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Multiple Events May Trigger Visual Snow

Visual snow, a mostly spontaneous phenomenon that may be related to migraine, appears to be triggered by inciting events, systemic illness, or lesions along the visual pathway, researchers reported at the virtual annual scientific meeting of the American Headache Society.

Patients often describe visual snow as similar to seeing black and white or colorful flickering dots like 'television static,' said the lead study author Dev Mehta, DO, a fellow in neurology at the Mayo Clinic in Rochester, MN.

To learn more about possible causes, the researchers performed a retrospective chart review of patients who presented to the Mayo Clinic between January 1994 and January 2020; they looked for the search term "visual snow." They also collected demographic data including age at symptom onset, duration of follow-up, history of migraine, visual snow characteristics, comorbid diagnoses, treatments and their response, and neurologic and ophthalmologic evaluations.

Among the 248 patients who met study criteria, comorbid migraine was present in 79 percent; 33.5 percent had tinnitus, 29.4 percent, depression, and 49.6 percent, anxiety, said Dr. Mehta, who will soon be moving to do a fellowship in psychiatry at the University of Washington in Seattle.

The research team scrutinized the cases of 88 individuals who had underlying causes for visual snow phenomena or could identify an inciting event. Among those events, one person attributed visual snow to a neoplastic occurrence, three to infections, and four to intracranial hypertension. Visual snow occurred with ocular pathology in seven people, posterior cortical atrophy in one person, and hallucinogen-persistent perception disorder in 10 persons.

"We also identified 41 patients with transient visual snow, including 37 with visual snow as their migraine aura," Dr. Mehta said. "Some patients had partial improvement with lamotrigine, topiramate, acetazolamide, and benzodiazepines. No patient experienced complete remission."

Commenting on the study, Marc Dinkin, MD, director of neuro-ophthalmology and associate professor of ophthalmology and of neurology at Weill Cornell Medical College and NewYork Presbyterian Hospital, said: "As researchers such as Dr. Mehta and his colleagues describe visual snow and show the gamut of triggers, they shine a light on the possibility that there is a true inciting event, which would help us understand the mechanism and allow us to manage it."

Dr. Dinkin said he sees patients with visual snow frequently. "In some cases, visual snow may occur contemporaneously with other medical conditions. Whether all of the 88 of 248 cases in Dr. Mehta's study—where there was an inciting event—reflected true causation as opposed to association remains to be seen," Dr. Dinkin said.

"In either case, it should be recognized that what the authors were looking at was just the symptom 'visual snow' as opposed to the 'visual snow syndrome,' which tends to be accompanied by other symptoms such as after images, trailing images, photophobia, nyctalopia, entopic phenomena, photopsia, tinnitus, and migraine. 

"In some of their cases, especially those with ocular pathology, the symptom may reflect structural retinal pathology and therefore encompass a pathological process quite different from visual snow syndrome, which appears to be related to changes in regions of the cortex," he said. "I look forward to reading the study authors' full manuscript when it is published."

Disclosures: Drs. Mehta and Dinkin had no relevant disclosures.

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AHS Abstract: Mehta D, Garza I, Robertson CE. Visual snow case series: Review of 248 cases with attention to underlying causes or inciting events.