syndrome had diminished inhibitory activity in the visual cortex, and therefore an unusual VEP potentiation [5]. 

Visual snow syndrome also varies in severity; not all patients were shown to possess all the symptoms that accompanied the disorder. The least severe patients were shown to have only visual snow and no other symptoms, while the most severe patients had visual snow in addition to every existing symptom in the disorder, including tinnitus and migraine aura. There are some notable statistical observations about the disorder: the most prevalent static present in the syndrome was black and white, the most prevalent visual symptoms were floaters, afterimages, and photophobia, and the most prevalent non-visual symptoms were migraine aura and tinnitus [5]. 

 

Relationship With Other Diseases

Visual snow syndrome and comorbid migraine auras have been observed to be linked. One study that had 120 patients with visual snow observed that 70 of those patients had typical migraines and 37 had migraines with auras. To clarify, auras are visual phenomena that fall under one of the following conditions: blind spots (scotomas), floating zigzag lines across the visual field, shimmering spots or stars, flashes of light, and vision loss [3]. Comorbid migraines, the study found, aggravates the following symptoms of visual snow syndrome in patients: palinopsia (afterimages), nyctalopia (difficulty seeing under dim light conditions), and entoptic phenomena (visual effects occurring within the eye itself, such as floaters and vascular figures). However, it must be noted that visual snow syndrome and migraine auras are completely distinct disorders. Visual snow syndrome has a clear biological basis, in which there is hypermetabolism in the lingual gyrus, while migraine auras are associated with cortical hyperexcitability in areas surrounding the lingual gyrus which accompany photophobia, a prevalent symptom of migraine aura.

In addition to this, visual snow and tinnitus have also been observed to be linked in a similar fashion. In a study, roughly 63% of the visual snow patients also reported continuous bilateral tinnitus, suggesting an underlying, common pathophysiological basis [4]. However, no studies have yet found a definitive cause of the relationship between tinnitus and visual snow syndrome.

Hallucinogen persisting perception disorder (HPPD) has also been linked to visual snow syndrome. HPPD is characterized by a series of visual symptoms that follow the usage of a hallucinogenic drug, which shares many of the same symptoms as visual snow syndrome, such as visual static and palinopsia. HPPD also causes other symptoms, such as flashes and intensified colors. The distinguishing factor between HPPD and visual snow syndrome is that HPPD is acquired post-usage of a recreational drug, while visual snow is present at birth. Thus, visual snow syndrome is independent of the use of recreational drugs, while HPPD can be manifested in the visual snow spectrum [8].

 

Treatments and Current Research

Currently, there is no cure for visual snow syndrome. However, there are treatments available that diminish the severity of the disorder and help ease patients’ quality of life. A cocktail of three oral drugs has been shown to be effective in reducing, but not ending, migraine aura and tinnitus: lamotrigine, acetazolamide, and verapamil. This cocktail is given in low doses and is gradually increased for 4 weeks. Other treatments have included a cocktail of lamotrigine, valproate, topiramate, acetazolamide, and flunarizine, which was found to be slightly effective. Nevertheless,  lamotrigine was found to be the most effective individual prescription to treat the symptoms of migraine auras in visual snow syndrome [6]. 

 

Conclusion

The scope of visual snow syndrome is largely unknown. The disorder was introduced in 1995, but fewer than 10 cases existed before 2014. In the last four years, however, the number of cases has grown to approximately 200 [7]. Large scale research studies for visual snow syndrome have been limited due to its rarity. This rarity can be attributed to the fact that many of those with the low-severity form of visual snow syndrome live their lives without knowing that their visual fields are abnormal. Although, with a wider breadth of communication and awareness of symptoms, perhaps the number of reported cases of visual snow syndrome will increase enough so that research will be conducted to provide those with more severe visual snow syndrome a better quality of life. 


References


  1. Puledda F, Schankin C, Digre K, Goadsby PJ. (01/02/2018). Visual snow syndrome: what we know so far. PubMed. https://pubmed.ncbi.nlm.nih.gov/29140814/. Retrieved: 16/08/2020.

  2. Genetic and Rare Diseases Information Center.  (13/08/2020). “Visual Snow Syndrome.” Genetic and Rare Diseases Information Center, U.S. Department of Health and Human Services. rarediseases.info.nih.gov/diseases/12062/visual-snow-syndrome. Retrieved: 16/08/2020.

  3. Schankin CJ, Goadsby PJ. (29/05/2015). Visual snow--persistent positive visual phenomenon distinct from migraine aura. Springer Link. https://link.springer.com/article/10.1007/s11916-015-0497-9. Retrieved: 17/08/2020.

  4. Renze M. (01/06/2017). Visual Snow Syndrome and Its Relationship to Tinnitus. PubMed. https://pubmed.ncbi.nlm.nih.gov/28723606/. Retrieved: 17/08/2020.

  5. Puledda F, Schankin C, Goadsby PJ (11/02/2020). Visual snow syndrome: A clinical and phenotypical description of 1,100 cases. PubMed. https://pubmed.ncbi.nlm.nih.gov/31941797/. Retrieved: 17/08/2020.

  6. Bou Ghannam A, Pelak VS. 13/03/2013). Visual Snow: a Potential Cortical Hyperexcitability Syndrome. PubMed. https://pubmed.ncbi.nlm.nih.gov/28349350/. Retrieved: 17/08/2020.

  7. Metzler AI, Robertson CE. (22/06/2018). Visual Snow Syndrome: Proposed Criteria, Clinical Implications, and Pathophysiology. PubMed. https://pubmed.ncbi.nlm.nih.gov/29934719/. Retrieved: 17/08/2020.

  8. Puledda, Francesca, et al. (11/02/2020). “Visual Snow Syndrome.” Neurology. https://n.neurology.org/content/94/6/e564. Retrieved: 18/08/2020.

  9. Schankin, Christoph J, et al. (24/03/2020). “Structural and Functional Footprint of Visual Snow Syndrome.” OUP Academic, Oxford University Press. https://academic.oup.com/brain/article/143/4/1106/5811372. Retrieved: 18/08/2020.

  10. Puledda, Francesca, et al. (10/03/2020). “Insular and Occipital Changes in Visual Snow Syndrome: a BOLD FMRI and MRS Study.” Wiley Online Library. https://onlinelibrary.wiley.com/doi/full/10.1002/acn3.50986. Retrieved: 18/08/2020.

Shadt Skawratananond

Shadt Skawratananond


Student at Westwood High School. Competed at the 2019 USA National Brain Bee.