Insights into pathophysiology and treatment of visual snow syndrome: A systematic review.

BACKGROUND: Visual snow syndrome is a debilitating disorder characterized by tiny flickering dots (like TV static) in the entire visual field and a set of accompanying visual (palinopsia, enhanced entoptic phenomena, photophobia, nyctalopia), nonvisual (e.g. tinnitus) and nonperceptional (e.g. concentration problems, irritability) symptoms. Its pathophysiology is enigmatic and therapy is often frustrating.

OBJECTIVES: To summarize our current understanding of pathophysiology and treatment of visual snow syndrome.

METHODS: A systematic search of PubMed database was performed using the key word "visual snow" and predefined in- and exclusion criteria. The results were stratified into "treatment" and "pathophysiology." Additionally, we conducted a search with the key words "persistent migraine aura" and "persistent visual aura" and screened for mis-diagnosed patients actually fulfilling the criteria for visual snow syndrome. The reference lists of most publications and any other relevant articles known to the authors were also reviewed and added if applicable.

RESULTS: From the 50 original papers found by searching for "visual snow," 21 were included according to the inclusion and exclusion criteria. Additional four publications came searching for "persistent migraine aura" or "persistent visual aura." Further publications derived from literature references resulting in a total of 20 articles for pathophysiology and 15 for treatment with some overlaps. Regarding pathophysiology, hyperexcitability of the visual cortex and a processing problem of higher order visual function are assumed, but the location is still in discussion. In particular, it is unclear if the primary visual cortex, the visual association cortex or the thalamocortical pathway is involved. Regarding treatment, data is available on a total of 153 VSS patients with medication mentioned for 54 resulting in a total of 136 trials. From the 44 different medications tried, only eight were effective at least once. The best data is available for lamotrigine being effective in 8/36 (22.2%, including one total response and no worsening), followed by topiramate being effective in 2/13 (15.4%, no total response and one worsening). The only other medication resulting in worsening of VSS was amitriptyline according to our literature review. The others reported to be effective at least once were valproate, propranolol, verapamil, baclofen, naproxen and sertraline. The nonpharmacological approach using color filters of the yellow-blue color spectrum might also be helpful in some patients.

CONCLUSIONS: Visual snow syndrome is still far from being fully understood. In respect of pathophysiology, a disorder of visual processing is likely. The best pharmacological evidence exists for lamotrigine, which can be discussed off-label. As nonpharmacological option, patients might benefit from tinted glasses for everyday use.