Puledda F, Schankin C, Goadsby PJ. Visual snow syndrome: A clinical and phenotypical description of 1,100 cases. Neurology. 2020 Feb 11;94(6):e564-e574. doi: 10.1212/WNL.0000000000008909.
To validate the current criteria of visual snow and to describe its common phenotype using a substantial clinical database.
We performed a web-based survey of patients with self-assessed visual snow (n = 1,104), with either the complete visual snow syndrome (n = 1,061) or visual snow without the syndrome (n = 43). We also describe a population of patients (n = 70) with possible hallucinogen persisting perception disorder who presented clinically with visual snow syndrome.
The visual snow population had an average age of 29 years and had no sex prevalence. The disorder usually started in early life, and ≈40% of patients had symptoms for as long as they could remember. The most commonly experienced static was black and white. Floaters, afterimages, and photophobia were the most reported additional visual symptoms. A latent class analysis showed that visual snow does not present with specific clinical endophenotypes. Severity can be classified by the amount of visual symptoms experienced. Migraine and tinnitus had a very high prevalence and were independently associated with a more severe presentation of the syndrome.
Clinical characteristics of visual snow did not differ from the previous cohort in the literature, supporting validity of the current criteria. Visual snow likely represents a clinical continuum, with different degrees of severity. On the severe end of the spectrum, it is more likely to present with its common comorbid conditions, migraine and tinnitus. Visual snow does not depend on the effect of psychotropic substances on the brain.
Costello FE, Bisdorff AR, Robbins MS. Visual snow: Are we beginning to see the light? Neurology. 2020 Feb 11;94(6):241-242. doi: 10.1212/WNL.0000000000008913. (no abstract)
Kondziella D, Olsen MH, Dreier JP. Prevalence of visual snow syndrome in the UK. Eur J Neurol. 2020 Jan 30. doi: 10.1111/ene.14150. [Epub ahead of print]
Visual snow syndrome is a recently described condition of unknown prevalence. We investigated the prevalence in a representative population sample from the UK and tested the hypothesis that visual snow syndrome is associated with young age, headache, tinnitus and mood impairment.
Using a crowdsourcing platform, we recruited a representative sample of 1015 adult laypeople from the UK, matched for age, gender and ethnicity according to national census data. Participants were unprimed, i.e. were inquired about the "frequency of certain medical conditions" but not "visual snow syndrome".
Thirty-eight of 1015 participants reported symptoms compatible with visual snow (3.7%, 95% CI 2.7-5.2), and 22/1015 met criteria for visual snow syndrome (2.2%, 95% CI 1.4-3.3). Female-to-male ratio for visual snow syndrome was 1.6:1. Subjects with visual snow syndrome were older (50.6 ±14 years) than the population mean (44.8 ±15 years), albeit not statistically different (p=0.06). Of 22 participants with visual snow syndrome, 16 had mood symptoms (72.7%; p=0.01), 13 had headache (54.5%, p=0.06), including 5 with visual migraine aura (22.7%, p=0.15), and 13 had tinnitus (59.1%, p<0.001). No participant had diabetes or a cleft lip (control questions). Following a multivariable regression analysis to adjust for age and gender, only the association between visual snow syndrome and tinnitus remained significant (OR 3.93, 95% CI 1.63-9.9; p=0.003).
The UK prevalence of visual snow syndrome is around 2%. We confirmed an association with tinnitus, but unprimed laypeople with visual snow syndrome are on average older than those seeking medical attention.