Visual snow syndrome: A clinical and phenotypical description of 1,100 cases

Puledda, Francesca; Schankin, Christoph; Goadsby, Peter J. (2020). Visual snow syndrome: A clinical and phenotypical description of 1,100 cases. Neurology, 94(6), e564-e574. American Academy of Neurology 10.1212/WNL.0000000000008909

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Objective: To validate the current criteria of visual snow and to describe its common phenotype using a substantial clinical database.

Methods: 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.

Results: 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.

Conclusions: 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.

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